Memory-assisted multimode microwave-to-optical transduction.

Microwave-to-optical quantum transducers will enable coherent interconnection between distant superconducting quantum devices. Ongoing explorations have shown promising results at single-photon levels. However, eliminating noise arising from the concurrence of weak transduced signals with intense pump pulses remains a challenge, requiring high-suppression filtering. Memory-assisted transduction offers a versatile noise-mitigation approach and enables on-demand retrieval of transduced signals. Here, we integrate a quantum memory protocol with transduction in a three-level atomic system. Leveraging zero-first-order Zeeman transitions at zero magnetic field, providing long optical and spin coherence times, and GHz-range hyperfine splitting, we use a low-doping concentration 171Yb3+:Y2SiO5 crystal at 30 mK. We achieve on-demand memory-assisted transduction with 0.4 (and 0.3) noise photons at a storage duration of 460 (and 620) μs. Further, we establish coherence via interference patterns and demonstrate multimode capacity, utilizing spin and optical inhomogeneous broadening. The on-demand retrieval enables qubit synchronization in quantum repeaters, while multimode capacity boosts entanglement generation rates.