Dispersion relation of the collective excitations in a resonantly driven polariton fluid

Petr Stepanov,Iacopo Carusotto,Jacqueline Bloch,Maxime Richard,Aristide Lemaître,Jean-Guy Rousset,Alberto Amo,Ivan Amelio,Anna Minguzzi

doi:10.1038/s41467-019-11886-3

Abstract

Exciton-polaritons in semiconductor microcavities constitute the archetypal realization of a quantum fluid of light. Under coherent optical drive, remarkable effects such as superfluidity, dark solitons or the nucleation of vortices have been observed, and can be all understood as specific manifestations of the condensate collective excitations. In this work, we perform a Brillouin scattering experiment to measure their dispersion relation omega ({bf{k}}) directly. The results, such as a speed of sound which is apparently twice too low, cannot be explained upon considering the polariton condensate alone. In a combined theoretical and experimental analysis, we demonstrate that the presence of an excitonic reservoir alongside the polariton condensate has a dramatic influence on the characteristics of the quantum fluid, and explains our measurement quantitatively. This work clarifies the role of such a reservoir in polariton quantum hydrodynamics. It also provides an unambiguous tool to determine the condensate-to-reservoir fraction in the quantum fluid, and sets an accurate framework to approach ideas for polariton-based quantum-optical applications.

Highlights

Exciton-polaritons in semiconductor microcavities constitute the archetypal realization of a quantum fluid of light
Their nonequilibrium character comes from the fact that they need to be continuously replenished by an external pump to compensate for ultrafast radiative losses
We find that the results differ strongly from the pure polariton condensate situation described by the generalized Gross–Pitaevskii equation (GGPE), like for example a speed of sound which is apparently twice too low

Summary

Introduction

Exciton-polaritons in semiconductor microcavities constitute the archetypal realization of a quantum fluid of light. For states in the upper branch of I0ðPÞ, the polariton density is organized into two large spatial structures: The highpolariton density is contained in a large diameter disk-shaped area at the center of the laser spot, separated from a low-density outer region by a sharp switching front (see examples in Supplementary Fig. 5).

Results

Conclusion