Future quantum networks of distant superconducting microwave quantum processors demand the use of optical photons for low loss and low noise interconnects. Bridging the energy gap between microwave and optical photons, however, requires the use of a frequency converter. Here, we demonstrate a frequency converter that can add a single photon to the microwave field conditioned on the detection of an optical photon. The device consists of a hybrid lithium niobate - silicon gigahertz nanomechanical resonator acting as an intermediary between a microwave and optical channel via strong piezoelectric and optomechanical interactions. For pulsed microwave photon generation, we achieve a heralding rate of 15 Hz. Thermal noise added by optical absorption in the device amounts to less than 2 microwave photons. Additionally, we measure a microwave-to-optical conversion efficiency of 5% under continuous wave operation. Finally, we discuss necessary steps for increasing the heralding rate and reducing thermal noise. Improving the device performance and system efficiency should pave the way for entangling two distant microwave-frequency quantum nodes through joint measurement on optical photons from a pair of transducers.
*This work was primarily supported by the U.S. Army Research Office (ARO) Cross-Quantum Systems Science & Technology (CQTS) program (Grant No. W911NF-18-1-0103), the National Science Foundation CAREER award No. ECCS-1941826, the Airforce Office of Scientific Research (AFOSR) (MURI No. FA9550- 17-1-0002 led by CUNY), and the David and Lucille Packard Fellowship. A.H.S.-N. acknowledges support via a Sloan Fellowship. The authors also wish to thank NTT Research and Amazon Web Services Inc. for their financial support. Some of this work was funded by the U.S. Department of Energy through Grant No. DE-AC02-76SF00515 and via the Q-NEXT Center. Device fabrication was performed at the Stanford Nano Shared Facilities (SNSF) and the Stanford Nanofabrication Facility (SNF), supported by the NSF award ECCS-2026822.
