Enhanced magnon lifetimes in out-of-equilibrium quantum magnonics*

Coupling magnons to other degrees of freedom in hybrid architectures presents a promising platform for advances in technologies for information processing and sensing. However, the relatively short magnon lifetimes encountered in such contexts, typically on the order of 100 ns in the quantum regime, are a limiting factor for experiments aiming to explore and exploit the quantum nature of magnons. We demonstrate that the lifetime of magnons in the magnetostatic mode of a ferrimagnetic sphere can be enhanced in-situ by around 30% by strongly pumping at an appropriate frequency, suggestive of the saturation of a bath of two-level systems (TLSs) [1]. Studying the resulting dynamics indicates evidence of lifetimes much longer than those of the other components of the hybrid system such as the magnetostatic mode. Consequently, the TLS bath remains excited while other elements of the hybrid system have relaxed into the ground state. Experiments in the quantum regime of magnonics, enabled via coherent coupling to a superconducting qubit, can thus be performed in an out-of-equilibrium state with an enhanced magnon lifetime.

[1] Y. Tabuchi et al., Phys. Rev. Lett. 113, 083603 (2014).