Bose-Einstein Condensation of Quasi-Particles by Rapid Cooling

TL;DR

This paper introduces a universal method to achieve Bose-Einstein Condensation of quasi-particles, demonstrated experimentally with magnons, by rapidly cooling the phonon bath to induce disequilibrium and trigger condensation.

Contribution

It presents a novel approach for inducing BEC in quasi-particles through rapid phonon cooling, expanding the methods available for studying quantum condensates.

Findings

Successful experimental demonstration with magnons

Rapid cooling induces disequilibrium leading to BEC

Spectral redistribution triggers condensation

Abstract

The fundamental phenomenon of Bose-Einstein Condensation (BEC) has been observed in different systems of real and quasi-particles. The condensation of real particles is achieved through a major reduction in temperature while for quasi-particles a mechanism of external injection of bosons by irradiation is required. Here, we present a novel and universal approach to enable BEC of quasi-particles and to corroborate it experimentally by using magnons as the Bose-particle model system. The critical point to this approach is the introduction of a disequilibrium of magnons with the phonon bath. After heating to an elevated temperature, a sudden decrease in the temperature of the phonons, which is approximately instant on the time scales of the magnon system, results in a large excess of incoherent magnons. The consequent spectral redistribution of these magnons triggers the Bose-Einstein condensation.