Experimental test of nonclassicality criteria

TL;DR

This paper experimentally investigates the nonclassical nature of phase-diffused squeezed states, demonstrating that they are nonclassical even without observable squeezing, and evaluates the effectiveness of various nonclassicality criteria.

Contribution

It provides experimental evidence that the P function criterion reliably detects nonclassicality in phase-diffused states, surpassing other criteria that sometimes fail.

Findings

P function criterion detects nonclassicality in all phase-diffused states

Higher-order squeezing criteria sometimes fail to identify nonclassicality

Phase-diffused squeezed states can be nonclassical without observable squeezing

Abstract

We experimentally examine the nonclassical character of a class of non-Gaussian states known as phase-diffused squeezed states. These states may show no squeezing effect at all, and therefore provide an interesting example to test nonclassicality criteria. The characteristic function of the Glauber-Sudarshan representation (P function) proves to be a powerful tool to detect nonclassicality. Using this criterion we find that phase-diffused squeezed states are always nonclassical, even if the squeezing effect vanishes. Testing other criteria of nonclassicality based on higher-order squeezing and the positive semidefinitness of special matrices of normally ordered moments, it is found that these criteria fail to reveal the nonclassicality for some of the prepared phase-diffused squeezed states.