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arXiv:2610.03965

Rydberg-mediated microwave-to-optical transduction with tunable bandwidth

Iason Tsiamis, David Petrosyan, Anders S. Sørensen

quant-phphysics.atom-phSubmitted Oct 2, 2026• Announced Oct 6, 2026• 0 citations
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Abstract

Coherent microwave-to-optical transduction is essential for hybrid quantum networks. Typical transducers, however, have bandwidths set by fixed device parameters and face efficiency-bandwidth tradeoffs. We propose a cavity-based microwave-to-optical transducer mediated by a collective Rydberg excitation, where external driving fields tune the conversion bandwidth in situ from narrowband, spectrally selective operation to broadband operation without modifying cavity parameters. Under impedance-matching conditions, the system operates as a continuous-wave phase-preserving linear transducer, maintaining both near-unit efficiency and quantum-limited added noise throughout the tunable bandwidth range.

Comments
6 pages, 3 figures, plus supplemental material

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Coherent microwave-to-optical transduction is essential for hybrid quantum networks. Typical transducers, however, have bandwidths set by fixed device parameters and face efficiency-bandwidth tradeoffs. We propose a cavity-based microwave-to-optical transducer mediated by a collective Rydberg excitation, where external driving fields tune the conversion bandwidth in situ from narrowband, spectrally selective operation to broadband operation without modifying cavity parameters. Under impedance-matching conditions, the system operates as a continuous-wave phase-preserving linear transducer, maintaining both near-unit efficiency and quantum-limited added noise throughout the tunable bandwidth range.
High-efficiency microwave-to-optical quantum transduction is crucial for quantum networks and distributed quantum computing. Cavity-based electro-optic transducers have been widely explored due to their cavity-enhanced conversion efficiency, albeit at the compromise of limited transduction bandwidth and strict frequency alignment requirements between microwave and optical modes. A recent advancement in meter-long superconducting electro-optic modulators (SEOM) has demonstrated conversion efficiency approaching that of the cavity-based transducers on a traveling-wave structure while maintaining a broad bandwidth of tens of gigahertz. This paper provides a further theoretical investigation into the dynamics of the microwave-to-optical conversion process in a traveling-wave geometry. Based on this analysis, we propose a traveling-wave electro-optic transducer design featuring near-unity conversion efficiency and tunable conversion frequency.
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Microwave-optical transducers and quantum memories are essential for quantum repeaters enabling a quantum internet. Despite advances in both technologies, integrating these functionalities remains challenging. Here, we theoretically propose and experimentally demonstrate an on-demand microwave-optical quantum transducer based on a Rydberg ensemble. Using cascaded electromagnetically induced transparency, we store microwave photons in a highly excited collective state and convert them into optical photons during retrieval. Leveraging an optical depth of millions for microwave photons and minimal single-photon-level dephasing, our transducer achieves around 90% area-normalized storage efficiency, 2.3 MHz bandwidth, and noise-equivalent temperature of 26 K under cavity-free conditions. Furthermore, our system is cryogenically compatible and extendable for high single-photon conversion efficiency without requiring optical cavity coupling. These findings advance practical on-demand quantum interfaces with broad applications across atomic and solid-state platforms. A quantum internet would link computers over optical fibers, which would require converting their signals into frequencies that can travel by fiber and storing those signals to keep them in sync. The authors built a proof-of-concept from a Rydberg ensemble of cold rubidium atoms, that does both jobs.
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A quantum transducer converts an input signal to an output probe at a distant frequency band while maintaining the quantum information with high fidelity, which is crucial for quantum networking and distributed quantum sensing and computing. In terms of microwave–optical quantum transduction, the state-of-the-art quantum transducers suffer low transduction efficiency from weak nonlinear coupling, wherein increasing pump power to enhance efficiency inevitably leads to thermal noise from heating. Moreover, we reveal that the efficiency-bandwidth product of a cavity electro-optical or electro-optomechanical transducer is fundamentally limited by pump power and nonlinear coupling coefficient, irrespective of cavity engineering efforts. To overcome this fundamental limit, we propose to noiselessly boost the transduction efficiency by consuming intraband entanglement (e.g., microwave–microwave or optical–optical entanglement in the case of microwave–optical transduction). Via a squeezer–coupler–antisqueezer sandwich structure, the protocol enhances the transduction efficiency to unity in the ideal lossless case, given an arbitrarily weak pump and nonlinear coupling. In practical cavity systems, our entanglement-assisted protocol surpasses the non-assisted fundamental limit of the efficiency-bandwidth product and reduces the threshold cooperativity for positive quantum capacity by a factor proportional to two-mode squeezing gain. Given a fixed cooperativity, our approach increases the broadband quantum capacity by orders of magnitude. The entanglement-assisted advantage is robust to ancilla loss and cavity detuning.