Local-oscillator-agnostic squeezing detection

TL;DR

This paper introduces a new framework for detecting nonclassicality in continuous-variable quantum systems that does not require a known reference signal, enhancing robustness and sensitivity in quantum measurements.

Contribution

It develops a novel class of nonclassicality criteria based on partial normal ordering, applicable with arbitrary local oscillator states in homodyne detection.

Findings

Framework is robust against nonclassical local oscillators

Enhanced sensitivity over standard techniques

Applicable in quantum metrology and information

Abstract

We address the problem of measuring nonclassicality in continuous-variable bosonic systems without having access to a known reference signal. To this end, we construct broader classes of criteria for nonclassicality which allow us to investigate quantum phenomena regardless of the quantumness of selected subsystems. Such witnesses are based on the notion of partial normal ordering. This approach is applied to balanced homodyne detection using arbitrary, potentially nonclassical local oscillator states, yet only revealing the probed signal's quantumness. Our framework is compared to standard techniques, and the robustness and advanced sensitivity of our approach is shown. Therefore, a widely applicable framework, well-suited for applications in quantum metrology and quantum information, is derived to assess the quantum features of a photonic system when a well-defined coherent laser as a reference state is not available in the physical domain under study.