Ultra-long-living magnons in the quantum limit

TL;DR

This paper reports the discovery of magnon lifetimes exceeding 18 microseconds in yttrium iron garnet, significantly surpassing previous limits and highlighting their potential for quantum information processing.

Contribution

It demonstrates ultra-long magnon coherence times in a solid-state system at millikelvin temperatures, challenging prior assumptions about magnon dissipation.

Findings

Magnon relaxation times of nearly 20 microseconds at 30 mK.

Short-wavelength magnons exhibit two orders of magnitude longer lifetimes.

Results suggest magnons can serve as long-lived quantum information carriers.

Abstract

Solid-state platforms based on bosonic quasiparticles offer a compelling route toward on-chip quantum information technologies scalable to nanometer dimensions. Coherence time, a key figure of merit for any quantum system, is fundamentally limited by the lifetime of quasiparticles that store quantum information. For magnons - bosonic excitations of collective magnetization dynamics - it has long been reported that their lifetime does not exceed a few hundred nanoseconds, placing a stringent constraint on their use in quantum architectures. Here, we demonstrate magnon lifetimes exceeding 18 {\mu}s. Experiments performed on single-crystal yttrium iron garnet spheres cooled to 30 mK reveal relaxation times of short-wavelength magnons nearly two orders of magnitude longer than previously observed. These findings overturn the established view of magnon dissipation limits, positioning magnons as viable, long-lived information carriers for solid-state quantum computing.