Generating Microwave-Optical Bell Pairs for Quantum Transduction Using Kerr Nonlinearity

Microwave-optical quantum transducers are essential for building quantum networks, as they interface remote computational nodes operating at disparate frequencies. In addition to direct frequency conversion, transduction can also be achieved through quantum teleportation using microwave-optical photon Bell pairs. Current entanglement-based transduction schemes rely on the Spontaneous Parametric Down Conversion (SPDC) process, which limits entanglement fidelity and generation probability by producing unwanted higher-excitation pairs in the output. Here, we propose a pulsed SPDC scheme that incorporates strong Kerr non-linearity in the microwave mode. This non-linearity causes higher excitations to become far detuned due to anharmonicity in the energy levels, allowing the system to be pulse-driven to produce single photon pairs in the output with optimized pulse length and driving strength. The Bell fidelity of the single photon pairs can be further protected against loss using dual-rail encoding and post-selection. In this setting, our pulsed non-linear scheme can ideally generate photon pairs with near-unit Bell fidelity at near-unit success probability. Considering the limited non-linearity and intrinsic loss in the experiment, our scheme can still produce photon pairs with a Bell fidelity exceeding 0.9, at a success probability more than ten times higher than that achievable by traditional SPDC sources.