Microwave-to-optical quantum transduction of photons for quantum interconnects

Abstract The quantum transduction, or equivalently quantum frequency conversion, is vital for realizing, e.g., quantum networks and distributed quantum computing. The microwave-to-optical quantum transduction is of interest in the field of superconducting quantum computing, since interconnecting dilution refrigerators is considered inevitable for realizing large-scale quantum computers with fault-tolerance. In this review, we overview recent theoretical and experimental studies on the quantum transduction between microwave and optical photons. We describe a generic theory for the quantum transduction employing the input-output formalism, from which the essential quantities characterizing the transduction, i.e., expressions for the transduction efficiency, added noise, and transduction bandwidth, are derived. We review major transduction methods that have been experimentally demonstrated, including the optomechanical, electro-optic, and ensemble-based transducers. We also briefly review recent experiments on the quantum transduction from superconducting qubit to optical photon, which is an important step toward quantum state transfer between distant superconducting qubits interconnected over optical fibers.