Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode

TL;DR

This paper demonstrates a method to generate strongly correlated photon states using weak coupling and dissipation, leveraging collective nonlinear interactions in an atomic ensemble to produce nonclassical light.

Contribution

It introduces a novel approach to create correlated photons with weak coupling and dissipation, avoiding the need for strong quantum emitter coupling.

Findings

Observed strong photon bunching and anti-bunching effects

Achieved correlated photon states with less dissipation than uncorrelated photons

Demonstrated collective nonlinear interactions in atomic ensembles

Abstract

Photons in a nonlinear medium can repel or attract each other, resulting in a strongly correlated quantum many-body system. Typically, such strongly correlated states of light arise from the extreme nonlinearity granted by quantum emitters that are strongly coupled to a photonic mode. However, in these approaches, unavoidable dissipation, like photon loss, blurs nonlinear quantum effects. Here, we generate strongly correlated photon states using only weak coupling and taking advantage of dissipation. We launch light through an ensemble of non-interacting waveguide-coupled atoms, which induce correlations between simultaneously arriving photons through collectively enhanced nonlinear interactions. These correlated photons then experience less dissipation than the uncorrelated ones. Depending on the number of atoms, we experimentally observe strong photon bunching or anti-bunching of the transmitted light. This realization of a collectively enhanced nonlinearity may turn out transformational for quantum information science and opens new avenues for generating nonclassical light, covering frequencies from the microwave to the X-ray regime.