title: Nonclassicality Criteria in Multiport Interferometry.
abstract: Interference lies at the heart of the behavior of classical and quantum light. It is thus crucial to understand the boundaries between which interference patterns can be explained by a classical electromagnetic description of light and which, on the other hand, can only be understood with a proper quantum mechanical approach. While the case of two-mode interference has received a lot of attention, the multimode case has not yet been fully explored. Here we study a general scenario of intensity interferometry: we derive a bound on the average correlations between pairs of output intensities for the classical wavelike model of light, and we show how it can be violated in a quantum framework. As a consequence, this violation acts as a nonclassicality witness, able to detect the presence of sources with sub-Poissonian photon-number statistics. We also develop a criterion that can certify the impossibility of dividing a given interferometer into two independent subblocks.
authors.affiliation: Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Rigovacca
authors.affiliation: Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.|School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore.|Complexity Institute, Nanyang Technological University, 637723, Singapore.
authors.forename: C
authors.initials: C
authors.lastname: Di Franco
authors.affiliation: Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: B J
authors.initials: BJ
authors.lastname: Metcalf
authors.affiliation: Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: I A
authors.initials: IA
authors.lastname: Walmsley
authors.affiliation: Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: M S
authors.initials: MS
authors.lastname: Kim