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Nuclear Physics B - Proceedings Supplements

Macroscopic quantum mechanics: The coherent and squeezed transformations in superconductivity

S. Fubini, Alfredo Molinari

Published Nov 1, 1993• 1 citation
Publisher
DOI
10.1016/0920-5632(93)90371-c

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We theoretically investigate the macroscopic quantum coherence and the mechanical squeezing of a mechanical oscillator in a hybrid optomechanical system consisting of a suspended graphene sheet and an ultracold atomic ensemble trapped inside a Fabry-P\'erot cavity. In the study the vacuum is used to mediate an effective optomechanical coupling between the graphene oscillator and the cavity field driven by an external laser beam. We find that in the presence of this coupling, the macroscopic quantum coherence and the mechanical squeezing of the graphene sheet can be attained in a certain range of driving power. In particular, the quantum coherence in the optomechanical system can be transferred from the optical field to the mechanical oscillator. We also investigate in detail the spectrum and the squeezing of the output field and the attained results may be used to study the mechanical squeezing of a graphene sheet.
Macroscopic quantum phenomena, e.g., superconductivity and squeezing, are believed to result from entanglement of macroscopic numbers of particles. We report the first direct study of this kind of entanglement: we use discrete quantum tomography to reconstruct the joint quantum state of photon pairs extracted from polarization-squeezed light. Our observations confirm several predictions from spin-squeezing theory [Beduini et al., Phys. Rev. Lett. 111, 143601 (2013)], including strong entanglement and entanglement of all photon pairs within the squeezing coherence time. This photon-by-photon analysis may give insight into other macroscopic many-body systems, e.g., photon Bose-Einstein condensates.