Direct detection of quantum non-Gaussian light from a dispersively coupled single atom

TL;DR

This paper demonstrates that quantum non-Gaussian light can be reliably detected from a dispersively coupled single atom using single-photon detection, even under noisy conditions and with significant cavity leakage.

Contribution

It introduces a method to verify quantum non-Gaussianity via single-photon detection, overcoming challenges of noise and cavity leakage in atom-cavity systems.

Findings

Quantum non-Gaussian light can be detected despite noise.

Negativity of the Wigner function is not necessary for non-Gaussianity.

Detection is feasible with large cavity leakage at increased measurement times.

Abstract

Many applications in quantum communication, sensing and computation need provably quantum non-Gaussian light. Recently such light, witnessed by a negative Wigner function, has been estimated using homodyne tomography from a single atom dispersively coupled to a high-finesse cavity. This opens an investigation of quantum non-Gaussian light for many experiments with atoms and solid-state emitters. However, at their early stage, an atom or emitter in a cavity system with different channels to the environment and additional noise are insufficient to produce negative Wigner functions. Moreover, homodyne detection is frequently challenging for such experiments. We analyse these issues and prove that such cavities can be used to emit quantum non-Gaussian light employing single-photon detection in the Hanbury Brown and Twiss configuration and quantum non-Gaussianity criteria suitable for this measurement. We investigate in detail cases of considerable cavity leakage when the negativity of the Wigner function disappears completely. Advantageously, quantum non-Gaussian light can be still conclusively proven for a large set of the cavity parameters at the cost of overall measurement time, even if noise is present.