Quantum Nanomechanics -from levitation to many-body spin-spin interactions
Dr. Jan Gieseler (Deparment of Physics, Harvard University, Cambridge, MA, USA)

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>10^5). 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.