title: Macroscopic quantum state analyzed particle by particle.
abstract: 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.
authors: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.
authors: Federica A
authors: FA
authors: Beduini
authors: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.
authors: Joanna A
authors: JA
authors: Zielińska
authors: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.
authors: Vito G
authors: VG
authors: Lucivero
authors: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.
authors: Yannick A
authors: YA
authors: de Icaza Astiz
authors: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.|ICREA-Institució Catalana de Recerca i Estudis Avançats, 08015 Barcelona, Spain.
authors: Morgan W
authors: MW
authors: Mitchell