Continuous sampling of the squeezed state nonclassicality

TL;DR

This paper introduces a continuous phase sampling method for directly measuring the nonclassicality quasiprobability of squeezed light, enabling unconditional verification of quantum properties without phase-locking errors.

Contribution

It presents a novel continuous sampling technique for the regularized P function of squeezed states, improving nonclassicality detection accuracy and universality over traditional discrete methods.

Findings

Negativities in the quasiprobability indicate nonclassicality.

The method allows unconditional verification without phase-locking.

Sampling is effective for various quantum states.

Abstract

We report the direct -- continuous in phase -- sampling of a regularized $P$ function, the so-called nonclassicality quasiprobability, for squeezed light. Through their negativities, the resulting phase-space representation uncovers the quantum character of the state. In contrast to discrete phase-locked measurements, our approach allows an unconditional verification of nonclassicality by getting rid of interpolation errors due to fixed phases. To realize the equal phase distribution of measured quadratures, a data selection is implemented with quantum random numbers created by measuring the vacuum noise. The continuously measured squeezed field was generated in an optical parametric amplifier. Suitable pattern functions for obtaining the regularized $P$ function are investigated. The significance of detecting negativities in our application is determined. The sampling of nonclassicality quasiprobabilities is shown to be a powerful and universal method to visualize quantum effects within arbitrary quantum states.