Pump Free Microwave-Optical Quantum Transduction

Abstract

Distributed quantum computing involves superconducting computation nodes operating at microwave frequencies, which are connected by long-distance transmission lines that transmit photons at optical frequencies. Quantum transduction, which coherently converts between microwave and optical (M-O) photons, is a critical component of such an architecture. Current approaches are hindered by the unavoidable problem of device heating due to the optical pump. In this work, we propose a pump-free scheme based on color centers that generates time-bin encoded M-O Bell pairs. Our scheme first creates spin-photon entanglement and then converts the spin state into a time-bin-encoded microwave photon using a strongly coupled Purcell-enhanced resonator. In our protocol, the microwave retrieval is heralded by detecting the microwave signal with a three-level transmon. We have analyzed the resulting Bell state fidelity and generation probability of this protocol. Our simulation shows that by combining a state-of-the-art spin-optical interface with our proposed strongly-coupled spin-microwave design, the pump-free scheme can generate M-O Bell pairs at a heralding rate exceeding one kilohertz with near-unity fidelity, which establishes the scheme as a promising source for M-O Bell pairs.

Figures (6)

• Figure 1: Schematic of the hybrid microwave-resonator–optical-cavity device for pump-free quantum transduction. The microwave resonator incorporates a diamond-sandwiched parallel-plate capacitor that enables strong coupling to a spin qubit in a one-dimensional photonic crystal cavity, thereby facilitating heralded generation of microwave–optical Bell pairs.
• Figure 2: (a) Illustration of the protocol with level schemes for the color center and a superconducting transmon qubit. The color center couples to an optical cavity and a microwave resonator. (b) Operation scheme in time sequence for spin-photon entanglement and microwave retrieval, where $\pi_{0r}$ represents a $\pi$-rotation in the $\ket{0},\ket{r}$ subspace of the three-level system.
• Figure 3: (a) Hybrid optical-cavity--microwave-resonator design demonstrating the feasibility of the pump-free quantum transduction protocol. The microwave resonator is modeled as a parallel LC circuit, with a coplanar waveguide (CPW) placed above it for signal input and readout. The resonator shown here is designed for the $^{117}$SnV$^-$ center. A one-dimensional photonic crystal cavity is positioned near the inductive-wire region of the resonator to achieve both strong microwave coupling and high optical cooperativity. (b,c) Simulation results at the center of the cavity (red dashed line in (a)) and the corresponding figures of merit for (b) the $^{117}$SnV$^-$ center and (c) the NV$^-$ center. For the fidelity calculation, we use $T_{1,\mathrm{t}} = 1~\mathrm{ms}$ and $T_{2,\mathrm{s}} = 2.5~\mathrm{ms}$ for the $^{117}$SnV$^-$ center, and $T_{2,\mathrm{s}} = 1~\mathrm{ms}$ for the NV$^-$ center bland20252dtransmonslifetimescoherenceharris2025highrondin_magnetometry_2014.
• Figure 4: Effective circuit diagram of the resonator coupled to a coplanar waveguide (CPW) transmission line. The circuit is conceptually equivalent to the model in Ref. Eichler2017.
• Figure 5: Figures of merit for selected spin positions (indicated by stars) in the optical cavity, evaluated for different color centers.