📝 SummarXiv

Abstract

Coherence time is a key property of quantum systems, determining how long quantum information can be preserved. In solid-state platforms, this parameter is closely linked to the lifetime of quasiparticles that can store quantum information. For decades, magnons - quasiparticles arising from collective magnetization dynamics - have exhibited lifetimes below one microsecond at gigahertz frequencies, limiting their viability as quantum information carriers. Here, we report the discovery of short-wavelength magnons with lifetimes exceeding 18 {\mu}s at millikelvin temperatures. The experiment was performed on an ultra-pure single-crystal Yttrium Iron Garnet (YIG) sphere over a wide temperature range, from ambient down to 30 mK. These results directly confirm the theoretical prediction that the magnon lifetime in an ideal YIG crystal at zero temperature is infinite, paving the way for the engineering of lossless magnetic systems in which magnons will be employed as long-lived carriers of information for quantum gates and quantum storage.