Kinetic theory of non-equilibrium condensation of microcavity polaritons

TL;DR

This paper develops a kinetic theory for microcavity polaritons considering Coulomb and phonon interactions, revealing how quantum fluctuations and system size influence polariton condensation.

Contribution

It introduces a comprehensive kinetic model that accounts for particle conservation and collective excitations, providing new insights into the limits of polariton condensation.

Findings

Condensate fraction remains below 1 even far above threshold.

Quantum fluctuations deplete the condensate at high excitation intensities.

Condensation is suppressed in systems larger than 100 microns due to fluctuations.

Abstract

We develop a kinetic theory of microcavity polaritons in presence of both Coulomb and polariton-phonon interaction, obeying particle number conservation. We study the growth of a macroscopic population of condensed particles in the lowest polariton state, under steady-state incoherent excitation of higher energy states. The collective excitation spectrum, resulting from the Coulomb Hamiltonian treated within the Hartree-Fock-Bogolubov framework, strongly influences the polariton condensation kinetics. In particular, for values of the excitation intensity above the condensation threshold, scattering from the condensate into the collective excitation modes results in strong quantum fluctuations that deplete the condensate. A numerical evaluation based on a few-level scheme shows that the condensate fraction is expected to be lower than 1 even far above threshold. With increasing system size, the role of the polariton quantum fluctuations becomes dominant, eventually preventing condensation to occur for system size larger than 100 micron.