# past events

## Distinguished Lecturer Series

Juggling with photons and raising Schrödinger cats of light in a cavity

### Speaker:

Prof Serge Haroche (Ecole Normale Supérieure and Collège de France, Paris)

### Place:

MPL / large seminar room (*435)

### Abstract:

The founders of quantum theory assumed in “thought experiments” that they were manipulating isolated quantum systems obeying the counterintuitive laws which they had just discovered. Technological advances have recently turned these virtual experiments into real ones by making possible the actual control of isolated quantum particles. Many laboratories are realizing such experiments, in a research field at the frontier between physics and information science. Fundamentally, these studies explore the transition between the microscopic world ruled by quantum laws and our macroscopic environment which appears “classical”. Practically, physicists hope that these experiments will result in new technologies exploiting the strange quantum logic to compute, communicate or measure physical quantities better than what was previously conceivable. In Paris, we perform such experiments by juggling with photons trapped between superconducting mirrors. We count these photons in a non-destructive way and we prepare states of the quantum field reminiscent of the famous cat which Schrödinger imagined to be suspended between life and death. I will give a simple description of these studies, compare them to similar ones performed on other systems and guess about possible applications.

## MPL Distinguished Lecturer Series

Spin Hall Effect for Electrons and Photons

### Speaker:

Prof Henry van Driel (Department of Physics, University of Toronto, Canada)

### Place:

MPL / large seminar room (*435)

### Abstract:

Hall effects have provided important insights into the electronic properties of solids since 1879. In the spin Hall effect, a pure electrical current produces a pure transverse spin current while the inverse spin Hall effect describes the converse situation. I describe the generation and detection of both these spin Hall effects in GaAs using coherence control optical techniques. An analogous spin Hall effect for light is also demonstrated wherein a linearly polarized light beam incident on, e.g., GaAs is split transversely into its spin, that is, right and left circularly polarized, components. Both electron and photon spin Hall effects involve nanometer displacements of charges or photons but can nonetheless be resolved optically.

## IMPRS get-together

**Place:** MPL (large seminar room *429/435, 4th floor)

**Organisation:** Michael Schmidberger (MPL / Russell Division)

**Talk:** Temporal cavity solitons: ultraweak acoustic interactions, phase-modulation trapping, dispersive waves, and Kerr frequency combs

**Speaker:** Prof. Stéphane Coen (University of Auckland, New Zealand)

**Abstract:**

In this talk, I will present recent experimental results obtained with temporal cavity solitons in a passive fibre ring resonator. I will first introduce the concept and properties of temporal cavity solitons, which are persistent pulses of coherently-driven passive nonlinear resonators. I will then show how these pulses interact very weakly over extremely long ranges through transverse acoustic waves. In the most extreme case, we observe pairs of temporal cavity solitons shifting their relative position by only half an attosecond per round-trip of the 100 m-long resonator and it takes an effective propagation distance of the order of an astronomical unit for the interaction to fully develop. In the second part, I will show how a synchronous phase-modulation of the coherent-driving beam can overcome the acoustic interaction by trapping the temporal cavity solitons in potential wells. We will also demonstrate that manipulation of the trapping potential gives us the ability to manipulate individual cavity solitons in a train, leading to selective temporal shifting of solitons, forced merging of neighboring solitons, and selective erasure. Finally, I will briefly present measurements in which temporal cavity solitons in low dispersion cavities are shown to radiate dispersive waves and how this connects to the generation of frequency combs in microresonators.

## IMPRS get-together

**Place:** MPL (large seminar room *429/435, 4th floor)

**Organisation:** Federico Belli (MPL / Russell Division)

**Talk:** Optical shock waves in disordered thermal lensing

**Speaker:** Dr. Silvia Gentilini (Sapienza University, Rome, Italy)

**Abstract:**

Shock waves (SWs) are an ubiquitous phenomenon observable in different areas, ranging from water waves to gas dynamics and from plasma to supernova explosions. They also appear in non-linear optics, where can occur in systems described by universal models, such as the non-linear Schrödinger equation, when the hydrodynamical approximation holds true. In dispersion dominated systems, as are the optical systems, the shock phenomenon is regularized by the emergence of fast oscillations, the so called *undular bores*. Given the coherent nature of the *undular bores*, disorder is expected to strongly affect the occurrence of dispersive shock waves (DSWs). We present our experimental investigations on the occurrence of DSWs in disordered, non-linear media. The experimental set-up allowed the visualization of a propagating Gaussian laser beam in thermal defocusing media in presence of controllable amount of disorder. We show that, by increasing the strength of non-linearity, the shock formation is enhanced, while, on the other hand, random light scattering hampers and eventually inhibits the wave breaking phenomenon. We characterized the thermal non-linearity of the system and we quantified the effect of disorder by measuring the first shock-no shock phase diagram in terms of non-linearity strength and disorder degree.

## MPL Distinguished Lecturer Series

From Extreme Nonlinear Optics to Ultrafast Atomic Physics

### Speaker:

Prof Anne L'Huillier (Department of Physics, Lund University, Sweden)

### Place:

MPL / large seminar room (*435)

### Abstract:

The interaction of atoms with intense laser radiation leads to the generation of high-order harmonics of the laser field. In the time domain, this corresponds to a train of pulses in the extreme ultraviolet range and with attosecond duration. This presentation will introduce the physics of high-order harmonnic generation and attosecond pulses and describe recent developments including multicolor schemes or noncollinear geometries.

After the first decade where attosecond pulses were characterized, analyzed and used in –mostly– demonstration experiments, we begin to perform experiments where these pulses allow us to explore new physics. We will describe some of these applications, and in particular recent results concerning single and double photoioniza¬tion dynamics.

## MPL Distinguished Lecturer Series

### Speaker:

Prof Jérôme Faist (Quantum Optoelectronics Group, ETH Zurich, Switzerland)

### Place:

MPL / large seminar room (*435)

### Abstract:

The quantum cascade laser has demonstrated operation over an extremely wide wavelength range extending from the mid-infrared at 2.9?m to the Terahertz at 360?m. One very important feature of this device is its ability to provide gain over a very broad wavelength range. Recently, we have shown that such broadband devices, when operated in continuous wave, emit as a coherent optical comb1 in which the phase relation between the comb modes corresponds approximately to a FM modulated laser. These new comb lasers enables the fabrication of a dual comb spectrometer based on a quantum cascade laser that offers a broadband, all solid-state spectrometer with no moving parts and a ultrafast acquisition time. We discuss also the extension of these ideas to the THz.

1. A. Hugi, G. Villares, S. Blaser, H. C. Liu and J. Faist, Nature 492 (7428), 229-233 (2012).

## IMPRS get-together

**Place:** Physikalisches Institut (Erwin-Rommel-Str. 1)

**Organisation:** Thomas Gleixner (FAU / ECAP)

**Talk:** Chemically produced graphene

**Speaker:** Dr. Michael Enzelberger-Heim

## MPL Distinguished Lecturer Series

### Speaker:

Prof. Robert L. Byer (Applied Physics, Stanford University, USA)

### Place:

MPL / large seminar room (*435)

### Abstract:

The generation and control of light is critical for meeting important laser accelerator challenges of the 21st century. I review progress toward a laser-driven accelerator on-a-chip fabricated using modern lithographic tools. The laser accelerator is ideal for driving a dielectric-undulator FEL for table top MHz repetition rate attosecond X-ray lasers. Recent progress and issues that remain to be resolved are identified.

## IMPRS get-together

**Place:** MPL (Lecture room 435, Bldg 24, Günther-Scharowsky-Str.1)

**Organisation:** Angela Pérez (MPL & FAU / Leuchs Division)

**Talk:** Higher quantum dimensionality by exploiting the photonic orbital angular momentum

**Speaker:** Fabio Sciarrino (Dipartimento di Fisica dell’Università “La Sapienza”, Roma 00185, Italy)

**Abstract:**

In quantum information processing based on optical techniques, single photons offer a variety of degrees of freedom in which information can be encoded. By exploiting these resources, it is possible to implement high-dimensional quantum states, or qudits, which enable higher security in quantum cryptographic protocols, as well as implications in fundamental quantum mechanics theory. In the last few years, many improvements have been achieved for qudit states with d = 3 (qutrits) and d = 4 (ququarts). In this framework, the orbital angular momentum of photons, being de?ned in an in?nitely dimensional Hilbert space, offers a promising resource for high-dimensional optical quantum information protocols. Recently we introduced and tested experimentally a series of optical schemes for the coherent transfer of quantum information from the polarization to the orbital angular momentum (OAM) of single photons and vice versa [1,2,3]. All our schemes exploit a newly developed optical device, the so-called “q-plate”, a suitably patterned non-uniform birefringent plate, which enables the manipulation of the photon orbital angular momentum driven by the polarization degree of freedom. Our experiments prove that these schemes are reliable, efficient and have a high ?delity. First we will present the experimental generation and manipulation of a hybrid ququart encoded in the polarization and orbital angular momentum of a single photon [4,5,8].

Hence we will discuss potential applications for quantum communication. For two or more parties to execute even the simplest quantum transmission, they must establish, and maintain, a shared reference frame. This introduces a considerable overhead in communication resources, particularly if the parties are in motion or rotating relative to each other. We experimentally demonstrate how to circumvent this problem with the efficient transmission of quantum information encoded in rotationally invariant states of single photons obtained by combining together the polarization and OAM degrees of freedom [6]. By developing a complete toolbox for the efficient encoding and decoding of quantum information in such photonic qubits, we demonstrate the feasibility of alignment-free quantum key-distribution, and perform a proof-of-principle alignment-free entanglement distribution and violation of a Bell inequality [6]. Finally we will report the demonstration of NOON-like photonic states of m quanta of angular momentum up to m=100, in a setup that acts as a ‘photonic gear’, converting, for each photon, a mechanical rotation of an angle into an amplified rotation of the optical polarization by a factor m, corresponding to a ‘super-resolving’ Malus’ law [7]. We show that this effect leads to single-photon angular measurements with the same precision of polarization-only quantum strategies with m photons, but robust to photon losses. Moreover, we combine the gear effect with the quantum enhancement due to entanglement, thus exploiting the advantages of both approaches. The high ‘gear ratio’ m boosts the current state of the art of optical non-contact angular measurements by almost two orders of magnitude [7].

**References**

[1] E. Nagali, F. Sciarrino, F. De Martini, L. Marrucci, B. Piccirillo, E. Karimi, and E. Santamato, * Phys. Rev. Lett.* **103**, 013601 (2009).

[2] E. Nagali, L. Sansoni, F. Sciarrino, F. De Martini, L. Marrucci, B. Piccirillo, E. Karimi, E. Santamato, *Nature Photonics* **3**, 720 (2009).

[3] E. Nagali, and F. Sciarrino, *Optics Express ***18**, 18243 (2010).

[4] E. Nagali, L. Sansoni, L. Marrucci, E. Santamato, F. Sciarrino, *Phys. Rev. A* **81**, 052317 (2010).

[5] E. Nagali, D. Giovannini, L. Marrucci, S. Slussarenko, E. Santamato, and F. Sciarrino, *Phys. Rev. Lett.* **105**, 073602 (2010).

[6] V. D'Ambrosio, et al., *Nat. Commun.* **3**, 961 (2012).

[7] V. D'Ambrosio, et al.,* Nat. Commun.* in press (2013).

[8] V. D'Ambrosio, I. Herbauts, E. Amselem, E. Nagali, M. Bourennane, F. Sciarrino, A. Cabello, *Phys. Rev. X* **3**, 011012 (2013).

## Visions in Science - Shaping the Future

**Place:** MPI-CBG, Dresden

**More information:** **http://www.visions-in-science.org/**