Experimental Demonstration of Negative-Valued Polarization Quasi-Probability Distribution

TL;DR

This paper experimentally demonstrates the negativity of the polarization quasiprobability distribution for a coherent state using photon-number resolving detectors, revealing non-classical features previously unobserved due to detector limitations.

Contribution

First experimental observation of negativity in the polarization quasiprobability distribution using photon-number resolving detectors.

Findings

Negativity observed in polarization quasiprobability distribution.

Photon-number resolving detectors enable direct observation.

Supports non-classicality in quantum polarization states.

Abstract

Polarization quasiprobability distribution defined in the Stokes space shares many important properties with the Wigner function for the position and momentum. Most notably, they both give correct one-dimensional marginal probability distributions and therefore represent the natural choice for the probability distributions in classical hidden-variable models. In this context, negativity of the Wigner function is considered as a proof of non-classicality for a quantum state. On the contrary, the polarization quasiprobability distribution demonstrates negativity for all quantum states. This feature comes from the discrete nature of the Stokes variables; however, it was not observed in previous experiments, because they were performed with photon-number averaging detectors. Here we reconstruct the polarization quasiprobability distribution of a coherent state with photon-number resolving detectors, which allows us to directly observe for the first time its negativity.