Evolution of room-temperature magnon gas toward coherent Bose-Einstein condensate

TL;DR

This study investigates how a magnon gas in a magnetic crystal evolves into a coherent Bose-Einstein condensate at room temperature, revealing the process of coherence formation through microwave radiation detection.

Contribution

It provides the first direct observation of the coherence development in a room-temperature magnon condensate using spectral analysis.

Findings

Magnon gas evolves to a state with coherence limited only by natural relaxation.

Coherence formation occurs during the evolution of the magnon radiation spectra.

Room-temperature magnon Bose-Einstein condensation is experimentally demonstrated.

Abstract

The appearance of spontaneous coherence is a fundamental feature of a Bose-Einstein condensate and an essential requirement for possible applications of the condensates for data processing and quantum computing. In the case of a magnon condensate in a magnetic crystal, such computing can be performed even at room temperature. So far, the process of coherence formation in a magnon condensate was inaccessible. We study the evolution of magnon radiation spectra by direct detection of microwave radiation emitted by magnons in a parametrically driven yttrium iron garnet crystal. By using specially shaped bulk samples, we show that the parametrically overpopulated magnon gas evolves to a state, whose coherence is only limited by the natural magnon relaxation into the crystal lattice.