High bandwidth, bidirectional microwave to telecom conversion using an electro-optic transducer operating at millikelvin temperatures

Long distance connectivity of superconducting qubits poses an interesting challenge because their fragile microwave quantum states need to be protected from thermal noise. A hybrid quantum network, which combines the advantages of microwave quantum information processing and the robustness of optical telecommunication, appears as the natural solution. In this context, coherent conversion between optical and microwave photons is the key ingredient.
We present a triply resonant electro-optic modulator [1] as a bidirectional and low noise microwave to optics converter. Our system is based on a LiNbO3 whispering gallery mode resonator coupled to a superconducting 3D microwave cavity. Unlike electro-opto-mechanical systems, a low frequency mechanical mediator is not needed, allowing for a 10 MHz conversion bandwidth and low added conversion noise of less than 1 quanta for continuous wave optical pump powers up to 25 µW.

[1] A. Rueda, et al., Optica 3, (2016).