Optomechanical backaction processes in a bulk rare-earth doped crystal

We investigate a novel hybrid system composed of an ensemble of room temperature rare-earth ions embedded in a bulk crystal, intrinsically coupled to internal strain via the surrounding crystal field. We evidence the generation of a mechanical response under resonant light excitation. Thanks to an ultra-sensitive time- and space-resolved photodeflection setup, we interpret this motion as the sum of two resonant optomechanical backaction processes: a conservative, piezoscopic process induced by the optical excitation of a well-defined electronic configuration, and a dissipative, non-radiative photothermal process related to the phonons generated throughout the atomic population relaxation. Parasitic heating processes, namely off-resonant dissipative contributions, are absent. This work demonstrates an unprecedented level of control of the conservative and dissipative relative parts of the optomechanical backaction, confirming the potential of rare-earth-based systems as promising hybrid mechanical systems.

Entanglement-assisted atomic clock beyond the projection noise limit

We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 10^5 cold cesium atoms, and for the first time operate an atomic clock improved by spin squeezing beyond the projection noise limit in a proof-of-principle experiment. For a clock-interrogation time of 10 mus the experiments show an improvement of 1.1 dB in the signal-to-noise ratio, compared to the atomic projection noise limit.