Quasiprobabilities for Multipartite Quantum Correlations of Light

TL;DR

This paper introduces quasiprobabilities to effectively characterize and visualize quantum correlations in multimode light fields, even when traditional measures indicate classicality.

Contribution

The authors develop a new quasiprobability framework that detects quantum correlations beyond entanglement and discord in multimode quantum states.

Findings

Negativities in quasiprobabilities indicate quantum correlations.

Method visualizes quantum correlations in classically mixed states.

Applicable to states with positive Wigner functions and no entanglement.

Abstract

Regular quasiprobabilities are introduced for the aim of characterizing quantum correlations of multimode radiation fields. Negativities of these quantum-correlation quasiprobabilities are necessary and sufficient for any quantum correlation encoded in the multimode Glauber-Sudarshan P function. The strength of the method is demonstrated for a two-mode phase randomized squeezed-vacuum state. It has no entanglement, no quantum discord, a positive Wigner function, and a classical reduced single-mode representation. Our method clearly visualizes the quantum correlations of this state.