Abstract
Superconducting quantum processors are a leading platform for implementing practical quantum computation algorithms. Although superconducting quantum processors with hundreds of qubits have been demonstrated, their further scale-up is constrained by the physical size and cooling power of dilution refrigerators. This constraint can be overcome by constructing a quantum network to interconnect qubits hosted in different refrigerators, which requires microwave-to-optical transducers to enable low-loss signal transmission over long distances. Although various designs and demonstrations have achieved high-efficiency and low-added-noise transducers, a coherent photonic link between separate refrigerators has not yet been realized. Here we experimentally demonstrate coherent signal transfer between two superconducting circuits housed in separate dilution refrigerators, enabled by a pair of frequency-matched aluminium nitride electro-optic transducers connected via a 1-km telecom optical fibre. The optical frequency matching between two transducers is realized by an asymmetric photonic molecule design, and an overall 80 dB improvement in transduction efficiency over commercial electro-optic modulators is achieved, paving the way towards a fully quantum-enabled link. This work provides critical design guidelines for scalable superconducting quantum networks interconnected by photonic links.
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Data availability
The data shown in this paper are available via figshare at https://doi.org/10.6084/m9.figshare.31083652 (ref. 55).
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Acknowledgements
We acknowledge support from the Co-design Center for Quantum Advantage under DE-SC0012704 (H.X.T.), NSF’s National Quantum Virtual Laboratory programme under 2410725 (H.X.T.) and Yale Quantum Institute fellowship (Y.Z.). We would like to thank X. Han, S. Wang and W. Fu for refrigeration hardware installation, and Y. Sun, L. McCabe, K. Woods, Y. Shin, M. Rooks and S. Sohn for their assistance provided in the device fabrication. The fabrication of the devices was done at the Yale School of Engineering & Applied Science (SEAS) Cleanroom and the Yale Institute for Nanoscience and Quantum Engineering (YINQE). The TWPA used in this experiment is provided by IARPA and MIT Lincoln Laboratory.
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H.X.T. and Y.Z. conceived the idea and experiment. Y.Z. fabricated the devices with assistance from M.S., L.Y. and J.X. Y.Z. performed the measurements with assistance from Y.W. and C.L. Y.Z., Y.W., C.L. and H.X.T. analysed the data. Y.Z. and H.X.T. wrote the paper with inputs from all authors. H.X.T. supervised the project.
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Extended data
Extended Data Fig. 1 Surface charge distribution of the superconducting resonator.
The surface charge distribution of the superconducting resonator when excited with on-resonance microwave signals. The simulation is performed with Sonnet software. The charges are concentrated in the capacitor region, suggesting that the electric field is also confined at the capacitor. A π phase can be seen between the two rings due to the reversed polarity.
Extended Data Fig. 2 Fabrication process flow of an AlN transducer.
See Methods for detailed descriptions.
Extended Data Fig. 3 Experimental setup for transduction efficiency characterization.
See Methods for detailed descriptions.
Extended Data Fig. 4 Simulated effect of cladding thickness on geo and Qm.
(a) Schematic of the structure in the simulation. The cladding thickness tclad is used as the variable. (b) The simulated single-photon coupling rate geo at different thickness. (c) The simulated piezoelectric-limited microwave quality factor Qm at different thickness. The simulation is performed by using the COMSOL piezoelectricity module50. (d) The transduction efficiency is \(\eta \propto {g}_{{\rm{eo}}}^{2}{Q}_{{\rm{m}}}\). We thus use \({g}_{{\rm{eo}}}^{2}{{\rm{Q}}}_{{\rm{m}}}\) as the figure of merit to investigate the effect of cladding thickness on the transduction efficiency. It can be seen that \({g}_{{\rm{eo}}}^{2}{{\rm{Q}}}_{{\rm{m}}}\) does not drop substantially when cladding thickness increases. However, the thermal added noise can be well suppressed when the distance between superconductors and optical rings is larger. Therefore, using a larger cladding thickness can in principle reduce thermal added noise without compromising efficiency.
Extended Data Fig. 5 Experimental setup for noise measurement and 1-km photonic link.
See Methods for detailed descriptions.
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Zhou, Y., Wu, Y., Li, C. et al. A 1-km photonic link connecting superconducting circuits in two dilution refrigerators. Nat. Photon. (2026). https://doi.org/10.1038/s41566-026-01866-7
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DOI: https://doi.org/10.1038/s41566-026-01866-7
