NonClassicality Criteria in Multiport Interferometry

TL;DR

This paper establishes classical bounds for intensity correlations in multiport interferometry and demonstrates how quantum sources can violate these bounds, serving as nonclassicality witnesses and providing new criteria for interferometer analysis.

Contribution

It derives classical bounds for multiport intensity correlations and introduces quantum violations as nonclassicality witnesses, extending understanding beyond two-mode interference.

Findings

Classical bounds on output intensity correlations are derived.

Quantum sources can violate these classical bounds.

A criterion for the inseparability of interferometer subblocks is developed.

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.