Towards integrating a coherent microwave single-photon source with a high-throughput electro-optic transducer

Efficient, low-noise electro-optic transduction is critical for enabling long-distance connectivity between superconducting qubits. We have recently demonstrated a membrane-based opto-electromechanical transducer achieving 7 kHz efficiency-bandwidth-duty-cycle product with 3-photon added noise, approaching quantum-limited operation in both upconversion and downconversion [1]. However, a key challenge is producing quantum states encoded in a long duration pulse compatible with the transducer's approximately 20 kHz bandwidth. In this presentation, I will share results from our initial integration experiments combining a narrowband source with the transducer and discuss measurements performed at the single-photon power regime. The source architecture incorporates two 3D microwave cavities coupled through a transmon qubit, which serves dual roles: providing nonlinearity for single-photon generation and enabling four-wave mixing for quantum state transfer between cavities. This quantum source has a high-coherence storage cavity (~1 ms), high-fidelity single-photon state preparation, tunable coupling, and frequency-tunable readout for interfacing with our fixed-frequency transducer. Finally, I will address the current experimental challenges we face in achieving optimal system performance for quantum state conversion.

[1] M.Urmey et al. (2025). High-throughput electro-optic upconversion and downconversion with few-photon added noise. arXiv:2507.09873