Correlations between a superconducting qubit and an optical photon

Quantum transducers offer a promising route to network remote superconducting qubits via optical fiber links. In recent years, optomechanical quantum transducers have attained performance suitable to realize quantum entanglement between microwave and optical photons [1] - a key capability to interface superconducting qubits with light. Building on this work, we report observation of correlations between the state of a superconducting qubit and an optical photon. Our experiment employs a modular architecture, connecting a superconducting qubit module to an optomechanical transducer module via a 0.8m superconducting microwave cable. We drive a microwave-optical photon pair generation process in the transducer module and employ a photon catch protocol in the qubit module to facilitate state transfer between the qubit and the flying microwave photon from the transducer. We observe correlations between the final qubit state and the detection of an optical photon, demonstrating a crucial step toward establishing quantum entanglement between superconducting qubits and light. We discuss ongoing progress and challenges in realizing hybrid entanglement and in extending this approach to entangle remote superconducting qubits over optical networks.

[1] Meesala et. al. PRX 14, 031055 (2024)