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arXiv:2512.05096

Pump Free Microwave-Optical Quantum Transduction

Fangxin Li, Jaesung Heo, Zhaoyou Wang, Andrew P. Higginbotham, Alexander A. High, Liang Jiang

quant-phSubmitted Dec 4, 2025• Announced Dec 5, 2025• 0 citations

v1 · Dec 4, 2025 v2 · Sep 14, 2026

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.

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The coherent conversion between microwave and optical photons, known as quantum transduction, is critical for connecting superconducting processors to optical networks. Existing methods are limited by complications associated with optical pumping. We propose a pump-free microwave-optical Bell-pair source for teleportation-based transduction. Using a spin or atomic system resonantly coupled to optical and microwave cavities, the scheme generates loss-robust heralded Bell pairs. Across color centers, atomic ensembles, and phonon-mediated systems, this assembly achieves kilohertz-range heralding rates with high fidelity.

A microwave-optical converter with high efficiency (>50%) and low added noise ( ≪ 1 photon) could enable the creation of scalable optical quantum networks. However, integrated converters demonstrated to date are too lossy or weakly non-linear to provide this performance. Here we develop a theory of microwave-optical conversion employing an ensemble of spin-bearing color centers strongly coupled to a photonic resonator and/or a superconducting microwave resonator. We find a counterintuitive operating point where microwave and optical photons are tuned to bare center/cavity resonances, which, compared to the weak-coupling limit, has much stronger non-linearity, offering high efficiency with reduced pump- and center-induced losses, and that is robust to inhomogeneous broadening. Taking color center and optical pump-induced losses into account, we predict ~ 95% efficiency and added noise ≪ 1 quanta at low ( μ W) pump powers for both Er- and T-centers in Si. Our results open new pathways to build quantum networks.

Scaling up superconducting quantum processors remains a central challenge for realizing fault-tolerant quantum computation. Although distributed architectures based on optical photons offer a promising route to scalability, they require an efficient microwave-to-optical quantum transducer that operates at cryogenic temperatures. Existing approaches typically rely on strong optical pumping, which induces undesirable heating and degrades single-photon coherence. Here, we propose a microwave-to-optical quantum transducer based on resonant scattering at a single color center embedded in a diamond optomechanical resonator. We show that strong coupling between the color center and the optical cavity enables coherent conversion at extremely weak pump powers on the order of 10 pW. The proposed scheme enables remote entanglement generation at a kilohertz-scale rate with a fidelity exceeding 0.9, demonstrating a viable pathway toward ultra-weak-pump and high-efficiency quantum transducers based on a solid-state defect.

Research into hybrid quantum systems is of great interest for quantum information processing; however, a key challenge is finding a controlled interface between a superconducting circuit and a lone solid-state qubit. The authors design a coherent quantum interface between a microwave cavity and a single nitrogen-vacancy center in a mechanical resonator made of diamond. Here the coupling between the quantized motion of the diamond beam and the cavity photons is due to dielectric interaction, not the traditional capacitive coupling, and is scalable to large arrays of resonators for e.g. a memory chip.

In quantum networks, robust and efficient frequency conversions of photons between microwave (MW) and optical regimes serve as a critical interface bridging superconducting quantum processors and optical communication channels. Recently, a topologically protected paradigm of state transfers, based on the topological nature of quantized light in Fock-state lattices (FSLs), has been demonstrated by a superconducting quantum circuit. However, its extension to quantum networks remains unexplored. Here we develop a topological single-photon MW–optics interface based on FSLs with a single nitrogen-vacancy (NV) center spin embedded in a photonic crystal cavity (PCC). The NV spin mediates the effective strong coupling between the optical PCC mode and a superconducting MW resonator via the adiabatic elimination of an intermediate acoustic mode. This scheme establishes a hybrid MW-NV-optics two-mode Jaynes-Cummings model, yielding a topological FSL. Under the significant constraint of optical mode decay, numerical simulations reveal that the MW-to-optics conversion efficiency can exceed 26% for an input five-photon MW Fock state. This work establishes a topological paradigm for hybrid quantum transduction, offering an efficient solid-state framework for constructing large-scale quantum networks.

We introduce a hybrid tripartite quantum system for strong coupling between a semiconductor spin, a mechanical phonon, and a microwave photon. Consisting of a piezoelectric resonator with an integrated diamond strain concentrator, this system achieves microwave-acoustic and spin-acoustic coupling rates

\sim

MHz or greater, allowing for simultaneous ultra-high cooperativities (

\sim 10^3

and

\sim 10^2

, respectively). From finite-element modeling and master equation simulations, we estimate photon-to-spin quantum state transfer fidelities exceeding 0.97 based on separately demonstrated device parameters. We anticipate that this device will enable hybrid quantum architectures that leverage the advantages of both superconducting circuits and solid-state spins for information processing, memory, and networking.