Proposal for a microwave photon to optical photon converter based on traveling magnons in thin magnetic films

In this work, we propose a concept of a microwave to optical photon converter for applications in Quantum Information (QI) that is based on travelling magnons in a thin magnetic film. The converter employs an epitaxially grown Bi-substituted yttrium iron garnet (Bi-YIG) film as the medium for propagation of travelling magnons (spin waves). The conversion is achieved through coupling of magnons to guided optical modes of the film. We evaluate the conversion efficiency for this device theoretically. Our prediction is that it will be larger by at least four orders of magnitude than experimentally obtained in a similar process exploiting a uniform magnetization precession mode in a YIG sphere. By creating an optical resonator of a large length from the film (such that the traveling magnon decays before forming a standing wave over the resonator length) one will be able to further increase the efficiency by several orders of magnitude, potentially reaching a value similar to achieved with opto-mechanical resonators. An important advantage of the suggested concept of the QI devices based on travelling spin waves is a perfectly planar geometry compatible with the optical lithography process and a possibility of implementing the device as a hybrid opto-microwave chip.