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 spinsqueezing
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.
CitationBeduini, Federica A. [et al.]. Macroscopic Quantum State Analyzed Particle by Particle. "Physical Review Letters", 27 Març 2015, vol. 114, núm. 120402.
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