Bidirectional conversion between microwave and light via ferromagnetic magnons

TLDR

Coherent microwave–optical photon conversion at the single‑quantum level promises enhanced signal processing, quantum‑noise‑limited microwave amplification, and a route to long‑distance quantum communication. The study demonstrates bidirectional, coherent microwave–light conversion via ferromagnetic magnons and discusses potential efficiency‑enhancement schemes. The converter couples a microwave cavity mode and a ferromagnetic Kittel mode, enabling itinerant microwave and travelling optical fields to interact through strong hybridization mediated by Faraday and inverse Faraday effects. The conversion efficiency was theoretically modeled and experimentally measured, demonstrating coherent bidirectional conversion.

Abstract

Coherent conversion of microwave and optical photons in the single-quantum level can significantly expand our ability to process signals in various fields. Efficient up-conversion of a feeble signal in the microwave domain to the optical domain will lead to quantum-noise-limited microwave amplifiers. Coherent exchange between optical photons and microwave photons will also be a stepping stone to realize long-distance quantum communication. Here we demonstrate bidirectional and coherent conversion between microwave and light using collective spin excitations in a ferromagnet. The converter consists of two harmonic oscillator modes, a microwave cavity mode and a magnetostatic mode called Kittel mode, where microwave photons and magnons in the respective modes are strongly coupled and hybridized. An itinerant microwave field and a travelling optical field can be coupled through the hybrid system, where the microwave field is coupled to the hybrid system through the cavity mode, while the optical field addresses the hybrid system through the Kittel mode via Faraday and inverse Faraday effects. The conversion efficiency is theoretically analyzed and experimentally evaluated. The possible schemes for improving the efficiency are also discussed.