Observation of the Bogoliubov dispersion relation in a fluid of light

TL;DR

This paper reports the first experimental observation of the Bogoliubov dispersion relation in a fluid of light, demonstrating a tunable platform for studying quantum fluid phenomena using atomic vapor.

Contribution

It introduces a novel method for measuring excitation spectra in photon fluids and confirms the Bogoliubov dispersion relation in a nonlinear atomic vapor system.

Findings

Observed Bogoliubov-like dispersion relation

Speed of sound scales with square root of fluid density

Atomic vapor system is versatile for quantum fluid studies

Abstract

Quantum fluids of light are photonic counterpart to atomic Bose gases and are attracting increasing interest for probing many-body physics quantum phenomena such as superfluidity. Two different configurations are commonly used: the confined geometry where a nonlinear material is fixed inside an optical cavity, and the propagating geometry where the propagation direction plays the role of an effective time for the system. The observation of the dispersion relation for elementary excitations in a photon fluid has proved to be a difficult task in both configurations with few experimental real izations. Here, we propose and implement a general method for measuring the excitations spectrum in a fluid of light, based on a group velocity measurement. We observe a Bogoliubov-like dispersion with a speed of sound scaling as the square root of the fluid density. This study demonstrates that a nonlinear system based on an atomic vapor pumped near resonance is a versatile and highly tunable platform to study quantum fluids of light.