Ultra-long-living magnons in YIG in the quantum limit

Magnonics is the field of science that deals with data carried by spin waves and their quanta, magnons, in magnetically ordered media. Single-crystal yttrium iron garnet (YIG) material is known for its exceptionally low magnetic damping, making it a preferred material for both fundamental experiments and RF devices. The magnon lifetime is crucial for quantum magnonics, as highlighted by recent advancements in the excitation and detection of single magnons [1] and the measurement of the Wigner function of a single magnon via a superconducting qubit. Previously, it has been reported that with a decrease in temperature, the magnetic damping increases in YIG, which is associated with defects and chemical contamination [2].

Here, we report the discovery of short-wavelength magnons with lifetimes exceeding 18 µs at millikelvin temperatures [3]. The experiment was performed on an ultra-pure single-crystal YIG sphere over a wide temperature range, from ambient down to 30 mK. These results pave 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.