Critical fluctuations in a confined driven-dissipative quantum condensate

TL;DR

This paper reports the experimental observation and theoretical analysis of critical fluctuations, including number fluctuations and mode competition, in a non-equilibrium polariton Bose-Einstein condensate near the condensation threshold, revealing quantum critical behavior.

Contribution

It provides the first combined experimental and theoretical study of critical fluctuations at the condensation threshold in a driven-dissipative quantum condensate, highlighting quantum effects in mode competition.

Findings

Observation of critical fluctuations near the condensation threshold

Identification of quantum mode competition analogous to laser mode hopping

Classical noise is insufficient to explain the observed phenomena

Abstract

Phase fluctuations determine the low-energy properties of quantum condensates. However, at the condensation threshold, both density and phase fluctuations are relevant. While strong emphasis has been given to the investigation of phase fluctuations, which dominate the physics of the quantum system away from the critical point -- number fluctuations have been much less explored, even in thermal equilibrium. In this work, we report experimental observation and theoretical description of fluctuations in a circularly-confined non-equilibrium Bose-Einstein condensate of polaritons near the condensation threshold. We observe critical fluctuations, which combine the number fluctuations of a single-mode condensate state and competition between different states. The latter are analogous to mode hopping in photon lasers. Our theoretical analysis indicates that this phenomenon is of a quantum character, while classical noise of the pump is not sufficient to explain the experiments. The manifestation of a critical quantum state competition unlocks new possibilities for the study of condensate formation while linking to practical realizations in photonic lasers.