Does KPZ physics destroy order in two-dimensional polariton condensates
In plain words
A two-dimensional light-matter condensate that is constantly pumped and leaking was predicted to lose long-range coherence at very large distances, unlike an equilibrium superfluid. This prediction lacks a decisive experimental test.
Precise statement
For a 2D driven-dissipative condensate described by a stochastic complex Ginzburg-Landau equation, phase dynamics maps to the compact KPZ equation, predicting algebraic order only up to a length $L*$ growing exponentially with the inverse nonequilibrium coupling (Altman, Sieberer, Chen, Diehl, Toner 2015). Is the loss of algebraic order beyond $L*$ observed in exciton-polariton condensates, and what replaces it (vortex-dominated disorder or a KPZ-roughened phase)? Answer yes or no, with the large-distance correlation form.
What would settle it
Measurement of first-order coherence $g1(r, t)$ in a large uniform 2D polariton condensate showing the crossover from algebraic decay to KPZ or stretched-exponential scaling.
Status in the literature
Unverified note
$1\mathrm{D}$ KPZ scaling of the condensate phase was observed in 2022 (Fontaine et al., Nature); a 2026 PRL (Misko, Starkova, Lagoudakis, doi:10.1103/z3ty-255t) reports KPZ physics in optically confined continuous condensates, and its bearing on the $2\mathrm{D}$ question was not checked.