We introduce the concept of a superlinear threshold detector, a detector that has a higher probability to detect multiple photons if it receives them simultaneously rather than at separate times. Highly superlinear threshold detectors in quantum key distribution systems allow eavesdropping the full secret key without being revealed. Here, we generalize the detector control attack, and analyze how it performs against quantum key distribution systems with moderately superlinear detectors. We quantify the superlinearity in superconducting singlephoton detectors based on earlier published data, and gated avalanche photodiode detectors based on our own measurements. The analysis shows that quantum key distribution systems using detector(s) of either type can be vulnerable to eavesdropping. The avalanche photodiode detector becomes superlinear toward the end of the gate. For systems expecting substantial loss, or for systems not monitoring loss, this would allow eavesdropping using trigger pulses containing less than 120 photons per pulse. Such an attack would be virtually impossible to catch with an optical power meter at the receiver entrance.
Realtime determination of laser beam quality by modal decomposition
Oliver A. Schmidt, Christian Schulze, Daniel Flamm, Robert Bruening, Thomas Kaiser, Siegmund Schroeter, Michael Duparre
We present a realtime method to determine the beam propagation ratio M2 of laser beams. The alloptical measurement of modal amplitudes yields M2 parameters conform to the ISO standard method. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods. (C) 2011 Optical Society of America
Growth of doped silicon nanowires by pulsed laser deposition and their
analysis by electron beam induced current imaging
B. Eisenhawer, D. Zhang, R. Clavel, A. Berger, J. Michler, S. Christiansen
Doped silicon nanowires (NWs) were epitaxially grown on silicon substrates by pulsed laser deposition following a vapourliquidsolid process, in which dopants together with silicon atoms were introduced into the gas phase by laser ablation of lightly and highly doped silicon target material. pn or p(++)p junctions located at the NWsilicon substrate interfaces were thus realized. To detect these junctions and visualize them the electron beam induced current technique and twopoint probe currentvoltage measurements were used, based on nanoprobing individual silicon NWs in a scanning electron microscope. Successful silicon NW doping by pulsed laser deposition of doped target material could experimentally be demonstrated. This doping strategy compared to the commonly used doping from the gas phase during chemical vapour deposition is evaluated essentially with a view to potentially overcoming the limitations of chemical vapour deposition doping, which shows doping inhomogeneities between the top and bottom of the NW as well as between the core and shell of NWs and structural lattice defects, especially when high doping levels are envisaged. The pulsed laser deposition doping technique yields homogeneously doped NWs and the doping level can be controlled by the choice of the target material. As a further benefit, this doping procedure does not require the use of poisonous gases and may be applied to grow not only silicon NWs but also other kinds of doped semiconductor NWs, e. g. group III nitrides or arsenides.
Photonic quantum walks in a fiber based recursion loop
A. Schreiber, K. N. Cassemiro, V. Potocek, A. Gabris, I. Jex, Ch Silberhorn
We present a flexible and robust system for implementing onedimensional coined quantum walks. A recursion loop in the optical network together with a translation of the spatial into the time domain ensures the possible increment of the step number without need of additional optical elements. An intrinsic phase stability assures a high degree of coherence and hence guarantees a good scalability of the system. We performed a quantum walk over 27 steps and analyzed the 54 output modes. Furthermore, we estimated that up to 100 steps can be realized with only minor changes in the used components.
Robustness of bipartite Gaussian entanglement subject to channel losses
A. S. Villar, F. A. S. Barbosa, A. S. Coelho, A. J. de Faria, K. N. Cassemiro, P. Nussenzveig, M. Martinelli
Entanglement as a collective property of quantum systems follows its own dynamics as environmental disturbances enter the quantum channel. It can either withstand undesired external influences or completely vanish even for very small disturbances. Only the first kind of quantum states are suitable for real applications in quantum networks. We show the conditions under which a bipartite Gaussian state remains entangled under partial energy loss of one party.
Timeresolved detection and mode mismatch in a linear optics quantum
gate
Linear optics (LO) is a promising candidate for the implementation of quantum information processing protocols. In such systems, single photons are used to represent qubits. In practice, single photons from different sources will not be perfectly temporally and frequency matched. Therefore, understanding the effects of temporal and frequency mismatch is important in characterizing the dynamics of the system. In this paper, we discuss the impact of temporal and frequency mismatch, how they differ from each other and what their effect is on a simple LO quantum gate. We show that temporal and frequency mismatch have inherently different effects on the operation of the gate. We also consider the spectral effects of the photodetectors, focusing on timeresolved detection, which we show has a strong impact on the operation of such protocols.
Theory of PhotoionizationInduced Blueshift of Ultrashort Solitons in
GasFilled HollowCore Photonic Crystal Fibers
Mohammed F. Saleh, Wonkeun Chang, Philipp Hoelzer, Alexander Nazarkin, John C. Travers, Nicolas Y. Joly, Philip St. J. Russell, Fabio Biancalana
We show theoretically that the photoionization process in a hollowcore photonic crystal fiber filled with a Ramaninactive noble gas leads to a constant acceleration of solitons in the time domain with a continuous shift to higher frequencies, limited only by ionization loss. This phenomenon is opposite to the wellknown Raman selffrequency redshift of solitons in solidcore glass fibers. We also predict the existence of unconventional longrange nonlocal soliton interactions leading to spectral and temporal soliton clustering. Furthermore, if the core is filled with a Ramanactive molecular gas, spectral transformations between redshifted, blueshifted, and stabilized solitons can take place in the same fiber.
Optomechanical selfchannelling of light in freely suspended
dualplanarwaveguide structure
A. Butsch, F. Biancalana, C. Conti, P. St. J. Russell
Conference on Lasers and ElectroOptics
(2011)
It is shown that optomechanical forces can cause nonlinear selfchannelling of light in two parallel silica nanowebs suspended inside a fibre capillary. The effective optical nonlinearity is a million times higher than the Kerr effect.
Modulational instability and solitons in excitonic semiconductor
waveguides
Oleksii A. Smyrnov, Fabio Biancalana, Stefan Malzer
Nonlinear light propagation in a singlemode micronsize waveguide made of semiconducting excitonic material has been theoretically studied in terms of exciton polaritons by using an analysis based on macroscopic fields. When a light pulse is spectrally centered in the vicinity of the groundstate Wannier exciton resonance, it interacts with the medium nonlinearly. This optical cubic nonlinearity is caused by the repulsive excitonexciton interactions in the semiconductor, and at resonance it is orders of magnitude larger than the Kerr nonlinearity (e.g., in silica). We demonstrate that a very strong and unconventional modulational instability takes place, which has not been previously reported. After reducing the problem to a single nonlinear Schrodingerlike equation, we also explore the formation of solitary waves both inside and outside the polaritonic gap and find evidence of spectral broadening. A realistic physical model of the excitonic waveguide structure is proposed.
Adaptive frequency comb illumination for interferometry in the case of
nested twobeam cavities
Irina Harder, Gerd Leuchs, Klaus Mantel, Johannes Schwider
The homogeneity test of glass plates in a Fizeau interferometer is hampered by the superposition of multiple interference signals coming from the surfaces of the glass plate as well as the empty Fizeau cavity. To evaluate interferograms resulting from such nested cavities, various approaches such as the use of broadband light sources have been applied. In this paper, we propose an adaptive frequency comb interferometer to accomplish the cavity selection. An adjustable FabryPerot resonator is used to generate a variable frequency comb that can be matched to the length of the desired cavity. Owing to its flexibility, the number of measurements needed for the homogeneity test can be reduced to four. Furthermore, compared to approaches using a twobeam interferometer as a filter for the broadband light source, the visibility of the fringe system is considerably higher if a FabryPerot filter is applied. (C) 2011 Optical Society of America
Rate analysis for a hybrid quantum repeater
Nadja K. Bernardes, Ludmila Praxmeyer, Peter van Loock
We present a detailed rate analysis for a hybrid quantum repeater assuming perfect memories and using optimal probabilistic entanglement generation and deterministic swapping routines. The hybrid quantum repeater protocol is based on atomic qubitentanglement distribution through optical coherentstate communication. An exact, analytical formula for the rates of entanglement generation in quantum repeaters is derived, including a study on the impacts of entanglement purification and multiplexing strategies. More specifically, we consider scenarios with as little purification as possible and we show that for sufficiently low local losses, such purifications are still more powerful than multiplexing. In a possible experimental scenario, our hybrid system can create nearmaximally entangled (F = 0.98) pairs over a distance of 1280 km at rates of the order of 100 Hz.
Highly Efficient SinglePass Source of Pulsed SingleMode Twin Beams of
Light
Andreas Eckstein, Andreas Christ, Peter J. Mosley, Christine Silberhorn
We report the realization of a bright ultrafast type II parametric downconversion source of twin beams free of any spatiotemporal correlations in a periodically poled KTiOPO(4) (PPKTP) waveguide. From a robust, singlepass setup it emits pulsed twomode squeezed vacuum states: photonnumber entangled pairs of singlemode pulses or, in terms of continuous variables quantum optics, pulsed EinsteinPodolskyRosen states in the telecom wavelength regime. We verify the singlemode character of our source by measuring Glauber correlation functions g((2)) and demonstrate with a pump energy as low as 75 pJ per pump pulse a mean photon number of 2.5.
CatalystFree Functionalization for Versatile Modification of
Nonoxidized Silicon Structures
Here we report on a simple, catalystfree route for obtaining highly versatile subsequent functionalization on Si nanowires and Si(111) substrates. The versatility of this approach allows subsequent functionalization not only for organic species but also for inorganic (nanomaterial) species. The method has the advantage of controlling, the density of reactive crosslinkers without affecting the stability of the Si samples and without having metallic (or catalyst) residues on the surface. This method also allows formation Of monolayers with a variety of termination groups and is expected to open up a. wide range of,opportunities for producing stable molecule based (opto)electronic and (bio)sensing devices Immobilization of inorganic nanomaterial on the Si, samples offers advanced opportunities in molecular switches, (bio)sensors, molecular Scale memory, and Si based nanoelectronic devices.
Novel aspects of pulse propagation in photonic crystal fibers
We present a review of our recent research on the use of photonic crystal fibers (PCFs) to manipulate the propagation of ultrashort pulses. The combination of a high nonlinear coefficient and unusual wavelengthdependent groupvelocitydispersion "landscapes", together with the ability to taper the properties along the fiber by thermal postprocessing, allows observation of many interesting effects. These include generation of THz trains of equidistant sub50 fs pulses, highly efficient supercontinuum generation from the UV to the IR, soliton collisions and observation for the first time of a soliton blueshift, counteracting the Ramanrelated soliton selffrequency shift.
Spin Hall effect of light in metallic reflection
N. Hermosa, A. M. Nugrowati, Andrea Aiello, J. P. Woerdman
OPTICS LETTERS
36(16)
32003202
(2011)
We report the first measurement of the spin Hall effect of light (SHEL) on an airmetal interface. The SHEL is a polarizationdependent outofplane shift on the reflected beam. For the case of metallic reflection with a linearly polarized incident light, both the spatial and angular variants of the shift are observed and are maximum for 45 degrees/45 degrees polarization, but zero for pure s and p polarization. For an incoming beam with circular polarization states however, only the spatial outofplane shift is present. (C) 2011 Optical Society of America
Direct generation of a multitransverse mode nonclassical state of
light
Benoit Chalopin, Francesco Scazza, Claude Fabre, Nicolas Treps
Quantum computation and communication protocols require quantum resources which are in the continuous variable regime squeezed and/or quadrature entangled optical modes. To perform more and more complex and robust protocols, one needs sources that can produce in a controlled way highly multimode quantum states of light. One possibility is to mix different single mode quantum resources. Another is to directly use a multimode device, either in the spatial or in the frequency domain. We present here the first experimental demonstration of a device capable of producing simultanuously several squeezed transverse modes of the same frequency and which is potentially scalable. We show that this device, which is an Optical Parametric Oscillator using a selfimaging cavity, produces a multimode quantum resource made of three squeezed transverse modes. (C) 2011 Optical Society of America
Parallel twostep phaseshifting digital holograph microscopy based on a
grating pair
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA AOPTICS IMAGE SCIENCE AND
VISION
28(3)
434440
(2011)

Journal
An optical configuration for parallel twostep phaseshifting digital holographic microscopy (DHM) based on a grating pair is proposed for the purpose of realtime phase microscopy. Orthogonally circularly polarized object and reference waves are diffracted twice by a pair of gratings, and two parallel copies for each beams come into being. Combined with polarization elements, parallel twostep phaseshifting holograms are obtained. Based on the proposed configuration, two schemes of DHM, i.e., slightly offaxis and onaxis DHM, have been implemented. The slightly offaxis DHM suppresses the dc term by subtracting the two phaseshifting holograms from each other, thus the requirement on the offaxis angle and sampling power of the CCD camera is reduced greatly. The onaxis DHM has the least requirement on the resolving power of the CCD camera, while it requires that the reference wave is premeasured and its intensity is no less than 2 times the maximal intensity of the object wave. (C) 2011 Optical Society of America
Systematic analysis of signaltonoise ratio in bipartite ghost imaging
with classical and quantum light
G. Brida, M. V. Chekhova, G. A. Fornaro, M. Genovese, E. D. Lopaeva, I. Ruo Berchera
We present a complete and exhaustive theory of signaltonoiseratio in bipartite ghost imaging with classical (thermal) and quantum (twin beams) light. The theory is compared with experiment for both twin beams and thermal light in a certain regime of interest.
MultimJ carrier envelope phase stabilized fewcycle pulses generated by
a tabletop laser system
A. Anderson, F. Luecking, T. Prikoszovits, M. Hofer, Z. Cheng, C. C. Neacsu, M. Scharrer, S. Rammler, P. St J. Russell, G. Tempea, et al.
APPLIED PHYSICS BLASERS AND OPTICS
103(3)
531536
(2011)

Journal
A compact system for the generation of fewcycle multimJ Carrier Envelope Phase (CEP) stabilized pulses is presented. At the output 1.9 mJ, 5.7 fs pulses were achieved after hollow fiber compression (HFC) of 5 mJ, 25 fs circularlypolarized pulses from a Ti:sapphire multipass chirped pulse amplifier (CPA). Polarization control of the generated pulses was done using all reflective phase retarders which can be nearly arbitrarily scaled for increasing energies. The CEP noise from the amplifier system is shown to be 190 mrad rms over a period of more than 7 hours. The full system, i.e., oscillator, amplifier, CEP stabilization, and HFC is compact enough to fit on a standard optical table.
Generation of Kerr nonGaussian motional states of trapped ions
NonGaussian states represent a powerful resource for quantum information protocols in the continuous variables regime. Cat states, in particular, have been produced in the motional degree of freedom of trapped ions by controlled displacements dependent on the ionic internal state. An alternative method harnesses the Kerr nonlinearity naturally present in this kind of system. We perform detailed calculations confirming its feasibility for typical experimental conditions. Additionally, this method permits generation of all other complex nonGaussian states with negative Wigner functions resulting from Kerr nonlinear interaction. Especially, superpositions of several coherent states are achieved at a fraction of the time necessary to produce the cat state. Copyright (C) EPLA, 2011
Quantummechanical theory of optomechanical Brillouin cooling
Matthew Tomes, Florian Marquardt, Gaurav Bahl, Tal Carmon
We analyze how to exploit Brillouin scattering of light from sound for the purpose of cooling optomechanical devices and present a quantummechanical theory for Brillouin cooling. Our analysis shows that significant cooling ratios can be obtained with standard experimental parameters. A further improvement of cooling efficiency is possible by increasing the dissipation of the optical antiStokes resonance.
Quantum Effects in Optical Fibers
Gerd Leuchs, Christoph Marquardt
2011 OPTICAL FIBER COMMUNICATION CONFERENCE AND EXPOSITION (OFC/NFOEC)
AND THE NATIONAL FIBER OPTIC ENGINEERS CONFERENCE
(2011)
The quantization of the light field is important for understanding some aspects of optical fiber systems: the quantum limit of amplifiers, the dynamics of solitons below shot noise and the appearance of nonclassical light.
Demonstration of Unconditional OneWay Quantum Computations for
Continuous Variables
Ryuji Ukai, Noriaki Iwata, Yuji Shimokawa, Seiji C. Armstrong, Alberto Politi, Junichi Yoshikawa, Peter van Loock, Akira Furusawa
Oneway quantum computation is a very promising candidate to fulfill the capabilities of quantum information processing. Here we demonstrate an important set of unitary operations for continuous variables using a linear cluster state of four entangled optical modes. These operations are performed in a fully measurementcontrolled and completely unconditional fashion. We implement three different levels of squeezing operations and a Fourier transformation, all of which are accessible by selecting the correct quadrature measurement angles of the homodyne detections. Though not sufficient, these linear transformations are necessary for universal quantum computation.
Limitation on Effective Area of Bent LargeModeArea Leakage Channel
Fibers
JOURNAL OF LIGHTWAVE TECHNOLOGY
29(17)
26092615
(2011)

Journal
We investigate the bending characteristics of leakage channel fibers (LCFs) to achieve large mode area (LMA) and effectively singlemode operation with a practically allowable bending radius for compact Ybdoped fiber applications. Through numerical simulations, carried by the fullvectorial finiteelement method, we present the limitations on the effective area of LCFs under bent condition and compare their limits with that of conventional stepindex LMA fibers. Due to a better controllability of the low numerical aperture and a large value of the differential bending loss (similar to 20 dB/m) between the fundamental and higher order modes in LCFs, the LMA of similar to 500 mu m(2) (core diameter of similar to 36 mu m) at 1064 nm can be achieved when the optimized LCF is bent into a 10 cm bending radius.
Macroscopic Pure State of Light Free of Polarization Noise
Timur Sh. Iskhakov, Maria V. Chekhova, Georgy O. Rytikov, Gerd Leuchs
The preparation of completely nonpolarized light is seemingly easy; an everyday example is sunlight. The task is much more difficult if light has to be in a pure quantum state, as required by most quantumtechnology applications. The pure quantum states of light obtained so far are either polarized or, in rare cases, manifest hidden polarization; even if their intensities are invariant to polarization transformations, higherorder moments are not. We experimentally demonstrate the preparation of the macroscopic singlet Bell state, which is pure, is completely nonpolarized, and has no polarization noise. Simultaneous fluctuation suppression in three Stokes observables below the shotnoise limit is demonstrated, opening perspectives for noiseless polarization measurements. The state is shown to be invariant to polarization transformations. This robust highly entangled isotropic state promises to fuel important applications in photonic quantum technologies.
Spectral and temporal Bloch oscillations in optical fibres
C. Bersch, G. Onishchukov, U. Peschel
APPLIED PHYSICS BLASERS AND OPTICS
104(3)
495501
(2011)

Journal
Inspired by the spacetime duality of paraxial beam diffraction and dispersive pulse spreading, the experimental implementation of a temporal equivalent of evanescently coupled waveguide arrays is demonstrated. Pulses interact with a timeperiodic potential during their propagation through an optical fibre and the generic effect of discrete diffraction is observed in time. The presented system allows fast and highresolving measurements of the complete signal evolution. To demonstrate the advanced capabilities, Bloch oscillations of an optical signal in both the time and frequency domains are realised.
Testing spectral filters as Gaussian quantum optical channels
K. Laiho, A. Christ, K. N. Cassemiro, C. Silberhorn
OPTICS LETTERS
36(8)
14761478
(2011)
We experimentally investigate the mode characteristics of multimode radiation fields propagating through frequencydependent Gaussian channels. After manipulating the twin beams emitted from a conventional parametric downconversion source via spectral filtering, we study the changes in their mode characteristics, utilizing the joint normalized correlation functions. While filtering reduces the number of spectral modes, it also leads to an apparent mode mismatch, which destroys the perfect photonnumber correlation between the twin beams, and influences the mode properties of heralded states. (c) 2011 Optical Society of America
A microcavity biosensor monitors optical resonances in microand nanostrucrtures for labelfree detection of molecules and their interactions. I will give an introduction to the field of microcavity biosensing and present an overview on the current stateofthe art. I will emphasize recent applications of optical microcavities for nanoparticle detection, trapping and manipulation, and I will highlight different modalities for ultrasensitve labelfree biosensing.
Arrayed TelecomWavelength Compatible THz nipnip Super lattice
Photomixers for Spectroscopy Applications
S. Preu, S. Bauerschmidt, S. Malzer, G. H. Doehler, H. Lu, A. C. Gossard, L. J. Wang
NATO Science for Peace and Security Series BPhysics and Biophysics
139146
(2011)

Journal
We report on the progress of roomtemperature operating, continuouswave, tunable nipnip superlattice THz photomixers, compatible with 1.55 mu m telecom laser systems. An output power of 0.65 mu W at 1 THz has been achieved at a photocurrent of 9.5 mA, using a broadband antenna. The spectral power is at a level where high resolution spectroscopy becomes attractive. This is demonstrated by measuring the absorption spectrum of water vapor between 0.4 and 1.6 THz. We constructed an array of 4 mutually coherent photomixers for higher output power and spatial resolution. The interference of the four individual beams was measured in the target plane at a standoff distance of 4.2 m. We report on both a small THz spot diameter along the array axis of < 1 cm for v > 0.3 THz and a high intensity of the central interference peak, in excellent agreement with numerical simulations. These features are very attractive for standoff imaging and spectroscopy.
Correlating internal stresses, electrical activity and defect structure
on the micrometer scale in EFG silicon ribbons
G. Sarau, S. Christiansen, M. Holla, W. Seifert
SOLAR ENERGY MATERIALS AND SOLAR CELLS
95(8)
22642271
(2011)

Journal
In the present paper, we study the influence of defects through their stress fields on the electrical activity and residual stress states of asgrown edgedefined filmfeed (EFG) multicrystalline silicon (mcSi) ribbons. We apply a combination of microRaman spectroscopy, electron beam induced current, defect etching and electron backscatter diffraction techniques that enables us to correlate internal stresses, recombination activity and microstructure on the micrometer scale. The stress fields of defect structures are considered to be too small (several tens of MPa) to influence directly the electrical activity, but they can enhance it via stressinduced accumulation of metallic impurities. It is commonly found that not all recombinationactive dislocations on grain boundaries (GBs) and within grains are accompanied by internal stresses. The reason for this is that dislocations interact with each other and tend to locally rearrange in configurations of minimum strain energy in which their stress fields can cancel partially, totally or not at all. The outcome is a nonuniform distribution of electrical activity and internal stresses along the same GB, along different GBs of similar character as well as inside the same grain and inside different grains of similar crystallographic orientations. Our work has implications for developing crystal growth procedures that may lead to reduced internal stresses and consequently to improved electrical quality and mechanical stability of mcSi materials by means of controlled interaction between structural defects. (C) 2011 Elsevier B.V. All rights reserved.
Bandgap guidance in hybrid chalcogenidesilica photonic crystal fibers
Nicolai Granzow, Patrick Uebel, Markus A. Schmidt, Andrey S. Tverjanovich, Lothar Wondraczek, Philip St J. Russell
OPTICS LETTERS
36(13)
24322434
(2011)
We report a hybrid chalcogenidesilica photonic crystal fiber made by pressureassisted meltfilling of molten glass. Photonic bandgap guidance is obtained at a silica core placed centrally in a hexagonal array of continuous centimeterslong chalcogenide strands with diameters of 1.45 mu m. In the passbands of the cladding, when the transmission through the silica core is very weak, the chalcogenide strands light up with distinct modal patterns corresponding to Mie resonances. In the spectral regions between these passbands, strong bandgap guidance is observed, where the silica core transmission loss is 60 dB/cm lower. The pressureassisted fabrication approach opens up new ways of integrating sophisticated glassbased devices into optical fiber circuitry with potential applications in supercontinuum generation, magnetooptics, wavelength selective devices, and rareearthdoped amplifiers with high gain per unit length. (C) 2011 Optical Society of America
Role of spatial coherence in GoosHanchen and ImbertFedorov shifts
Andrea Aiello, J. P. Woerdman
OPTICS LETTERS
36(16)
31513153
(2011)
We present a theory for GoosHanchen (GH) and ImbertFedorov (IF) shifts for beams of light with arbitrary spatial coherence. By applying the wellknown theory of partial spatial coherence, we can calculate explicitly spatial and angular GH and IF shifts for completely polarized beams of any shape and spatial coherence. For the specific case of a GaussSchell source, we find that only the angular part of GH and IF shifts is affected by the spatial coherence of the beam. A physical explanation of our results is given. (C) 2011 Optical Society of America
From quantum pulse gate to quantum pulse shaperengineered frequency
conversion in nonlinear optical waveguides
Benjamin Brecht, Andreas Eckstein, Andreas Christ, Hubertus Suche, Christine Silberhorn
Full control over the spatiotemporal structure of quantum states of light is an important goal in quantum optics, to generate, for instance, singlemode quantum pulses or to encode information on multiple modes, enhancing channel capacities. Quantum light pulses feature an inherent, rich spectral broadbandmode structure. In recent years, exploring the use of integrated optics as well as source engineering has led to a deep understanding of the pulsemode structure of guided quantum states of light. In addition, several groups have started to investigate the manipulation of quantum states by means of singlephoton frequency conversion. In this paper, we explore new routes towards complete control of the inherent pulsemodes of ultrafast pulsed quantum states by employing specifically designed nonlinear waveguides with adapted dispersion properties. Starting from our recently proposed quantum pulse gate (QPG), we further generalize the concept of spatiospectral engineering for arbitrary chi((2))based quantum processes. We analyse the sumfrequency generationbased QPG and introduce the differencefrequency generationbased quantum pulse shaper (QPS). Together, these versatile and robust integrated optical devices allow for arbitrary manipulations of the pulsemode structure of ultrafast pulsed quantum states. The QPG can be utilized to select an arbitrary pulse mode from a multimode input state, whereas the QPS enables the generation of specific pulse modes from an input wavepacket with a Gaussianshaped spectrum.
14 GHz visible supercontinuum generation: calibration sources for
astronomical spectrographs
S. P. Stark, T. Steinmetz, R. A. Probst, H. Hundertmark, T. Wilken, T. W. Haensch, Th. Udem, P. St. J. Russell, R. Holzwarth
We report the use of a specially designed tapered photonic crystal fiber to produce a broadband optical spectrum covering the visible spectral range. The pump source is a frequency doubled Yb fiber laser operating at a repetition rate of 14 GHz and emitting sub5 pJ pulses. We experimentally determine the optimum core diameter and achieve a 235 nm broad spectrum. Numerical simulations are used to identify the underlying mechanisms and explain spectral features. The high repetition rate makes this system a promising candidate for precision calibration of astronomical spectrographs. (C) 2011 Optical Society of America
Bellinequality tests with macroscopic entangled states of light
M. Stobinska, P. Sekatski, A. Buraczewski, N. Gisin, G. Leuchs
Quantum correlations may violate the Bell inequalities. Most experimental schemes confirming this prediction have been realized in alloptical Bell tests suffering from the detection loophole. Experiments which simultaneously close this loophole and the locality loophole are highly desirable and remain challenging. An approach to loopholefree Bell tests is based on amplification of the entangled photons (i.e., on macroscopic entanglement), for which an optical signal should be easy to detect. However, the macroscopic states are partially indistinguishable by classical detectors. An interesting idea to overcome these limitations is to replace the postselection by an appropriate preselection immediately after the amplification. This is in the spirit of state preprocessing revealing hidden nonlocality. Here, we examine one of the possible preselections, but the presented tools can be used for analysis of other schemes. Filtering methods making the macroscopic entanglement useful for Bell tests and quantum protocols are the subject of an intensive study in the field nowadays.
Superradiant Phase Transitions and the Standard Description of Circuit QED
We investigate the equilibrium behavior of a superconducting circuit QED system containing a large number of artificial atoms. It is shown that the currently accepted standard description of circuit QED via an effective model fails in an important aspect: it predicts the possibility of a superradiant phase transition, even though a full microscopic treatment reveals that a nogo theorem for such phase transitions known from cavity QED applies to circuit QED systems as well. We generalize the nogo theorem to the case of (artificial) atoms with many energy levels and thus make it more applicable for realistic cavity or circuit QED systems.
Coupled multimode optomechanics in the microwave regime
The motion of micro and nanomechanical resonators can be coupled to electromagnetic fields. This allows one to explore the mutual interaction and introduces new means to manipulate and control both light and mechanical motion. Such optomechanical systems have recently been implemented in nanoelectromechanical systems involving a nanomechanical beam coupled to a superconducting microwave resonator. Here, we propose optomechanical systems that involve multiple, coupled microwave resonators. In contrast to similar systems in the optical realm, the coupling frequency governing photon exchange between microwave modes is naturally comparable to typical mechanical frequencies. For instance this enables new ways to manipulate the microwave field, such as mechanically driving coherent photon dynamics between different modes. In particular we investigate two setups where the electromagnetic field is coupled either linearly or quadratically to the displacement of a nanomechanical beam. The latter scheme allows one to perform QND Fock state detection. For experimentally realistic parameters we predict the possibility to measure an individual quantum jump from the mechanical ground state to the first excited state. Copyright (C) EPLA, 2011
Singlemolecule imaging by optical absorption
Michele Celebrano, Philipp Kukura, Alois Renn, Vahid Sandoghdar
To date, optical studies of single molecules at room temperature have relied on the use of materials with high fluorescence quantum yield combined with efficient spectral rejection of background light. To extend singlemolecule studies to a much larger pallet of substances that absorb but do not fluoresce, scientists have explored the photothermal effect(1), interferometry(2,3), direct attenuation(4) and stimulated emission(5). Indeed, very recently, three groups have succeeded in achieving singlemolecule sensitivity in absorption(68). Here, we apply modulationfree transmission measurements known from absorption spectrometers to image single molecules under ambient conditions both in the emissive and strongly quenched states. We arrive at quantitative values for the absorption crosssection of single molecules at different wavelengths and thereby set the ground for singlemolecule absorption spectroscopy. Our work has important implications for research ranging from absorption and infrared spectroscopy to sensing of unlabelled proteins at the singlemolecule level.
Modeling of Sloped Interfaces on a Yee Grid
Dzmitry M. Shyroki
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
59(9)
32903295
(2011)

Journal
To represent material boundaries in the finitedifference timedomain or frequencydomain method, effective cell permittivity epsilon(eff) can be introduced for each grid cell crossed by material interface. In this paper we revisit the derivation of tensorial epsilon(eff) for a sloped interface, and describe possible interpolation schemes for coupling of different effective electric field and induction components near the interface. We put the resulting nonsymmetric and symmetrized effective permittivity matrices to numerical tests in the frequency domain. For veryhighcontrast interfaces the symmetrized schemes perform worse than simple staircasing while nonsymmetrized interpolation retains the secondorder convergence.
Demonstration of a ControlledPhase Gate for ContinuousVariable OneWay
Quantum Computation
Ryuji Ukai, Shota Yokoyama, Junichi Yoshikawa, Peter van Loock, Akira Furusawa
We experimentally demonstrate a controlledphase gate for continuous variables using a clusterstate resource of four optical modes. The two independent input states of the gate are coupled with the cluster in a teleportationbased fashion. As a result, one of the entanglement links present in the initial cluster state appears in the two unmeasured output modes as the corresponding entangling gate acting on the input states. The genuine quantum character of this gate becomes manifest and is verified through the presence of entanglement at the output for a product twomode coherent input state. By combining our gate with the recently reported module for singlemode Gaussian operations [R. Ukai et al., Phys. Rev. Lett. 106, 240504 (2011)], it is possible to implement any multimode Gaussian operation as a fully measurementbased oneway quantum computation.
Nonlinear Optics in GasFilled HCPCF in the Plasma Regime
P. Hoelzer, W. Chang, J. Nold, J. C. Travers, A. Nazarkin, N. Y. Joly, P. St. J. Russell
Conference on Lasers and ElectroOptics
(2011)
Laserdriven ionization in Arfilled HCPCF is accessed through selfcompression of fewmicrojoule pulses. Modeling confirms that the observed blueshifted spectral bands are caused by lightplasma interactions over an extended length in the fiber. (C)2011 Optical Society of America
Influence of ionization on ultrafast gasbased nonlinear fiber optics
W. Chang, A. Nazarkin, J. C. Travers, J. Nold, P. Hoelzer, N. Y. Joly, P. St. J. Russell
We numerically investigate the effect of ionization on ultrashort highenergy pulses propagating in gasfilled kagomelattice hollowcore photonic crystal fibers by solving an established unidirectional field equation. We consider the dynamics of two distinct regimes: ionization induced blueshift and resonant dispersive wave emission in the deepUV. We illustrate how the system evolves between these regimes and the changing influence of ionization. Finally, we consider the effect of higher ionization stages. (C) 2011 Optical Society of America
Probing multimode squeezing with correlation functions
Andreas Christ, Kaisa Laiho, Andreas Eckstein, Katiuscia N. Cassemiro, Christine Silberhorn
Broadband multimode squeezers constitute a powerful quantum resource with promising potential for different applications in quantum information technologies such as information coding in quantum communication networks or quantum simulations in higherdimensional systems. However, the characterization of a large array of squeezers that coexist in a single spatial mode is challenging. In this paper, we address this problem and propose a straightforward method for determining the number of squeezers and their respective squeezing strengths by using broadband multimode correlation function measurements. These measurements employ the large detection windows of the state of the art avalanche photodiodes in order to simultaneously probe the full Hilbert space of the generated state, which enables us to benchmark the squeezed states. Moreover, due to the structure of correlation functions, our measurements are not affected by losses. This is a significant advantage, since detectors with low efficiencies are sufficient. Our approach is less costly than tomographic methods relying on multimode homodyne detection, which is based on much more demanding measurement and analysis tools and appear to be impractical for large Hilbert spaces.
Generation of bright squeezed vacuum in the Karassiov states
M. V. Chekhova, T. Sh. Iskhakov, G. Leuchs, G. O. Rytikov
OPTICS AND SPECTROSCOPY
111(4)
565569
(2011)

Journal
We suggest an experimental procedure allowing one to prepare squeezed vacuum in a special type of generalized Bell states, first introduced by V.P. Karassiov. We present the first results on the experimental generation of such states and observation of their polarization properties.
Exact analytical representations for broadband transmission properties
of quarterwave multilayers
Victor Grigoriev, Fabio Biancalana
OPTICS LETTERS
36(19)
37743776
(2011)
The formalism of the scattering matrix is applied to describe the transmission properties of multilayered structures with deep variations of the refractive index and arbitrary arrangements of the layers. We show that there is an exact analytical formula for the transmission spectrum, which is valid for the full spectral range and which contains only a limited number of parameters for structures satisfying the quarterwave condition. These parameters are related to the poles of the scattering matrix, and we present an efficient algorithm to find them, which is based on considering the ray propagation inside the structure and subsequent application of the harmonic inversion technique. These results are significant for analyzing the reshaping of ultrashort pulses in multilayered structures. (C) 2011 Optical Society of America
Decoherence and Disorder in QuantumWalks: From Ballistic Spread to
Localization
A. Schreiber, K. N. Cassemiro, V. Potocek, A. Gabris, I. Jex, Ch. Silberhorn
We investigate the impact of decoherence and static disorder on the dynamics of quantum particles moving in a periodic lattice. Our experiment relies on the photonic implementation of a onedimensional quantum walk. The pure quantum evolution is characterized by a ballistic spread of a photon's wave packet along 28 steps. By applying controlled timedependent operations we simulate three different environmental influences on the system, resulting in a fast ballistic spread, a diffusive classical walk, and the first Anderson localization in a discrete quantum walk architecture.
Optofluidic refractiveindex sensor in stepindex fiber with parallel
hollow microchannel
H. W. Lee, M. A. Schmidt, P. Uebel, H. Tyagi, N. Y. Joly, M. Scharrer, P. St. J. Russell
We present a simple refractive index sensor based on a stepindex fiber with a hollow microchannel running parallel to its core. This channel becomes waveguiding when filled with a liquid of index greater than silica, causing sharp dips to appear in the transmission spectrum at wavelengths where the glasscore mode phasematches to a mode of the liquidcore. The sensitivity of the dipwavelengths to changes in liquid refractive index is quantified and the results used to study the dynamic flow characteristics of fluids in narrow channels. Potential applications of this fiber microstructure include measuring the optical properties of liquids, refractive index sensing, biophotonics and studies of fluid dynamics on the nanoscale. (C) 2011 Optical Society of America
Dynamical entanglement purification using chains of atoms and optical
cavities
In the framework of cavity QED, we propose a practical scheme to purify dynamically a bipartite entangled state using short chains of atoms coupled to highfinesse optical cavities. In contrast to conventional entanglement purification protocols, we avoid controlledNOT gates, thus reducing complicated pulse sequences and superfluous qubit operations. Our interaction scheme works in a deterministic way and, together with entanglement distribution and swapping, opens a route toward efficient quantum repeaters for longdistance quantum communication.
Photoluminescence of samples produced by electroless wet chemical
etching: Between silicon nanowires and porous structures
Felix Voigt, Vladimir Sivakov, Viktor Gerliz, Gottfried H. Bauer, Bjoern Hoffmann, Gyorgy Z. Radnoczi, Bela Pecz, Silke Christiansen
PHYSICA STATUS SOLIDI AAPPLICATIONS AND MATERIALS SCIENCE
208(4)
893899
(2011)

Journal
Samples containing silicon nanowires (SiNWs) and highly porous structures (PSi) were prepared by electroless wet chemical etching (EWCE) of crystalline silicon wafers using various etching parameters. Photoluminescence (PL) measurements were performed with excitation at 488 nm and a photon energy flux of 337mWcm (2). According to the diameters of the SiNWs (> 10 nm), from quantum confinement (QC) theory no shift in PL peak energy compared to the bandgap of crystalline silicon is expected. However, PL measurements show peak emission energies ranging between 1.4 and 1.6 eV. After further treatment of the samples with HF, substantial PL emission was still detectable with the measured PL peak pinned at 1.4 eV irrespective of etching time. We explain the observations by the hypothesis that the persistent part of PL emission is generated by nanocrystals located at the rough sidewalls of the SiNWs or residing within the porous sample structure. The part of the PL, which was present before HF treatment, but vanished after the treatment, is attributed to the presence of silicon suboxide surrounding the SiNWs or covering other Si surfaces. This hypothesis is explored by means of three sample series, prepared with different preparation parameters. In the first series the time used during the initial metallization step in order to prepare an Ag nanoparticle layer on the top surface was varied, in the second series the etching time was the changed parameter and in the third series the HF to H(2)O(2) concentration ratio was varied.
[GRAPHICS]
Strong visible orange colored PL of a sample produced by EWCE starting from a heavily doped wafer (ntype cSi (111), As as dopant) and excited at 337 nm ( the sample was mounted on a glass substrate. Blue luminescence is due to the substrate). (C) 2011 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim
Interaction of highly focused vector beams with a metal knifeedge
P. Marchenko, S. Orlov, C. Huber, P. Banzer, S. Quabis, U. Peschel, G. Leuchs
We investigate the interaction of highly focused linearly polarized optical beams with a metal knifeedge both theoretically and experimentally. A high numerical aperture objective focusses beams of various wavelengths onto samples of different subwavelength thicknesses made of several opaque and pure materials. The standard evaluation of the experimental data shows material and sample dependent spatial shifts of the reconstructed intensity distribution, where the orientation of the electric field with respect to the edge plays an important role. A deeper understanding of the interaction between the knifeedge and the incoming highly focused beam is gained in our theoretical model by considering eigenmodes of the metalinsulatormetal structure. We achieve good qualitative agreement of our numerical simulations with the experimental findings. (C) 2011 Optical Society of America
Supercontinuum generation in chalcogenidesilica stepindex fibers
N. Granzow, S. P. Stark, M. A. Schmidt, A. S. Tverjanovich, L. Wondraczek, P. St. J. Russell
We explore the use of a highly nonlinear chalcogenidesilica waveguide for supercontinuum generation in the near infrared. The structure was fabricated by a pressureassisted meltfilling of a silica capillary fiber (1.6 mu m bore diameter) with Ga4Ge21Sb10S65 glass. It was designed to have zero group velocity dispersion (for HE11 core mode) at 1550 nm. Pumping a 1 cm length with 60 fs pulses from an erbiumdoped fiber laser results in the generation of octavespanning supercontinuum light for pulse energies of only 60 pJ. Good agreement is obtained between the experimental results and theoretical predictions based on numerical solutions of the generalized nonlinear Schrodinger equation. The pressureassisted meltfilling approach makes it possible to realize highly nonlinear devices with unusual combinations of materials. For example, we show numerically that a 1 cm long As2S3:silica stepindex fiber with a core diameter of 1 mu m, pumped by 60 fs pulses at 1550 nm, would generate a broadband supercontinuum out to 4 mu m. (C) 2011 Optical Society of America
Interfacial reactions between tellurite melts and silica during the
production of microstructured optical devices
N. Da, A. A. Enany, N. Granzow, M. A. Schmidt, P. St. J. Russell, L. Wondraczek
JOURNAL OF NONCRYSTALLINE SOLIDS
357(67)
15581563
(2011)

Journal
Interfacial reactions between silica glass and tellurite melts were studied under confined conditions in the temperature regime of 400700 degrees C, applying two different sampling techniques: isothermal heattreatment of a several micrometer thick tellurite film, confined in a silica/tellurite/silica sandwich, and capillary filling of tellurite melts into silica microcapillaries. The sandwich technique provides detailed ex situ insights on the interface chemistry, microstructure and diffusion after given treatment times and temperatures. Data on dynamic viscosity, surface tension, wetting behaviour and eventual scaling effects was obtained from the capillary filling technique. For temperatures > 500 degrees C, silica is completely wet by the considered tellurite melts. At T > 600 degrees C and for a treatment time of 20 min or longer, cationic diffusion of Na(+) and Te(4+) into the silica substrate occurs to a depth of several micrometers. At the same time, the tellurite melt attacks the silica surface, leading to the formation of a stationary silicatellurite reaction layer and silica dissolution. Dissolved silica was observed to reprecipitate from the tellurite melt by liquidliquid phase separation. In the early reaction stages, as a result of alkali diffusion into the silica substrate, betaquartz crystallizes at the interface (what can be avoided by using alkalifree filling glasses). Obtained data set the boundary conditions for the generation of telluritesilica allsolid fiber waveguides by melt infiltration of silica photonic crystal fibers or microcapillaries. (C) 2011 Elsevier B.V. All rights reserved.
Photoluminescence and Raman Scattering in Arrays of Silicon Nanowires
V. Yu. Timoshenko, K. A. Gonchar, L. A. Golovan, A. I. Efimova, V. A. Sivakov, A. Dellith, S. H. Christiansen
JOURNAL OF NANOELECTRONICS AND OPTOELECTRONICS
6(4)
519524
(2011)

Journal
Arrays of silicon (Si) nanowires with mean diameters of about 50100 nm formed by wetchemical etching of crystalline silicon wafers with low and high doping levels were investigated by means of photoluminescence and Raman spectroscopy. The photoluminescence bands in the spectral ranges of 650900 nm and about 1100 nm were detected and explained by the radiative recombination of excitons confined in Si nanocrystals on the surface of Si nanowires and by the interband photoluminescence in the volume of Si nanowires, respectively. The intensities of the bandgap related photoluminescence and Raman scattering under excitation at 1064 nm were significantly larger for the Si nanowire samples in comparison with that for the crystalline Si substrates. This fact is explained by strong scattering of the excitation light, which results in partial light trapping in silicon nanowire arrays. The doping level and surface orientation of the substrate were found to influence the photoluminescence and Raman scattering in Si nanowire arrays.
Discontinuous space variant subwavelength structures for generating
radially polarized light in visible region
Z. Ghadyani, S. Dmitriev, N. Lindlein, G. Leuchs, O. Rusina, I. Harder
JOURNAL OF THE EUROPEAN OPTICAL SOCIETYRAPID PUBLICATIONS
6
11041
(2011)

Journal
A discontinuous space variant subwavelength dielectric grating is designed and fabricated for generating radially polarized light in visible region (lambda = 632.8 nm). The design is based on subwavelength silicon nitride structures introducing a retardation of pi/2 by form birefringence, with space variant orientation of the optical axis. The pattern is divided into concentric ring segments with constant structural parameters, therefore reducing electronbeam writing time significantly. The design avoids the technological challenges encountered in the generation of a continuous space variant grating while maintaining good quality of the resulting polarization mode. [DOI: http://dx.doi.org/10.2971/jeos.2011.11041]
Comparison Between an Analytical Asymptotic Fiber Drawing Model With
Full NavierStokes Solution Taking Into Account the Effects of Inner
Pressure and Surface Tension
Giovanni Luzi, Philipp Epple, Michael Scharrer, Ken Fujimoto, Cornelia Rauh, Antonio Delgado
JOURNAL OF LIGHTWAVE TECHNOLOGY
29(11)
16381646
(2011)

Journal
A fluidmechanics model that make use of asymptotic analysis based on small aspect ratio of capillaries has been compared with the full 3D set of the N.St. equations, for modelling the fabrication of capillary tubes. The final asymptotic equations are solved numerically and then compared with the N.St. solutions, obtained with a commercial finite elements solver. The present paper focuses on the comparison of the solution of the two methods taking into account the effects of surface tension and internal hole pressure, since those are of essential importance during drawing. It is shown that the analytical asymptotic method delivers reliable results for practical applications, as long as the inner pressure or the temperature does not exceed too high values.
Toward Local Growth of Individual Nanowires on ThreeDimensional
Microstructures by Using a Minimally Invasive Catalyst Templating Method
Martin Guenter Jenke, Damiana Lerose, Christoph Niederberger, Johann Michler, Silke Christiansen, Ivo Utke
We present a novel minimally invasive postprocessing method for catalyst templating based on focused charged particle beam structuring, which enables a localized vapor liquid solid (VLS) growth of individual nanowires on prefabricated threedimensional micro and nanostructures. Gasassisted focused electron beam induced deposition (FEBID) was used to deposit a SiO(x) surface layer of about 10 x 10 mu m(2) on top of a silicon atomic force microscopy cantilever. Gallium focused ion beam (FIB) milling was used to make a hole through the SiO(x) layer into the underlying silicon. The hole was locally filled with a gold catalyst via FEBID using either Me(2)Au(tfac) or Me(2)Au(acac) as precursor. Subsequent chemical vapor deposition (CVD)induced VLS growth using a mixture of SiH(4) and Ar resulted in individual high quality crystalline nanowires. The process, its yield, and the resulting angular distribution/crystal orientation of the silicon nanowires are discussed. The presented combined FIB/FEBID/CVDVLS process is currently the only proven method that enables the growth of individual monocrystalline Si nanowires on prestructured substrates and devices.
Optical antennas for modifying the radiation of single quantum emitters
We discuss the use of optical antennas for the modification of the radiative properties of single emitters such as organic molecules. In particular, we report on our experimental results regarding the modification of the spontaneous emission and excitation rates, as well as the emission spectrum and directionality of single fluorescent molecules in the vicinity of plasmonic nanostructures. Furthermore, we present novel dielectric and metallodielectric planar antennas for bundling the emission of an emitter into a welldefined mode, leading to collection efficiencies up to 99% for the emitted single photons.
Efficient heralding of photonic qubits with applications to
deviceindependent quantum key distribution
David Pitkanen, Xiongfeng Ma, Ricardo Wickert, Peter van Loock, Norbert Luetkenhaus
We present an efficient way of heralding photonic qubit signals using linear optics devices. First, we show that one can obtain asymptotically perfect heralding and unit success probability with growing resources. Second, we show that even using finite resources, we can improve qualitatively and quantitatively over earlier heralding results. In the latter scenario, we can obtain perfect heralded photonic qubits while maintaining a finite success probability. We demonstrate the advantage of our heralding scheme by predicting key rates for deviceindependent quantum key distribution, taking imperfections of sources and detectors into account.
Geometric Spin Hall Effect of Light at polarizing interfaces
J. Korger, A. Aiello, C. Gabriel, P. Banzer, T. Kolb, C. Marquardt, G. Leuchs
APPLIED PHYSICS BLASERS AND OPTICS
102(3)
427432
(2011)

Journal
The geometric Spin Hall Effect of Light (geometric SHEL) amounts to a polarizationdependent positional shift when a light beam is observed from a reference frame tilted with respect to its direction of propagation. Motivated by this intriguing phenomenon, the energy density of the light beam is decomposed into its Cartesian components in the tilted reference frame. This illustrates the occurrence of the characteristic shift and the significance of the effective response function of the detector.
We introduce the concept of a tilted polarizing interface and provide a scheme for its experimental implementation. A light beam passing through such an interface undergoes a shift resembling the original geometric SHEL in a tilted reference frame. This displacement is generated at the polarizer and its occurrence does not depend on the properties of the detection system. We give explicit results for this novel type of geometric SHEL and show that at grazing incidence this effect amounts to a displacement of multiple wavelengths, a shift larger than the one introduced by GoosHanchen and ImbertFedorov effects.
Experimental crosspolarization detection of coupling farfield light to
highly confined plasmonic gap modes via nanoantennas
J. Wen, P. Banzer, A. Kriesch, D. Ploss, B. Schmauss, U. Peschel
We experimentally demonstrate the coupling of farfield light to highly confined plasmonic gap modes via connected nanoantennas. The excitation of plasmonic gap modes is shown to depend on the polarization, position, and wavelength of the incident beam. Farfield measurements performed in crossed polarization allow for the detection of extremely weak signals reemitted from gap waveguides and can increase the signaltonoise ratio dramatically. (C) 2011 American Institute of Physics. [doi:10.1063/1.3564904]
Controlling the Phase of a Light Beam with a Single Molecule
M. Pototschnig, Y. Chassagneux, J. Hwang, G. Zumofen, A. Renn, Vahid Sandoghdar
We employ heterodyne interferometry to investigate the effect of a single organic molecule on the phase of a propagating laser beam. We report on the first phasecontrast images of individual molecules and demonstrate a singlemolecule electrooptical phase switch by applying a voltage to the microelectrodes embedded in the sample. Our results may find applications in singlemolecule holography, fast optical coherent signal processing, and singleemitter quantum operations.
Permanent bending and alignment of ZnO nanowires
Christian Borschel, Susann Spindler, Damiana Lerose, Arne Bochmann, Silke H. Christiansen, Sandor Nietzsche, Michael Oertel, Carsten Ronning
Ion beams can be used to permanently bend and realign nanowires after growth. We have irradiated ZnO nanowires with energetic ions, achieving bending and alignment in different directions. Not only the bending of single nanowires is studied in detail, but also the simultaneous alignment of large ensembles of ZnO nanowires. Computer simulations reveal how the bending is initiated by ion beam induced damage. Detailed structural characterization identifies dislocations to relax stresses and make the bending and alignment permanent, even surviving annealing procedures.
Chemical and optical characterisation of atomic layer deposition
aluminium doped ZnO films for photovoltaics by glow discharge optical
emission spectrometry
S. W. Schmitt, G. Gamez, V. Sivakov, M. Schubert, S. H. Christiansen, J. Michler
JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY
26(4)
822827
(2011)

Journal
Aluminium doped ZnO (AZO) alloy films produced by atomic layer deposition (ALD) are analysed by glow discharge optical emission spectrometry (GDOES). A measurement procedure is established, to determine simultaneously thickness, mean chemical composition and refractive index of homogeneous films using GDOES and profilometry measurements. The GDOES measured Al contents of the AZO films lie below those expected for the realised ALD cycles. Determined refractive indices are of the same accuracy as ellipsometry measurements and are dependent on the film composition as well as on the wavelength of the spectral lines used for analysis. The findings support the use of GDOES as an analysis technique in the development of photovoltaic thin films.
Hybrid squeezing of solitonic resonant radiation in photonic crystal
fibers
Truong X. Tran, Katiuscia N. Cassemiro, Christoph Soeller, Keith J. Blow, Fabio Biancalana
We report the existence of a kind of squeezing in photonic crystal fibers which is conceptually intermediate between fourwavemixinginduced squeezing in which all the participant waves are monochromatic waves, and selfphasemodulationinduced squeezing for a single pulse in a coherent state. This hybrid squeezing occurs when an arbitrary short soliton emits quasimonochromatic resonant radiation near a zerogroupvelocitydispersion point of the fiber. Photons around the resonant frequency become strongly correlated due to the presence of the classical soliton, and a reduction of the quantum noise below the shotnoise level is predicted.
Bubble formation in basaltlike melts
Martin Jensen, Yuanzheng Yue, Ralf Keding
GLASS TECHNOLOGYEUROPEAN JOURNAL OF GLASS SCIENCE AND TECHNOLOGY PART A
52(4)
127135
(2011)
The effect of the melting temperature on bubble size and bubble formation in an iron bearing calcium aluminosilicate melt is studied by means of indepth images acquired by optical microscopy. The bubble size distribution and the total bubble volume are determined by counting the number of bubbles and their diameter. The variation in melting temperature has little influence on the overall bubble volume. However, the size distribution of the bubbles varies with the melting temperature. When the melt is slowly cooled, the bubble volume increases, implying decreased solubility of the gaseous species. Mass spectroscopy analysis of gases liberated during heating of the glass reveals that small bubbles contain predominantly CH4, CO and CO2, whereas large bubbles contain N2, SO2 and H2S. The methodology utilised in this work can, besides mapping the bubbles in a glass, be applied to shed light on the sources of bubble formation.
A precise optical determination of nanoscale diameters of semiconductor
nanowires
G. Broenstrup, C. Leiterer, N. Jahr, C. Gutsche, A. Lysov, I. Regolin, W. Prost, F. J. Tegude, W. Fritzsche, S. Christiansen, et al.
Electrical and optical properties of semiconducting nanowires (NWs) strongly depend on their diameters. Therefore, a precise knowledge of their diameters is essential for any kind of device integration. Here, we present an optical method based on dark field optical microscopy to easily determine the diameters of individual NWs with an accuracy of a few nanometers and thus a relative error of less than 10%. The underlying physical principle of this method is that strong Mie resonances dominate the optical scattering spectra of most semiconducting NWs and can thus be exploited. The feasibility of this method is demonstrated using GaAs NWs but it should be applicable to most types of semiconducting NWs as well. Dark field optical microscopy shows that even slight tapering of the NWs, i.e. diameter variations of a few nanometers, can be detected by a visible color change. Abrupt diameter changes of a few nanometers, as they occur for example when growth conditions vary, can be determined as well. In addition a profound analysis of the elastic scattering properties of individual GaAs NWs is presented theoretically using Mie calculations as well as experimentally by dark field microscopy. This method has the advantage that no vacuum technique is needed, a fast and reliable analysis is possible based on cheap standard hardware.
This article reviews recent hybrid approaches to optical quantum information processing, in which both discrete and continuous degrees of freedom are exploited. There are wellknown limitations to optical singlephotonbased qubit and multiphotonbased qumode implementations of quantum communication and quantum computation, when the toolbox is restricted to the most practical set of linear operations and resources such as linear optics and Gaussian operations and states. The recent hybrid approaches aim at pushing the feasibility, the efficiencies, and the fidelities of the linear schemes to the limits, potentially adding weak or measurementinduced nonlinearities to the toolbox.
We consider entanglement swapping with general mixed twomode Gaussian states and calculate the optimal gains for a broad class of such states including those states most relevant in communication scenarios. We show that, for this class of states, entanglement swapping adds no additional mixedness; that is, the ensembleaverage output state has the same purity as the input states. This implies that, by using intermediate entanglement swapping steps, it is, in principle, possible to distribute entangled twomode Gaussian states of higher purity as compared to direct transmission. We then apply the general results on optimal Gaussian swapping to the problem of quantum communication over a lossy fiber and demonstrate that, in contrast to the negative conclusions in the literature, swappingbased schemes in fact often perform better than direct transmission for high input squeezing. However, an effective transmission analysis reveals that the hope for improved performance based on optimal Gaussian entanglement swapping is spurious since the swapping does not lead to an enhancement of the effective transmission. This implies that the same or better results can always be obtained using direct transmission in combination with, in general, less squeezing.
Collective Dynamics in Optomechanical Arrays
Georg Heinrich, Max Ludwig, Jiang Qian, Bjoern Kubala, Florian Marquardt
Optomechanical systems couple light stored inside an optical cavity to the motion of a mechanical mode. Recent experiments have demonstrated setups, such as photonic crystal structures, that in principle allow one to confine several optical and vibrational modes on a single chip. Here we start to investigate the collective nonlinear dynamics in arrays of coupled optomechanical cells. We show that such "optomechanical arrays" can display synchronization, and that they can be described by an effective Kuramototype model.
Doppler velocimetry on microparticles trapped and propelled by laser
light in liquidfilled photonic crystal fiber
M. K. Garbos, T. G. Euser, O. A. Schmidt, S. Unterkofler, P. St. J. Russell
OPTICS LETTERS
36(11)
20202022
(2011)
Laser Doppler velocimetry is used to measure very accurately the velocity and position of a microparticle propelled and guided by laser light in liquidfilled photonic crystal fiber. Periodic variations in particle velocity are observed that correlate closely with modal beating between the two lowest order guided fiber modes. (C) 2011 Optical Society of America
Using Saturation Effects in a Nonlinear Amplifying Loop Mirror for
Multilevel PhasePreserving Amplitude Regeneration
Tobias Roethlingshoefer, Georgy Onishchukov, Bernhard Schmauss, Gerd Leuchs
2011 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS
(ICTON)
(2011)
The influence of amplifier gain saturation in nonlinear amplifying loop mirror on simultaneous phasepreserving regeneration of two power states has been studied. Numerical simulations have shown an improvement of up to 4 dB for the first, lowpower state and 8 dB for the second highpower state. Compared to the linear amplifier case an improvement of 3 dB for the second power state has been achieved.
Resonant selfpulsations in coupled nonlinear microcavities
A different point of view on the phenomenon of selfpulsations is presented, which shows that they are a balanced state formed by two counteracting processes: beating of modes and bistable switching. A structure based on two coupled nonlinear microcavities provides a generic example of a system with enhanced ability to support this phenomenon. The specific design of such a structure in the form of multilayered media is proposed, and the coupledmode theory is applied to describe its dynamical properties. It is emphasized that the frequency of selfpulsations is related to the frequency splitting between resonant modes and can be adjusted over a broad range.
Gain Enhancement by Dielectric Horns in the Terahertz Band
Belen AndresGarcia, Enrique GarciaMunoz, Sebastian Bauerschmidt, Sascha Preu, Stefan Malzer, Gottfried H. Doehler, Lijun Wang, Daniel SegoviaVargas
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
59(9)
31643170
(2011)

Journal
A new geometry for the design of antennas in the Terahertz band is presented. The structure is based on a horn antenna etched in the substrate and fed with a planar printed antenna used for generation of terahertz radiation, designed for the 200 GHz to 3 THz range. For the proposed antenna, the energy distribution through the substrate is reduced towards an increase in the gain of the system, at least, 8 dB in a 1: 10 bandwidth. The structure has been measured showing the expected behavior in the low band.
A calibration method for broadbandwidth cavity enhanced absorption
spectroscopy performed with supercontinuum radiation
T. Laurila, I. S. Burns, J. Hult, J. H. Miller, C. F. Kaminski
APPLIED PHYSICS BLASERS AND OPTICS
102(2)
271278
(2011)

Journal
An efficient calibration method has been developed for broadbandwidth cavity enhanced absorption spectroscopy. The calibration is performed using phase shift cavity ringdown spectroscopy, which is conveniently implemented through use of an acoustooptic tunable filter (AOTF). The AOTF permits a narrowband portion of the SC spectrum to be scanned over the full highreflectivity bandwidth of the cavity mirrors. After calibration the AOTF is switched off and broadbandwidth CEAS can be performed with the same light source without any loss of alignment to the setup. We demonstrate the merits of the method by probing transitions of oxygen molecules O(2) and collisional pairs of oxygen molecules (O(2))(2) in the visible spectral range.
Understanding the dynamics of photoionizationinduced nonlinear effects
and solitons in gasfilled hollowcore photonic crystal fibers
We present the details of our previously formulated model [Saleh et al., Phys. Rev. Lett. 107, 203902 (2011)] that governs pulse propagation in hollowcore photonic crystal fibers filled by an ionizable gas. By using perturbative methods, we find that the photoionization process induces the opposite phenomenon of the wellknown Raman selffrequency redshift of solitons in solidcore glass fibers, as was recently experimentally demonstrated [Holzer et al., Phys. Rev. Lett. 107, 203901 (2011)]. This process is only limited by ionization losses, and leads to a constant acceleration of solitons in the time domain with a continuous blueshift in the frequency domain. By applying the GagnonBelanger gauge transformation, multipeak "inverted gravitylike" solitary waves are predicted. We also demonstrate that the pulse dynamics shows the ejection of solitons during propagation in such fibers, analogous to what happens in conventional solidcore fibers. Moreover, unconventional longrange nonlocal interactions between temporally distant solitons, unique of gas plasma systems, are predicted and studied. Finally, the effects of higherorder dispersion coefficients and the shock operator on the pulse dynamics are investigated, showing that the conversion efficiency of resonant radiation into the deep UV can be improved via plasma formation.
99% efficiency in collecting photons from a single emitter
XueWen Chen, Stephan Goetzinger, Vahid Sandoghdar
OPTICS LETTERS
36(18)
35453547
(2011)
In a previous paper [Nat. Photon. 5, 166 ( 2011)], we reported on a planar dielectric antenna that achieved 96% efficiency in collecting the photons emitted by a single molecule. In that work, the transition dipole moment of the molecule was set perpendicular to the antenna plane. Here, we present a theoretical extension of that scheme that reaches collection efficiencies beyond 99% for emitters with arbitrarily oriented dipole moments. Our work opens important doors in a wide range of contexts including quantum optics, quantum metrology, nanoanalytics, and biophysics. In particular, we provide antenna parameters to realize ultrabright singlephoton sources in highindex materials such as semiconductor quantum dots and color centers in diamond, as well as sensitive detection of single molecules in nanofluidic devices. (C) 2011 Optical Society of America
Birefringence and dispersion of cylindrically polarized modes in
nanobore photonic crystal fiber
T. G. Euser, M. A. Schmidt, N. Y. Joly, C. Gabriel, C. Marquardt, L. Y. Zang, M. Foertsch, P. Banzer, A. Brenn, D. Elser, et al.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA BOPTICAL PHYSICS
28(1)
193198
(2011)

Journal
We demonstrate experimentally and theoretically that a nanoscale hollow channel placed centrally in the solidglass core of a photonic crystal fiber strongly enhances the cylindrical birefringence (the modal index difference between radially and azimuthally polarized modes). Furthermore, it causes a large split in group velocity and group velocity dispersion. We show analytically that all three parameters can be varied over a wide range by tuning the diameters of the nanobore and the core. (C) 2010 Optical Society of America
Disentanglement in bipartite continuousvariable systems
F. A. S. Barbosa, A. J. de Faria, A. S. Coelho, K. N. Cassemiro, A. S. Villar, P. Nussenzveig, M. Martinelli
Entanglement in bipartite continuousvariable systems is investigated in the presence of partial losses such as those introduced by a realistic quantum communication channel, e. g., by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situation reminiscent of socalled entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined, and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuousvariable entanglement in more complex multipartite systems.
Graphical calculus for Gaussian pure states
Nicolas C. Menicucci, Steven T. Flammia, Peter van Loock
We provide a unified graphical calculus for all Gaussian pure states, including graph transformation rules for all local and semilocal Gaussian unitary operations, as well as local quadrature measurements. We then use this graphical calculus to analyze continuousvariable (CV) cluster states, the essential resource for oneway quantum computing with CV systems. Current graphical approaches to CV cluster states are only valid in the unphysical limit of infinite squeezing, and the associated graph transformation rules only apply when the initial and final states are of this form. Our formalism applies to all Gaussian pure states and subsumes these rules in a natural way. In addition, the term "CV graph state" currently has several inequivalent definitions in use. Using this formalism we provide a single unifying definition that encompasses all of them. We provide many examples of how the formalism may be used in the context of CV cluster states: defining the "closest" CV cluster state to a given Gaussian pure state and quantifying the error in the approximation due to finite squeezing; analyzing the optimality of certain methods of generating CV cluster states; drawing connections between this graphical formalism and bosonic Hamiltonians with Gaussian ground states, including those useful for CV oneway quantum computing; and deriving a graphical measure of bipartite entanglement for certain classes of CV cluster states. We mention other possible applications of this formalism and conclude with a brief note on fault tolerance in CV oneway quantum computing.
Pressureassisted meltfilling and optical characterization of Au
nanowires in microstructured fibers
H. W. Lee, M. A. Schmidt, R. F. Russell, N. Y. Joly, H. K. Tyagi, P. Uebel, P. St. J. Russell
We report a novel splicingbased pressureassisted meltfilling technique for creating metallic nanowires in hollow channels in microstructured silica fibers. Wires with diameters as small as 120 nm (typical aspect ration 50:1) could be realized at a filling pressure of 300 bar. As an example we investigate a conventional singlemode stepindex fiber with a parallel gold nanowire (wire diameter 510 nm) running next to the core. Optical transmission spectra show dips at wavelengths where guided surface plasmon modes on the nanowire phase match to the glass core mode. By monitoring the sidescattered light at narrow breaks in the nanowire, the loss could be estimated. Values as low as 0.7 dB/mm were measured at resonance, corresponding to those of an ultralongrange eigenmode of the glasscore/nanowire system. By thermal treatment the hollow channel could be collapsed controllably, permitting creation of a conical gold nanowire, the optical properties of which could be monitored by sidescattering. The reproducibility of the technique and the high optical quality of the wires suggest applications in fields such as nonlinear plasmonics, nearfield scanning optical microscope tips, cylindrical polarizers, optical sensing and telecommunications. (C) 2011 Optical Society of America
Highly efficient and isotope selective photoionization of barium atoms
using diode laser and LED light
We demonstrated a simple method to photoionize barium atoms using 791 nm diode laser together with 310 nm UV LED. It solved the bottleneck problem of previous method using 791 nm diode laser and 337 nm N2 laser, whose ionization rate was limited by the repetition rate of N2 laser. Compared with previous method, it has advantages of high efficiency together with simple and cheap setups. By tuning the frequency of 791 nm laser to be resonant with the desired isotope, isotope selective photoionization has been realized. (C) 2011 Optical Society of America
Tunable, continuouswave Terahertz photomixer sources and applications
S. Preu, G. H. Doehler, S. Malzer, L. J. Wang, A. C. Gossard
JOURNAL OF APPLIED PHYSICS
109(6)
061301
(2011)

Journal
This review is focused on the latest developments in continuouswave (CW) photomixing for Terahertz (THz) generation. The first part of the paper explains the limiting factors for operation at high frequencies similar to 1 THz, namely transit time or lifetime rolloff, antenna (R)device (C) RC rolloff, current screening and blocking, and heat dissipation. We will present various realizations of both photoconductive and pin diodebased photomixers to overcome these limitations, including perspectives on novel materials for highpower photomixers operating at telecom wavelengths (1550 nm). In addition to the classical approach of feeding current originating from a small semiconductor photomixer device to an antenna (antennabased emitter, AE), an antennaless approach in which the active area itself radiates (large area emitter, LAE) is discussed in detail. Although we focus on CW photomixing, we briefly discuss recent results for LAEs under pulsed conditions. Record power levels of 1.5 mW average power and conversion efficiencies as high as 2 x 10(3) have been reached, about 2 orders of magnitude higher than those obtained with CW antennabased emitters. The second part of the paper is devoted to applications for CW photomixers. We begin with a discussion of the development of novel THz optics. Special attention is paid to experiments exploiting the long coherence length of CW photomixers for coherent emission and detection of THz arrays. The long coherence length comes with an unprecedented narrow linewidth. This is of particular interest for spectroscopic applications, the field in which THz research has perhaps the highest impact. We point out that CW spectroscopy systems may potentially be more compact, cheaper, and more accurate than conventional pulsed systems. These features are attributed to telecomwavelength compatibility, to excellent frequency resolution, and to their huge spectral density. The paper concludes with prototype experiments of THz wireless LAN applications. For future telecommunication systems, the limited bandwidth of photodiodes is inadequate for further upshifting carrier frequencies. This, however, will soon be required for increased data throughput. The implementation of telecomwavelength compatible photomixing diodes for downconversion of an optical carrier signal to a (sub) THz RF signal will be required. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552291]
Concentric ring metal grating for generating radially polarized light
Z. Ghadyani, I. Vartiainen, I. Harder, W. Iff, A. Berger, N. Lindlein, M. Kuittinen
A subwavelength concentric ring metal grating for visible light (lambda  632.8 nm) is designed and fabricated by electronbeam lithography to transform circularly polarized light into radially polarized light. Experimental results are compared to theoretical predictions and the advantages and disadvantages of the element with alternative methods are discussed. (C) 2011 Optical Society of America
Diffractive simultaneous bidirectional shearing interferometry using
tailored spatially coherent light
Vanusch Nercissian, Irina Harder, Klaus Mantel, Andreas Berger, Gerd Leuchs, Norbert Lindlein, Johannes Schwider
Measurements of wavefront deformations can be carried out with the help of lateral shearing interferometers. Here the focus is on a setup providing two shears along orthogonal directions simultaneously to generate the data needed for a reconstruction. We describe a diffractive solution using Ronchi phase gratings with a suppressed zeroth order for both the doubling of the wavefront under test and the bidirectional shearing unit. A series arrangement of the gratings offers an onaxis geometry, which minimizes the systematic errors of the test. For illumination, an extended incoherent monochromatic light source is used. Highcontrast fringes can be obtained by tailoring the degree of coherence via a periodic intensity distribution. (c) 2011 Optical Society of America
Improved rubidium atomic beam clock based on lamppumping and
fluorescencedetection scheme
Y. H. Wang, J. Q. Huang, Y. Gu, S. Q. Liu, T. Q. Dong, Z. H. Lu
JOURNAL OF THE EUROPEAN OPTICAL SOCIETYRAPID PUBLICATIONS
6
11005
(2011)

Journal
A compact, portable rubidium atomic beam clock based on lamppumping and fluorescencedetection scheme is proposed. The expected shortterm frequency stability can be at least three orders of magnitude better than that of previous experimental results. The usages of lamp pumping, fluorescence detection and microwave slowwave resonance structures make this design robust and compact. [DOI: 10.2971/jeos.2011.11005]
Ultrafast nonlinear optics in gasfilled hollowcore photonic crystal
fibers [Invited]
John C. Travers, Wonkeun Chang, Johannes Nold, Nicolas Y. Joly, Philip St. J. Russell
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA BOPTICAL PHYSICS
28(12)
A11A26
(2011)
We review the use of hollowcore photonic crystal fibers (PCFs) in the field of ultrafast gasbased nonlinear optics, including recent experiments, numerical modeling, and a discussion of future prospects. Concentrating on broadband guiding kagomestyle hollowcore PCF, we describe its potential for moving conventional nonlinear fiber optics both into extreme regimessuch as fewcycle pulse compression and efficient deep ultraviolet wavelength generationand into regimes hitherto inaccessible, such as singlemode guidance in a photoionized plasma and highharmonic generation in fiber. (C) 2011 Optical Society of America
QUANTUM MECHANICS The gentle cooling touch of light
Laser light has been used to cool a nanomechanical resonator to its lowest energy state. The result opens the door to testing the principles of quantum mechanics and to applications in quantum information processing.
Plasmonic Photonic Crystal Fiber
M. A. Schmidt, H. Lee, H. Tyagi, P. Uebel, P. St J. Russell
Conference on Lasers and ElectroOptics
(2011)
We review our results of metalized hybrid photonic crystal fibers. We explain the important properties of spiralling plasmons on wires and in arrays and discuss our main experimental achievements such as excitation of superplasmon modes. (C) 2010 Optical Society of America
Femtosecond Nonlinear Fiber Optics in the Ionization Regime
P. Hoelzer, W. Chang, J. C. Travers, A. Nazarkin, J. Nold, N. Y. Joly, M. F. Saleh, F. Biancalana, P. St. J. Russell
By using a gasfilled kagomestyle photonic crystal fiber, nonlinear fiber optics is studied in the regime of optically induced ionization. The fiber offers low anomalous dispersion over a broad bandwidth and low loss. Sequences of blueshifted pulses are emitted when 65 fs, fewmicrojoule pulses, corresponding to highorder solitons, are launched into the fiber and undergo selfcompression. The experimental results are confirmed by numerical simulations which suggest that freeelectron densities of similar to 10(17) cm(3) are achieved at peak intensities of 10(14) W/cm(2) over length scales of several centimeters.
Nonreciprocal switching thresholds in coupled nonlinear microcavities
Victor Grigoriev, Fabio Biancalana
OPTICS LETTERS
36(11)
21312133
(2011)
A concept for the design of nonlinear optical diodes is proposed that uses the multistability of coupled nonlinear microcavities and the dependence of switching thresholds on the direction of incidence. A typical example of such a diode can be created by combining two mirrorsymmetric microcavities where modes of the opposite parity dominate. It is shown that a strong nonreciprocal behavior can be achieved together with a negligible insertion loss. To describe the dynamical properties of such systems, a model based on the coupledmode theory is developed, and a possible implementation in the form of multilayered structures is considered. (C) 2011 Optical Society of America
Phase noise suppression in a DPSK transmission system by the use of an
attenuationimbalanced NOLM
C. Stephan, K. Sponsel, G. Onishchukov, B. Schmauss, G. Leuchs
A nonlinear optical loop mirror (NOLM) imbalanced by attenuation has been used for the suppression of nonlinear phase noise in a DPSK transmission system. It has been experimentally shown that such a passive, NOLMbased regenerator can significantly improve the performance of a phaseencoded transmission when it is limited by nonlinear phase noise. A brief overview over the advantages und limitations of different NOLMbased phasepreserving amplitude regenerators is also given. (C) 2011 Elsevier B.V. All rights reserved.
Nonlinear wavelength conversion in photonic crystal fibers with three
zerodispersion points
S. P. Stark, F. Biancalana, A. Podlipensky, P. St. J. Russell
In this theoretical study, we show that a simple endlessly singlemode photonic crystal fiber can be designed to yield, not just two, but three zerodispersion wavelengths. The presence of a third dispersion zero creates a rich phasematching topology, enabling enhanced control over the spectral locations of the fourwavemixing and resonantradiation bands emitted by solitons and short pulses. The greatly enhanced flexibility in the positioning of these bands has applications in wavelength conversion, supercontinuum generation, and pairphoton sources for quantum optics.
Growth of axial SiGe heterostructures in nanowires using pulsed laser
deposition
Bjoern Eisenhawer, Vladimir Sivakov, Andreas Berger, Silke Christiansen
Axial heterojunctions between pure silicon and pure germanium in nanowires have been realized combining pulsed laser deposition, chemical vapor deposition and electron beam evaporation in a vaporliquidsolid nanowire growth experiment using gold nanoparticles as catalyst for the 1D wire growth. Energy dispersive xray mappings and line scans show a compositional transition from pure silicon to pure germanium and vice versa with exponential and thus comparably sharp transition slopes. Based on these results not only SiGe heterojunctions seem to be possible using the vaporliquidsolid growth process but also heterojunctions in optoelectronic IIIV compounds such as InGaAs/GaAs or group III nitride compounds such as InGaN/GaN as well as axial pn junctions in Si nanowires.
Device Calibration Impacts Security of Quantum Key Distribution
Nitin Jain, Christoffer Wittmann, Lars Lydersen, Carlos Wiechers, Dominique Elser, Christoph Marquardt, Vadim Makarov, Gerd Leuchs
Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Moreover, an inappropriately implemented calibration routine can open a fatal security loophole. We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial QKD system by deceiving a channel length calibration routine. We then devise an optimal and realistic strategy using faked states to break the security of the cryptosystem. A fix for this loophole is also suggested.
Silicon nanowires have been introduced into P3HT:[60]PCBM solar cells, resulting in hybrid organic/inorganic solar cells. A cell efficiency of 4.2% has been achieved, which is a relative improvement of 10% compared to a reference cell produced without nanowires. This increase in cell performance is possibly due to an enhancement of the electron transport properties imposed by the silicon nanowires.
In this paper, we present a novel approach for introducing the nanowires by mixing them into the polymer blend and subsequently coating the polymer/nanowire blend onto a substrate. This new onset may represent a viable pathway to producing nanowireenhanced polymer solar cells in a reel to reel process.
Entangling Different Degrees of Freedom by Quadrature Squeezing
Cylindrically Polarized Modes
C. Gabriel, A. Aiello, W. Zhong, T. G. Euser, N. Y. Joly, P. Banzer, M. Foertsch, D. Elser, U. L. Andersen, Ch. Marquardt, et al.
Quantum systems such as, for example, photons, atoms, or BoseEinstein condensates, prepared in complex states where entanglement between distinct degrees of freedom is present, may display several intriguing features. In this Letter we introduce the concept of such complex quantum states for intense beams of light by exploiting the properties of cylindrically polarized modes. We show that already in a classical picture the spatial and polarization field variables of these modes cannot be factorized. Theoretically it is proven that by quadrature squeezing cylindrically polarized modes one generates entanglement between these two different degrees of freedom. Experimentally we demonstrate amplitude squeezing of an azimuthally polarized mode by exploiting the nonlinear Kerr effect in a specially tailored photonic crystal fiber. These results display that such novel continuousvariable entangled systems can, in principle, be realized.
Fiber Transport of Spatially Entangled Photons
W. Loeffler, T. G. Euser, E. R. Eliel, M. Scharrer, P. St J. Russell, J. P. Woerdman
Entanglement in the spatial degrees of freedom of photons is an interesting resource for quantum information. For practical distribution of such entangled photons, it is desirable to use an optical fiber, which in this case has to support multiple transverse modes. Here we report the use of a hollowcore photonic crystal fiber to transport spatially entangled qubits.
Reconfigurable lightdriven optoacoustic isolators in photonic crystal
fibre
Dynamic optical isolation with alloptical switching capability is in great demand in advanced optical communications and alloptical signal processing systems. Most conventional optical isolators rely on Faraday rotation and are realized using micro/nanofabrication techniques, but it is not always straightforward to incorporate magnetooptical crystals into these compact systems. Here, we report the experimental demonstration of a reconfigurable alloptical isolator based on optical excitation of a gigahertz guided acoustic mode in a micrometresized photonic crystal fibre core. This device has remarkable advantages over its passive counterparts, including a large dynamic range of isolation, fast switching capability and reversibility, which provide new functionality that is useful in various types of alloptical systems. Devices based on similar physical principles could also be realized in CMOScompatible silicon onchip platforms.
Lasing in localized modes of a slow light photonic crystal waveguide
JinKyu Yang, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Frank Vollmer, Hui Cao
We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum dots as gain medium. Structural disorder is present due to fabrication imperfection and causes multiple scattering of light and localization of light. Lasing modes with varying spatial extend are observed at random locations along the guide. Lasing frequencies are determined by the local structure and occur within a narrow frequency band which coincides with the slow light regime of the waveguide mode. The threedimensional numerical simulation reveals that the main loss channel for lasing modes located away from the waveguide end is outofplane scattering by structural disorder. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600344]
Quick root searching method for resonances of dielectric optical
microcavities with the boundary element method
ChangLing Zou, Harald G. L. Schwefel, FangWen Sun, ZhengFu Han, GuangCan Guo
In this paper, we developed an efficient method for searching the resonant eigenfrequency of dielectric optical microcavities by the boundary element method. By transforming the boundary integral equation to a general eigenvalue problem for arbitrary, symmetric, and multidomain shaped optical microcavities, we analyzed the regular motion of the eigenvalues against the frequency. The new strategy can predict multiple resonances, increase the speed of convergence, and avoid nonphysical spurious solutions. These advantages greatly reduce the computation time in the search process of the resonances. Moreover, this method is not only valuable for dielectric microcavities, but is also suitable for other photonic systems with dissipations, whose resonant eigenfrequencies are complex numbers. (C) 2011 Optical Society of America
Quantum Light from a WhisperingGalleryMode Disk Resonator
J. U. Fuerst, D. V. Strekalov, D. Elser, A. Aiello, U. L. Andersen, Ch Marquardt, G. Leuchs
Optical parametric downconversion has proven to be a valuable source of nonclassical light. The process is inherently able to produce twinbeam correlations along with individual intensity squeezing of either parametric beam, when pumped far above threshold. Here, we present for the first time the direct observation of intensity squeezing of 1.2 dB of each of the individual parametric beams in parametric downconversion by use of a high quality whisperinggallerymode disk resonator. In addition, we observed twinbeam quantum correlations of 2.7 dB with this cavity. Such resonators feature strong optical confinement and offer tunable coupling to an external optical field. This work exemplifies the potential of crystalline whisperinggallerymode resonators for the generation of quantum light. The simplicity of this device makes the application of quantum light in various fields highly feasible.
Absolute calibration of photodetectors: photocurrent multiplication
versus photocurrent subtraction
I. N. Agafonov, M. V. Chekhova, T. S. Iskhakov, A. N. Penin, G. O. Rytikov, O. A. Shcherbina
OPTICS LETTERS
36(8)
13291331
(2011)
We report testing of the new absolute method of photodetector calibration based on the differencesignal measurement for twomode squeezed vacuum by comparison with the traditional absolute method based on coincidence counting. Using lowgain parametric downconversion, we have measured the quantum efficiency of a counting detector by both methods. The differencesignal method was adapted for the counting detectors by taking into account the deadtime effect. (c) 2011 Optical Society of America
How to Decompose Arbitrary ContinuousVariable Quantum Operations
We present a general, systematic, and efficient method for decomposing any given exponential operator of bosonic mode operators, describing an arbitrary multimode Hamiltonian evolution, into a set of universal unitary gates. Although our approach is mainly oriented towards continuousvariable quantum computation, it may be used more generally whenever quantum states are to be transformed deterministically, e. g., in quantum control, discretevariable quantum computation, or Hamiltonian simulation. We illustrate our scheme by presenting decompositions for various nonlinear Hamiltonians including quartic Kerr interactions. Finally, we conclude with two potential experiments utilizing offlineprepared optical cubic states and homodyne detections, in which quantum information is processed optically or in an atomic memory using quadratic lightatom interactions.
Accessing photon bunching with a photon number resolving multipixel
detector
Dmitry A. Kalashnikov, Si Hui Tan, Maria V. Chekhova, Leonid A. Krivitsky
In quantum optics and its applications, there is an urgent demand for photonnumber resolving detectors. Recently, there appeared multipixel counters (MPPC) that are able to distinguish between 1,2,..10 photons. At the same time, strong coupling between different pixels (crosstalk) hinders their photonnumber resolution. In this work, we suggest a method for 'filtering out' the crosstalk effect in the measurement of intensity correlation functions. The developed approach can be expanded to the analysis of higherorder intensity correlations by using just a single MPPC. (C) 2011 Optical Society of America
Polarization properties of macroscopic Bell states
Timur Sh. Iskhakov, Ivan N. Agafonov, Maria V. Chekhova, Georgy O. Rytikov, Gerd Leuchs
The four twophoton polarization Bell states are one of the main instruments in the toolbox of quantum optics and quantum information. In our experiment we produce their multiphoton counterparts, macroscopic Bell states. These are relevant to applications in quantum technologies because they provide efficient interactions with material quantum objects and with each other via nonlinear interactions. Furthermore, we study the polarization properties of these states using the concept of secondorder degree of polarization and its higherorder generalization.
Local Gaussian operations can enhance continuousvariable entanglement
distillation
Entanglement distillation is a fundamental building block in longdistance quantum communication. Though known to be useless on their own for distilling Gaussian entangled states, local Gaussian operations may still help to improve nonGaussian entanglement distillation schemes. Here we show that by applying local squeezing operations both the performance and the efficiency of existing distillation protocols can be enhanced. We find that such an enhancement through local Gaussian unitaries can be obtained even when the initially shared Gaussian entangled states are mixed, as, for instance, after their distribution through a lossyfiber communication channel.
A quantum pulse gate based on spectrally engineered sum frequency
generation
Andreas Eckstein, Benjamin Brecht, Christine Silberhorn
We introduce the concept of a quantum pulse gate (QPG), a method for accessing the intrinsic broadband spectral mode structure of ultrafast quantum states of light. This mode structure can now be harnessed for applications in quantum information processing. We propose an implementation in a PPLN waveguide, based on spectrally engineered sum frequency generation (SFG). It allows us to pick welldefined spectral broadband modes from an ultrafast multimode state for interconversion to a broadband mode at another frequency. By pulseshaping the bright SFG pump beam, different orthogonal broadband modes can be addressed individually and extracted with high fidelity. (C) 2011 Optical Society of America
Asymptotic Analysis of Flow Processes at Drawing of Single Optical
Microfibres
Giovanni Luzi, Philipp Epple, Michael Scharrer, Ken Fujimoto, Cornelia Rauh, Antonio Delgado
INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING
9
A65
(2011)
Microstructured optical fibres (i.e. fibres that contain holes) have assumed a high profile in recent years, and given rise to many novel optical devices. The problem of manufacturing such fibres by heating and then drawing a preform is considered for both the cases of annular microfibres and annular capillaries. A fluidmechanics model suggested in literature that uses asymptotic analysis based on the small aspect ratio of capillaries is analysed and revised. The leadingorder equations are examined in some asymptotic limits, many of which give valuable practical information about the control parameters that influence the drawing process. Additionally, the solution obtained for a single capillary provides a suitable basis for describing more complicated fibre structures.
Intensity correlations of thermal light
T. Iskhakov, A. Allevi, D. A. Kalashnikov, V. G. Sala, M. Takeuchi, M. Bondani, M. Chekhova
EUROPEAN PHYSICAL JOURNALSPECIAL TOPICS
199(1)
127138
(2011)

Journal
We demonstrate measurement of normalized Glauber's intensity correlation functions of different orders using an array photodetector. As the light source, we use a laser beam scattered by a rotating groundglass disc, which has statistics close to that of thermal light. We compare the measurements of the normalized correlation functions to that of the differenceintensity variance and show that they are in a certain sense complementary. The independence of the variance measurement on the number of temporal modes has been demonstrated for the first time. Different versions of highorder ghost imaging are also realized and characterized quantitatively.
Complex Faraday Rotation in Microstructured Magnetooptical Fiber
Waveguides
Markus A. Schmidt, Lothar Wondraczek, Ho W. Lee, Nicolai Granzow, Ning Da, Philip St. J. Russell
Magnetooptical glasses are of considerable current interest, primarily for applications in fiber circuitry, optical isolation, alloptical diodes, optical switching and modulation. While the benchmark materials are still crystalline, glasses offer a variety of unique advantages, such as very high rareearth and heavymetal solubility and, in principle, the possibility of being produced in fiber form. In comparison to conventional fiberdrawing processes, pressureassisted meltfilling of microcapillaries or photonic crystal fibers with magnetooptical glasses offers an alternative route to creating complex waveguide architectures from unusual combinations of glasses. For instance, strongly diamagnetic tellurite or chalcogenide glasses with high refractive index can be combined with silica in an allsolid, microstructured waveguide. This promises the implementation of asyetunsuitable but strongly active glass candidates as fiber waveguides, for example in photonic crystal fibers.
GoosHanchen and ImbertFedorov shifts of a nondiffracting Bessel beam
GoosHanchen (GH) and ImbertFedorov (IF) shifts are diffractive corrections to geometric optics that have been extensively studied for a Gaussian beam that is reflected or transmitted by a dielectric interface. Propagating in free space before and after reflection or transmission, such a Gaussian beam spreads due to diffraction. We address here the question of how the GH and IF shifts behave for a "nondiffracting" Bessel beam. (C) 2011 Optical Society of America
Aftergate attack on a quantum cryptosystem
C. Wiechers, L. Lydersen, C. Wittmann, D. Elser, J. Skaar, Ch Marquardt, V. Makarov, G. Leuchs
We present a method to control the detection events in quantum key distribution systems that use gated singlephoton detectors. We employ bright pulses as faked states, timed to arrive at the avalanche photodiodes outside the activation time. The attack can remain unnoticed, since the faked states do not increase the error rate per se. This allows for an interceptresend attack, where an eavesdropper transfers her detection events to the legitimate receiver without causing any errors. As a side effect, afterpulses, originating from accumulated charge carriers in the detectors, increase the error rate. We have experimentally tested detectors of the system id3110 (Clavis2) from ID Quantique. We identify the parameter regime in which the attack is feasible despite the side effect. Furthermore, we outline how simple modifications in the implementation can make the device immune to this attack.
An azimuthally polarizing photonic crystal fibre with a central gold
nanowire
Patrick Uebel, Markus A. Schmidt, Michael Scharrer, Philip St J. Russell
An airsilica photonic crystal fibre with a gold nanowire at core centre is shown to support a lowloss azimuthally polarized mode. Since all the other modes have very high attenuation, the fibre effectively supports only this mode, acting as a singlepolarization fibre with an extinction ratio >20 dB cm(1) over a broad range of wavelengths (5501650 nm in the device reported). It can be used as an effective azimuthal mode filter.
Singlemode hollowcore photonic crystal fiber made from soft glass
X. Jiang, T. G. Euser, A. Abdolvand, F. Babic, F. Tani, N. Y. Joly, J. C. Travers, P. St J. Russell
We demonstrate the first softglass hollow core photonic crystal fiber. The fiber is made from a highindex leadsilicate glass (Schott SF6, refractive index 1.82 at 500 nm). Fabricated by the stackanddraw technique, the fiber incorporates a 7cell hollow core embedded in a highly uniform 6layer cladding structure that resembles a kagomelike lattice. Effective single mode guidance of light is observed from 750 to 1050 nm in a large mode area (core diameter similar to 30 mu m) with a low loss of 0.74 dB/m. The underlying guidance mechanism of the fiber is investigated using finite element modeling. The fiber is promising for applications requiring single mode guidance in a large mode area, such as particle guidance, fluid and gas filled devices. (C) 2011 Optical Society of America
COMPARATIVE TEST OF TWO METHODS OF QUANTUM EFFICIENCY ABSOLUTE
MEASUREMENT BASED ON SQUEEZED VACUUM DIRECT DETECTION
I. N. Agafonov, M. V. Chekhova, A. N. Penin, G. O. Rytikov, O. A. Shumilkina, T. Sh Iskhakov
INTERNATIONAL JOURNAL OF QUANTUM INFORMATION
9
251262
(2011)

Journal
We realize and test in experiment a method recently proposed for measuring absolute quantum efficiency of analog photodetectors. Similar to the traditional (Klyshko) method of absolute calibration, the new one is based on the direct detection of twomode squeezed vacuum at the output of a traveling wave OPA. However, in the new method, one measures the differencephotocurrent variance rather than the correlation function of photocurrents (number of coincidences), which makes the technique applicable for highgain OPA. In this work we test the new method versus the traditional one for the case of photoncounting detectors where both techniques are valid.
Photon Propagation in a Discrete Fiber Network: An Interplay of
Coherence and Losses
Alois Regensburger, Christoph Bersch, Benjamin Hinrichs, Georgy Onishchukov, Andreas Schreiber, Christine Silberhorn, Ulf Peschel
We study light propagation in a photonic system that shows stepwise evolution in a discretized environment. It resembles a discretetime version of photonic waveguide arrays or quantum walks. By introducing controlled photon losses to our experimental setup, we observe unexpected effects like subexponential energy decay and formation of complex fractal patterns. This demonstrates that the interplay of linear losses, discreteness and energy gradients leads to genuinely new coherent phenomena in classical and quantum optical experiments. Moreover, the influence of decoherence is investigated.
Multilevel PhasePreserving Amplitude Regeneration Using a Single
Nonlinear Amplifying Loop Mirror
Martin Hierold, Tobias Roethlingshoefer, Klaus Sponsel, Georgy Onishchukov, Bernhard Schmauss, Gerd Leuchs
A possibility of multilevel phasepreserving amplitude regeneration using a nonlinear amplifying loop mirror (NALM) is presented for the optical star8 quadrature amplitude modulation (QAM) transmission format as an example. Two significantly different state power ratios for the QAM signal, 1:3 and 1:7, were investigated. After the optimization of the coupler splitting ratio and the directional phase bias in the NALM, amplitude noise can be efficiently suppressed at both signal power levels simultaneously. Biterrorratio (BER) simulations have shown that in a system limited by nonlinear phase noise, the deployment of the NALM allows an increase of the fiber launch power by 1.9 and 2.2 dB at a BER of 10(3) for a state power ratio of 1:3 and 1:7, respectively. The regeneration limits due to imperfections of the power transfer characteristic are also discussed.
Classical and quantum properties of cylindrically polarized states of
light
Annemarie Holleczek, Andrea Aiello, Christian Gabriel, Christoph Marquardt, Gerd Leuchs
We investigate theoretical properties of beams of light with nonuniform polarization patterns. Specifically, we determine all possible configurations of cylindrically polarized modes (CPMs) of the electromagnetic field, calculate their total angular momentum and highlight the subtleties of their structure. Furthermore, a hybrid spatiopolarization description for such modes is introduced and developed. In particular, two independent Poincare spheres have been introduced to represent simultaneously the polarization and spatial degree of freedom of CPMs. Possible modetomode transformations accomplishable with the help of Bconventional polarization and spatial phase retarders are shown within this representation. Moreover, the importance of these CPMs in the quantum optics domain due to their classical features is highlighted. (C) 2011 Optical Society of America
Enhanced Sensing of Nonpolar Volatile Organic Compounds by Silicon
Nanowire Field Effect Transistors
Yair Paska, Thomas Stelzner, Silke Christiansen, Hossam Haick
Silicon nanowire field effect transistors (Si NW FETs) are emerging as powerful sensors for direct detection of biological and chemical species. However, the low sensitivity of the Si NW FET sensors toward nonpolar volatile organic compounds (VOCs) Is problematic for many applications. In this study, we show that modifying Si NW FETs with a silane monolayer having a low fraction of S1OSi bonds between the adjacent molecules greatly enhances the sensitivity toward nonpoiar VOCs. This can be explained in terms of an indirect sensor VOC interaction, whereby the nonpolar VOC molecules induce conformational changes in the organic monoiayer, affecting (i) the dielectric constant and/or effective dipole moment of the organic monolayer and/or (ii) the density of charged surface states at the SiO(2)/monolayer interface. In contrast, polar VOCs are sensed directly via VOCinduced changes in the Si NW charge carriers, most probably due to electrostatic interaction between the Si NW and polar VOCs. A semiempirical model for the VOCinduced conductivity changes in the Si NW FETs is presented and discussed.
Artificial boundary conditions for certain evolution PDEs with cubic
nonlinearity for noncompactly supported initial data
V. Vaibhav
JOURNAL OF COMPUTATIONAL PHYSICS
230(8)
32053229
(2011)

Journal
The paper addresses the problem of constructing nonreflecting boundary conditions for two types of one dimensional evolution equations, namely, the cubic nonlinear Schrodinger (NLS) equation, partial derivative(t)u + Lu  i chi vertical bar u vertical bar(2)u = 0 with L i partial derivative(2)(x), and the equation obtained by letting L partial derivative(3)(x). The usual restriction of compact support of the initial data is relaxed by allowing it to have a constant amplitude along with a linear phase variation outside a compact domain. We adapt the pseudodifferential approach developed by Antoine et al. (2006) [5] for the NLS equation to the second type of evolution equation, and further, extend the scheme to the aforementioned class of initial data for both of the equations. In addition, we discuss efficient numerical implementation of our scheme and produce the results of several numerical experiments demonstrating its effectiveness. (C) 2011 Elsevier Inc. All rights reserved.
Nanoparticlebased protein detection by optical shift of a resonant
microcavity
Miguel A. SantiagoCordoba, Svetlana V. Boriskina, Frank Vollmer, Melik C. Demirel
We demonstrated a biosensing approach which, for the first time, combines the high sensitivity of whispering gallery modes (WGMs) with a metallic nanoparticlebased assay. We provided a computational model based on generalized Mie theory to explain the higher sensitivity of protein detection. We quantitatively analyzed the binding of a model protein (i.e., Bovine Serum Albumin) to gold nanoparticles from highQ WGM resonance frequency shifts, and fit the results to an adsorption isotherm, which agrees with the theoretical predictions of a twocomponent adsorption model. (C) 2011 American Institute of Physics. [doi:10.1063/1.3599706]
The Direct Writing of Plasmonic Gold Nanostructures by
ElectronBeamInduced Deposition
Katja Hoeflich, Ren Bin Yang, Andreas Berger, Gerd Leuchs, Silke Christiansen
Various nanostructures are directly written by electronbeaminduced deposition using dimethylgold(III)acetylacetonate as the precursor gas. After purification, their potential applications include plasmonic devices and metamaterials. Carbon contamination of the aswritten structures can be completely removed by lowtemperature ozone treatment, leaving polycrystalline pure gold structures (see figure). This treatment reduces the size of the nanostructures but does not substantially alter their functional shape.
Theory of anisotropic whisperinggallerymode resonators
An analytic solution for a uniaxial spherical resonator is presented using the method of Debye potentials. This serves as a starting point for the calculation of whispering gallery modes (WGMs) in such a resonator. Suitable approximations for the radial functions are discussed in order to best characterize WGMs. The characteristic equation and its asymptotic expansion for the anisotropic case is also discussed, and an analytic formula with a precision of the order O[nu(1)] is also given. Our careful treatment of both boundary conditions and asymptotic expansions makes the present work a particularly suitable platform for a quantum theory of whispering gallery resonators.
Multiwalker discrete time quantum walks on arbitrary graphs, their
properties and their photonic implementation
Peter P. Rohde, Andreas Schreiber, Martin Stefanak, Igor Jex, Christine Silberhorn
Quantum walks have emerged as an interesting alternative to the usual circuit model for quantum computing. While still universal for quantum computing, the quantum walk model has very different physical requirements, which lends itself more naturally to some physical implementations, such as linear optics. Numerous authors have considered walks with one or two walkers, on onedimensional graphs, and several experimental demonstrations have been performed. In this paper, we discuss generalizing the model of discrete time quantum walks to the case of an arbitrary number of walkers acting on arbitrary graph structures. We present a formalism that allows for the analysis of such situations, and several example scenarios for how our techniques can be applied. We consider the most important features of quantum walksmeasurement, distinguishability, characterization and the distinction between classical and quantum interference. We also discuss the potential for physical implementation in the context of linear optics, which is of relevance to presentday experiments.
Perfect imaging of hypersurfaces via transformation optics
Conventional optical imaging systems suffer from the presence of many imperfections, such as spherical aberrations, astigmatism, or coma. If the imaging system is corrected for spherical aberrations and fulfills the Abbe sine condition, perfect imaging is guaranteed between two parallel planes but only in a small neighborhood of the optical axis. It is therefore worth asking for optical systems that would allow for perfect imaging between arbitrary smooth surfaces without restrictions in shape or extension. In this Letter, we describe the application of transformation optics to design refractive index distributions that allow perfect, aberrationfree imaging for various imaging configurations in R(n). A special case is the imaging between two extended parallel lines in R(2), which leads to the wellknown hyperbolic secant index distribution that is used for the fabrication of gradient index lenses. (C) 2011 Optical Society of America
Coupledmode theory for onchannel nonlinear microcavities
Victor Grigoriev, Fabio Biancalana
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA BOPTICAL PHYSICS
28(9)
21652173
(2011)
We consider a nonlinear microcavity separating a waveguide channel into two parts so that the coupling between them is possible only due to the resonant properties of the microcavity. We provide a rigorous derivation of the equations used in the phenomenological coupledmode theory for such systems. This allows us to find the explicit formulas for all fitting parameters such as decay rates, coupling coefficients, and characteristic intensities in terms of the mode profiles. The advantages of using the semianalytical approach are discussed, and the accuracy of the results is compared with strictly numerical methods. Particular attention is paid to multilayered structures since they represent the simplest realization of onchannel microcavities. (C) 2011 Optical Society of America
This Letter reports an experimental and theoretical study of the response of a quadrant detector (QD) to an incident vortex beam, specifically a LaguerreGaussian (LG) beam. We have found that the LG beam response depends on the vorticity index l. We compare LG beams with hardringed beams and find that at higher l values, the QD response to LG beams can be approximated by its response to hardringed beams. Our findings are important in view of the increasing interest in optical vortex beams. (C) 2011 Optical Society of America
Realistic g((2)) measurement of a PDC source with single photon
detectors in the presence of background
Andreas Eckstein, Andreas Christ, Peter J. Mosley, Christine Silberhorn
Physica Status Solidi CCurrent Topics in Solid State Physics
8(4)
(2011)

Journal
The g(2) correlation function of a light beam depends on its photon statistcs. In quantum optics, this effect can be used to determine the effective mode number of a type II parametric downconversion source. However, the outcome is very sensitive against background light from other sources. We consider the experimental challenges of this approach and introduce a simple model to account for influence of the background. (C) 2011 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim
Spectral overlap in direct measurements of displaced singlephoton
states
K. Laiho, M. Avenhaus, K. N. Cassemiro, C. Silberhorn
Many sophisticated quantum states of light display nonclassical, characteristic oscillations in their photon statistics altering with respect to the applied displacement. In order to detect these oscillations the mode matching between the studied state and the displacement field plays a crucial role. Only recently the developments in the photon counting techniques have allowed the direct measurements of the photonnumber distributions of quantum states. We investigate the properties of displaced single photons by applying timemultiplexed detection of photon statistics and quantify the value of the mode overlap.
Recent Developments in Hybrid Photonic Crystal Fiber
M. A. Schmidt, H. Lee, H. Tyagi, P. Uebel, N. Granzow, P. St J. Russell
2011 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS
(ICTON)
(2011)
We review our results of hybrid photonic crystal fibers. We explain the important properties of spiralling plasmons on wires and in arrays and discuss our main experimental achievements such as excitation of superplasmon modes. Moreover, we'll discuss our developments sophisticated polarization devices.
Highperformance singlephoton generation with commercialgrade optical
fiber
Christoph Soeller, Offir Cohen, Brian J. Smith, Ian A. Walmsley, Christine Silberhorn
Highquality quantum sources are of paramount importance for the implementation of quantum technologies. We present here a heralded singlephoton source based on commercialgrade polarizationmaintaining optical fiber. The heralded photons exhibit a purity of at least 0.84 and an unprecedented heralding efficiency into a singlemode fiber of 85%. The birefringent phasematching condition of the underlying fourwave mixing process can be controlled mechanically to optimize the wavelength tuning needed for interfacing multiple sources, as is required for largescale entanglement generation.
Soliton Blueshift in Tapered Photonic Crystal Fibers
We show that solitons undergo a strong blueshift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a smallcore photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zerodispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards a shorter wavelength. This is accompanied by strong emission of radiation into the UV and IR spectral regions. The experimental results are confirmed by numerical simulation.
Optofluidic immobility of particles trapped in liquidfilled hollowcore
photonic crystal fiber
We study the conditions under which a particle, laserguided in a verticallyoriented hollowcore photonic crystal fiber filled with liquid, can be kept stationary against a microfluidic counterflow. An immobility parameterthe fluid flow rate required to immobilize a particle against the radiation force produced by unit guided optical poweris introduced to quantify the conditions under which this occurs, including radiation, viscous and gravity forces. Measurements show that this parameter depends strongly on the ratio of particle radius a to core radius R, peaking at an intermediate value of a/R. The results follow fairly well the theoretical estimates of the optical (calculated approximately using a ray optics approach) and numerically simulated drag forces. We suggest that the system has potential applications in, e.g., measurement of the diameter, refractive index and density of particles, synthesis and biomedical research. (C) 2011 Optical Society of America
Bright Spatially Coherent WavelengthTunable DeepUV Laser Source Using
an ArFilled Photonic Crystal Fiber
N.Y. Joly, J. Nold, W. Chang, P. Hoelzer, A. Nazarkin, G. K. L. Wong, F. Biancalana, P. St. J. Russell
We report on the spectral broadening of similar to 1 mu J 30 fs pulses propagating in an Arfilled hollowcore photonic crystal fiber. In contrast with supercontinuum generation in a solidcore photonic crystal fiber, the absence of Raman and unique pressurecontrolled dispersion results in efficient emission of dispersive waves in the deepUV region. The UV light emerges in the singlelobed fundamental mode and is tunable from 200 to 320 nm by varying the pulse energy and gas pressure. The setup is extremely simple, involving <1 m of a gasfilled photonic crystal fiber, and the UV signal is stable and bright, with experimental IR to deepUV conversion efficiencies as high as 8 %. The source is of immediate interest in applications demanding high spatial coherence, such as laser lithography or confocal microscopy.
Structural analysis of photonic crystal fibers by side scattering of
laser light
L. Y. Zang, T. G. Euser, M. S. Kang, M. Scharrer, P. St. J. Russell
OPTICS LETTERS
36(9)
16681670
(2011)
A sidescattering technique for investigating the inner microstructure of photonic crystal fibers (PCFs) is reported. Multiple scattering is reduced by filling the hollow PCF channels with indexmatching fluid. The scattered signal is measured for fixed angles of incidence and detection while the fiber is rotated. A pattern of peaks, unique to each PCF, whether solid or hollow core, correlates closely with the symmetry planes of the PCF structure. As an example of the technique, the twist profile of a structural rocking filter is directly measured. (C) 2011 Optical Society of America
Statistical model on the optical properties of silicon nanowire mats
Gerald Broenstrup, Frank Garwe, Andrea Csaki, Wolfgang Fritzsche, Andrea Steinbrueck, Silke Christiansen
Randomly grown silicon nanowire (SiNW) mats show a high light absorption even for long wavelengths despite the small volume of silicon. We present a statistical model that gives a physical understanding of the mechanisms of the absorption and scattering of light in such SiNW mats. According to this model the two main mechanisms of the effective absorption of light are (i) resonant optical antenna effects of the absorption within the individual SiNWs and (ii) the interaction of the light with several SiNWs in the mat due to strong light scattering. The results of this model are in good agreement with the experimental reflection, transmission, and absorption spectra taken with an integrating sphere.
From Plasmonics to Supercontinuum Generation: Subwavelength Scale
Devices Based on Hybrid Photonic Crystal Fibers
M. A. Schmidt, H. Tyagi, H. Lee, N. Granzow, N. Da, M. Peng, L. Wondraczek, P. St. J. Russell
International Conference on Transparent Optical NetworksICTON
(2011)
Photonic crystal fibers (PCFs) consist of arrays of micrometersize hollow channels extending along the entire fiber length. A new approach to modify the optical properties and to improve the design flexibility of such fibers is to fill the air holes of the array by with different materials, realizing allsolid hybrid fiber structures. In this talk, recent results on silica PCF filled with noble metals, semiconductors or soft glasses are presented. Depending on the actual material being filled into the holes, we observed plasmonic excitations, Mieresonances and photonic band gaps.
A method for performing high accuracy temperature measurements in
lowpressure sooting flames using twoline atomic fluorescence
Iain S. Burns, Xavier Mercier, Maxime Wartel, Robin S. M. Chrystie, Johan Hult, Clemens F. Kaminski
PROCEEDINGS OF THE COMBUSTION INSTITUTE
33
799806
(2011)

Journal
We demonstrate a step change in the capability of diode laser excited twoline atomic fluorescence (TLAF) thermometry and show it is wellsuited to the study of lowpressure sooting flames. The new developments to the technique reported here were essential to achieve the accuracy (+/41 K) and precision (+/8 K) required for useful measurements in such systems. This represents the first application of TLAF thermometry to the investigation of lowpressure sooting flames, an environment in which other thermometry techniques perform poorly. We thus demonstrate a practical application of diode laser TLAF to a burner that is the subject of a coordinated experimental and computational investigation of soot formation. The TLAF technique requires no calibration measurement and is compact and economical to set up in comparison with traditional laser thermometry methods. Temperature profiles were recorded in a laminar flatflame operating on O2, N2 and CH4 at fuel equivalence ratio of 2.32 and pressures ranging from 18.7 to 26.7 kPa. Almost identical temperature profiles were observed at different pressures despite the fact that soot volume fractions changed by more than an order of magnitude between the lowest and highest operating pressures. The data will contribute to modelling efforts to understand the surprisingly strong dependence of soot volume fraction on pressure that has previously been observed under the range of conditions studied here and will be included in an openly available database on this flame, which includes species profile measurements obtained by other methods. In the current contribution we emphasise the technical implementation of diode TLAF as a new temperature diagnostic with near optimal characteristics for the study of low pressure, sooting flames. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
In this contribution, we propose linear optical realizations of arbitrary stabilizer quantum error correction (QEC) codes in any dimension, including discrete and continuous quantum variables. Our protocols use graph states to encode arbitrary logical states in a systematic way. In this fashion, the hardest part of the encoding procedure (i.e., the generation of multiparty correlations robust against local errors) is shifted offline into the preparation of the graphstate ancilla.
Frustrated quantum phase diffusion and increased coherence of solitons
due to nonlocality
We investigate the quantum properties of solitons with nonlocal selfinteraction. We find significant changes when compared to the local interaction. Quantum phase diffusion of nonlocal solitons is always reduced with respect to the local interaction and vanishes in the strongly nonlocal limit. Thus, coherence is increased in the nonlocal case. Furthermore, we compare the intrinsic quantum wave packet spreading to the recently discussed classical GordonHaus effect for nonlocal solitons [V. Folli and C. Conti, Phys. Rev. Lett. 104, 193901 (2010)].
Experimental Comparison of AllOptical PhasePreserving Amplitude
Regeneration Techniques
Daniel Endres, Christian Stephan, Klaus Sponsel, Georgy Onishchukov, Bernhard Schmauss, Gerd Leuchs
International Conference on Transparent Optical NetworksICTON
(2011)
Performance of a nonlinear amplifying loop mirror and a fiber optical parametric amplifier in saturation used as phasepreserving amplitude limiters was investigated in a setup simulating a DPSK transmission system. The Qfactor improvement as well as the power penalty reduction have been compared under identical conditions. Both regenerators provide a similar Qfactor improvement, but the nonlinear amplifying loop mirror yields a better power penalty reduction.
Entanglement properties of optical coherent states under amplitude
damping
Ricardo Wickert, Nadja Kolb Bernardes, Peter van Loock
Through concurrence, we characterize the entanglement of optical coherentstate qubits subject to an amplitude damping channel. We investigate the distillation capabilities of known error correcting codes and obtain upper bounds on the entanglement depending on the nonorthogonality of the input states and the channel damping parameter, thus quantitatively analysing these photonloss codes which are naturally reminiscent of the standard qubit codes against Pauli errors.
Concentrating the phase of a coherent state by means of probabilistic
amplification
Mario A. Usuga, Christian R. Mueller, Christoffer Wittmann, Petr Marek, Radim Filip, Christoph Marquardt, Gerd Leuchs, Ulrik L. Andersen
We discuss the recent implementation of phase concentration of an optical coherent state by use of a probabilistic noiseless amplifier. The operation of the amplifier is described pictorially with phase space diagrams, and the experimental results are outlined.
A planar dielectric antenna for directional singlephoton emission and
nearunity collection efficiency
K. G. Lee, X. W. Chen, H. Eghlidi, P. Kukura, R. Lettow, A. Renn, Vahid Sandoghdar, Stephan Götzinger
Single emitters have been considered as sources of single photons in various contexts, including cryptography, quantum computation, spectroscopy and metrology(13). The success of these applications will crucially rely on the efficient directional emission of photons into welldefined modes. To accomplish high efficiency, researchers have investigated microcavities at cryogenic temperatures(4,5), photonic nanowires(6,7) and nearfield coupling to metallic nanoantennas(810). However, despite impressive progress, the existing realizations substantially fall short of unity collection efficiency. Here, we report on a theoretical and experimental study of a dielectric planar antenna, which uses a layered structure to tailor the angular emission of a single oriented molecule. We demonstrate a collection efficiency of 96% using a microscope objective at room temperature and obtain record detection rates of similar to 50 MHz. Our scheme is wavelengthinsensitive and can be readily extended to other solidstate emitters such as colour centres(11,12) and semiconductor quantum dots(13,14).
Dynamics of coupled multimode and hybrid optomechanical systems
Georg Heinrich, Max Ludwig, Huaizhi Wu, K. Hammerer, Florian Marquardt
Recent experimental developments have brought into focus optomechanical systems containing multiple optical and mechanical modes interacting with each other. Examples include a setup with a movable membrane between two endmirrors and "optomechanical crystal" devices that support localized optical and mechanical modes in a photonic crystal type structure. We discuss how mechanical driving of such structures results in coherent photon transfer between optical modes, and how the physics of LandauZenerStueckelberg oscillations arises in this context. Another area where multiple modes are involved are hybrid systems. There, we review the recent proposal of a single atom whose mechanical motion is coupled to a membrane via the light field. This is a special case of the general principle of cavitymediated mechanical coupling. Such a setup would allow the welldeveloped tools of atomic physics to be employed to access the quantum state of the 'macroscopic' mechanical mode of the membrane. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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