Bidirectional and efficient conversion between microwave and optical light

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R. W. Andrews, R. W. Peterson, T. P. Purdy, K. Cicak, R. W. Simmonds, C. A. Regal, and K. W. Lehnert Nature Physics 10, 321-326 (2014)

Hybrid quantum systems that allow for the transduction between different operating regimes and different physical systems are key enabling technologies for complex quantum systems. A microwave-to-optical converter in a quantum information network could be useful to link quantum processors through low-loss optical fibres and enabling a large-scale quantum network. However, no current technology can convert low- frequency microwave signals into high-frequency optical signals while preserving their quantum state.

In their work, Andrews and co-workers demonstrate a converter that provides a bidirectional, coherent and efficient link between the microwave and optical portions of the electromagnetic spectrum. The converter is used to transfer classical signals between microwave and optical light with conversion efficiencies of ∼10%, and achieve performance sufficient to transfer quantum states if the device were further precooled from its current 4 K operating temperature to temperatures below 40 mK. The implementation attains a conversion efficiency of four orders of magnitude over previous efforts.