Repulsive photons in a quantum nonlinear medium

TL;DR

This paper introduces a method for coherently controlling strongly interacting photons, including repulsive interactions, in a quantum nonlinear medium using atomic states and Rydberg levels, enabling studies of quantum light matter.

Contribution

It presents a novel approach to engineer and control repulsive photon interactions in a quantum nonlinear medium, extending quantum optics capabilities.

Findings

Demonstrated both repulsive and attractive photon interactions

Measured two- and three-photon correlation functions

Observed signatures of interference and self-ordering

Abstract

The ability to control strongly interacting light quanta (photons) is of central importance in quantum science and engineering. Recently it was shown that such strong interactions can be engineered in specially prepared quantum optical systems. Here, we demonstrate a method for coherent control of strongly interacting photons, extending quantum nonlinear optics into the domain of repulsive photons. This is achieved by coherently coupling photons to several atomic states, including strongly interacting Rydberg levels in a cold Rubidium gas. Using this approach we demonstrate both repulsive and attractive interactions between individual photons and characterize them by the measured two- and three-photon correlation functions. For the repulsive case, we demonstrate signatures of interference and self ordering from three-photon measurements. These observations open a route to study strongly interacting dissipative systems and quantum matter composed of light such as a crystal of individual photons.