Quantum Nanomechanics - from levitation to many-body spin-spin interactions

17.11.2017, 11:00

 

Dr. Jan Gieseler, Harvard University

Nitrogen vacancy (NV) centers are promising candidates for quantum computation, with
room temperature optical spin read-out and initialization, microwave manipulability, and
weak coupling to the environment resulting in long spin coherence times. The major
outstanding challenge involves engineering coherent interactions between the spin states of
spatially separated NV centers. To address this challenge, we are working towards the
experimental realization of mechanical spin transducers.

The spin transducer consists of a magnetic mechanical resonator in proximity of the NV
centers. Consequently, the magnetic field at the NV location depends on the resonator
motion. On the other hand, spin flips of the electronic spin of the NV center exert a force on
the resonator. Hence, the spin-resonator interaction can be used to mediate an effective
spin-spin interaction between two distant NV centers that are coupled to the same
mechanical mode. This principle is in close analogy to trapped ions that interact via a
common mechanical mode and which have already demonstrated high fidelity quantum
gates. To maximize the coherent spin-resonator coupling it is required to employ a low
mass, high quality mechanical resonator, NV centers with very long spin coherence times,
strong magnetic field gradients, and to combine them while preserving the excellent
properties of the individual components. To date, we have successfully fabricated doublyclamped
silicon nitride mechanical resonators and fabricated nano-magnets on top of them
while maintaining a high-quality factor (Q>105). In addition, the resonators are integrated
close to a bulk diamond sample to access bulk NV centers with long coherence times and to
maximize the spin resonator coupling. In a second approach, we start with a levitated micromagnet
and aim at using its degrees of freedom to couple to the NV-center spin. The
absence of any support structure gives a large magnetic moment to mass ratio, which is
favorable for large couplings, and can give rise to low mechanical damping.

In this talk, I report on our experimental progress towards achieving a coherent coupling of
the motion of these resonators with the electronic spin states of individual NV centers under
cryogenic conditions. Such a system is expected to provide a scalable platform for
mediating effective interactions between isolated spin qubits and to enable the preparation
of non-classical states of motion of a macroscopic object.

Time and Place: Friday, 17th November 2017, 11:00 h, Max Planck Institute for the Science of Light, Seminar Room A.1.500, Staudtstr. 2, 91058 Erlangen