On-chip microwave-to-optical transduction with ¹⁷¹Yb³⁺:YVO₄at single photon levels

Microwave-to-optical transduction of single photons will play an essential role in interconnecting future superconducting quantum devices and enable a hybrid quantum network connecting disparate physical platforms. To perform efficient transduction that bridges five orders of magnitude in energy difference, a material with nonlinearity must be integrated into a system with that allows interfacing with both optical and microwave photons. In this work, we use ¹⁷¹Yb³⁺ ions doped in YVO₄, and demonstrate an on-chip microwave-to-optical transducer with device efficiency of about a percent, 1.2 added noise, 500 kHz bandwidth, and kHz-level repetition rate. This is enabled by the large intrinsic nonlinearity of this material, which we show to be 3 to 4 orders of magnitude larger than LiNbO₃. Furthermore, due to the fixed nature of the atomic frequencies and lack of a high-finesse optical cavity, we demonstrate the interconnection of two nominally identical devices. Specifically, the transduced optical photons from two simultaneously operated transducers are interfered to mimic remote entanglement protocols, or one of the transducers is operated in the reverse optical-to-microwave transduction mode to mimic optical control and readout of superconducting qubits. These results establish rare-earth ions doped in solids as a suitable material platform for transduction and pave the way for efficient quantum transduction.