Observation of KPZ universal scaling in a one-dimensional polariton condensate

TL;DR

This paper experimentally demonstrates that the phase evolution in a driven-dissipative one-dimensional polariton condensate exhibits KPZ universality, revealing fundamental out-of-equilibrium behaviors and broadening understanding of universal dynamics in open quantum systems.

Contribution

The study provides the first direct experimental evidence of KPZ universality in a polariton condensate's phase dynamics, supported by theoretical analysis and scaling law measurements.

Findings

KPZ space-time scaling laws observed in polariton condensate

Resilience of KPZ dynamics to space-time vortices

Fundamental differences between out-of-equilibrium and equilibrium condensates

Abstract

Revealing universal behaviors is a hallmark of statistical physics. Phenomena such as the stochastic growth of crystalline surfaces, of interfaces in bacterial colonies, and spin transport in quantum magnets all belong to the same universality class, despite the great plurality of physical mechanisms they involve at the microscopic level. This universality stems from a common underlying effective dynamics governed by the non-linear stochastic Kardar-Parisi-Zhang (KPZ) equation. Recent theoretical works suggest that this dynamics also emerges in the phase of out-of-equilibrium systems displaying macroscopic spontaneous coherence. Here, we experimentally demonstrate that the evolution of the phase in a driven-dissipative one-dimensional polariton condensate falls in the KPZ universality class. Our demonstration relies on a direct measurement of KPZ space-time scaling laws, combined with a theoretical microscopic analysis that consistently reveals the other key signatures of this universality class, together with the possible resilience of KPZ dynamics to the presence of space-time vortices. Our results highlight fundamental physical differences between out-of-equilibrium condensates and their equilibrium counterparts, and open a new paradigm for exploring universal behaviors in open systems.