Phys. Rev. B 93, 174427 (2016)
At present, experiments with large-scale many-body quantum systems often rely on superconducting quantum circuits that use microwave photons. However, microwave photons are vulnerable to thermal noise, which hinders long-distance quantum communication between different locations. If an efficient means for conversion between microwave and optical photons could be realized, optical photons could be used for the communication instead. With this goal in mind, Ryusuke Hisatomi and collaborators have demonstrated bidirectional and coherent conversion between microwave and light using collective spin excitations in a ferromagnet. A spherical yttrium iron garnet (YIG) crystal with a diameter of 0.75 mm was placed in a microwave cavity to form a strongly coupled hybrid system between a spatially uniform magnetostatic mode, called the Kittel mode, and a microwave cavity mode. A static magnetic field of 310 mT was applied to the YIG crystal and a microwave field was coupled to the hybrid system through the microwave cavity, while a travelling optical field addressed the hybrid system through the Kittel mode. The conversion from microwave photons to optical photons was based on the Faraday effect, while the inverse conversion was based on the inverse Faraday effect. The maximum photon conversion efficiency from a laser with a wavelength of 1,550 nm to a microwave at the frequency of 10.8 GHz was 10−10.
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