Magnon dark modes and gradient memory

TLDR

Hybrid quantum systems aim to extend superconducting circuit coherence by coupling to long‑lived spin degrees of freedom, with single‑crystal yttrium iron garnet emerging as a promising platform that supports highly coherent magnon modes enabling precise tuning. By engineering dissipation, the authors create a non‑Markovian interaction between magnons and microwave cavity photons, allowing a magnon gradient memory that stores information in dark modes decoupled from the cavity, thereby preserving long lifetimes. This approach demonstrates a promising route to long‑lifetime, multimode quantum memories.

Abstract

Abstract Extensive efforts have been expended in developing hybrid quantum systems to overcome the short coherence time of superconducting circuits by introducing the naturally long-lived spin degree of freedom. Among all the possible materials, single-crystal yttrium iron garnet has shown up recently as a promising candidate for hybrid systems, and various highly coherent interactions, including strong and even ultrastrong coupling, have been demonstrated. One distinct advantage in these systems is that spins form well-defined magnon modes, which allows flexible and precise tuning. Here we demonstrate that by dissipation engineering, a non-Markovian interaction dynamics between the magnon and the microwave cavity photon can be achieved. Such a process enables us to build a magnon gradient memory to store information in the magnon dark modes, which decouple from the microwave cavity and thus preserve a long lifetime. Our findings provide a promising approach for developing long-lifetime, multimode quantum memories.