Observation of three-photon bound states in a quantum nonlinear medium

TL;DR

This paper reports the experimental observation of three-photon bound states in a quantum nonlinear medium mediated by Rydberg interactions, revealing complex photon-photon correlations and nonlinear phases.

Contribution

It demonstrates the creation and control of three-photon bound states and provides a theoretical framework describing their interactions.

Findings

Observation of three-photon bound states with shape-preserving wavefunctions

Measurement of photon bunching and nonlinear phase consistent with effective field theory

Evidence of a significant three-body force among photons in the medium

Abstract

Bound states of massive particles, such as nuclei, atoms or molecules, constitute the bulk of the visible world around us. In contrast, photons typically only interact weakly. We report the observation of traveling three-photon bound states in a quantum nonlinear medium where the interactions between photons are mediated by atomic Rydberg states. Photon correlation and conditional phase measurements reveal the distinct bunching and phase features associated with three-photon and two-photon bound states. Such photonic trimers and dimers possess shape-preserving wavefunctions that depend on the constituent photon number. The observed bunching and strongly nonlinear optical phase are quantitatively described by an effective field theory (EFT) of Rydberg-induced photon-photon interactions, consistent with the presence of a substantial effective three-body force between the photons. These observations demonstrate the ability to realize and control strongly interacting quantum many-body states of light.