Microwave to optical photon conversion by means of travelling-wave magnons in YIG films

In this work we study theoretically the efficiency of a travelling magnon based microwave to optical photon converter for applications in Quantum Information (QI). The converter employs an epitaxially grown yttrium iron garnet (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. The total microwave to optical photon conversion efficiency is found to be larger than in a similar process employing a YIG sphere by at least 4 orders of magnitude. 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. Also, as a spin-off result, it is shown that isolation of more that 20 dB with direct insertion losses about 5 dBm can be achieved with YIG film based microwave isolators for applications in Quantum Information. An important advantage of the suggested concept of the QI devices based on travelling spin waves is a perfectly planar geometry and a possibility of implementing a the device as a hybrid opto-microwave chip.

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