Quantum-enabled operation of a microwave-optical interface.

Solid-state microwave systems offer strong interactions for fast quantum logic and sensing but photons at telecom wavelength are the ideal choice for high-density low-loss quantum interconnects. A general-purpose interface that can make use of single photon effects requires < 1 input noise quanta, which has remained elusive due to either low efficiency or pump induced heating. Here we demonstrate coherent electro-optic modulation on nanosecond-timescales with only 0.1 6 − 0.01 + 0.02 microwave input noise photons with a total bidirectional transduction efficiency of 8.7% (or up to 15% with 0.4 1 − 0.02 + 0.02 ), as required for near-term heralded quantum network protocols. The use of short and high-power optical pump pulses also enables near-unity cooperativity of the electro-optic interaction leading to an internal pure conversion efficiency of up to 99.5%. Together with the low mode occupancy this provides evidence for electro-optic laser cooling and vacuum amplification as predicted a decade ago. Faithful conversion of quantum states between electrical circuits and light requires adding less than one input noise photon during conversion. Here, the authors demonstrate this based on coherent electro-optic upconversion with a transduction efficiency of 15%. [ABSTRACT FROM AUTHOR]