Spectroscopy on a single nonlinear mode recognizes quantum states

TL;DR

This paper demonstrates that a single nonlinear quantum mode can effectively recognize quantum states through spectral analysis, offering an alternative to traditional quantum state tomography.

Contribution

It introduces a neuromorphic approach using a quantum nonlinear mode as a reservoir for quantum state recognition, reducing experimental complexity.

Findings

Spectral analysis of a nonlinear mode can identify quantum state parameters.

Linear regression on emission spectra suffices for recognizing squeezed states.

The method is effective even with complex sources like a degenerate OPO.

Abstract

Characterising optical quantum states is essential for the development of quantum technologies. While traditional approaches to perform full quantum state tomography are often experimentally demanding, neuromorphic architectures may provide an effective alternative. In this work, we demonstrate how a quantum nonlinear driven-dissipative mode is sufficient to act as a quantum reservoir. By analyzing the occupations at different frequencies in the emission spectrum, a linear regression suffices in many cases to recognize the relevant parameters of incident squeezed states. Beyond highlighting the general potential of this approach under continuous driving, we illustrate its effectiveness in an explicit nontrivial example where the source is a degenerate optical parametric oscillator (OPO), coupled to a nonlinear polariton microcavity.