Certifying non-classicality and non-Gaussianity through optical parametric amplification

TL;DR

This paper introduces a practical method to certify non-Gaussianity in quantum light states using optical parametric amplification and standard intensity detectors, avoiding complex tomography.

Contribution

It demonstrates both theoretically and experimentally that optical parametric amplification with conventional detectors can replace photon-number resolving measurements for certifying non-Gaussianity.

Findings

Successfully certifies non-Gaussianity of heralded quasi-single-photon states

Uses mean photon number and second-order correlation for certification

Applicable to broadband multimode quantum states

Abstract

Non-Gaussian states of light are essential for numerous quantum information protocols; thus, certifying non-Gaussianity is crucial. Full quantum state tomography, commonly used for this purpose, is a complicated procedure and yields inconclusive results for strongly mixed states. Certifying non-Gaussianity through directly measurable parameters is a simpler alternative, typically achieved by measuring photon-number probabilities - either directly, using photon-number resolving detectors, or through Hanbury Brown--Twiss type measurements with single-photon detectors. Here, we demonstrate theoretically and experimentally that optical parametric amplification combined with conventional intensity detectors can effectively replace this approach without the need for photon-number resolution. In our method, we measure the mean photon number and the second-order correlation function for the amplified state. Using it, we successfully certify the non-Gaussianity of a heralded quasi-single-photon state. Since optical parametric amplification is a broadband and multimode process, our method provides a foundation for developing high-dimensional quantum technologies utilizing broadband multimode non-Gaussian states.