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Coherent control of a superconducting qubit using light

Nature Physics volume 21, pages 831–838 (2025)Cite this article

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Abstract

Quantum communications technologies require a network of quantum processors connected with low-loss and low-noise communication channels capable of distributing entangled states. Superconducting microwave qubits operating in cryogenic environments have emerged as promising candidates for quantum processor nodes. However, scaling these systems is challenging because they require bulky microwave components with high thermal loads that can quickly overwhelm the cooling power of a dilution refrigerator. Telecommunication frequency optical signals, however, can be fabricated in significantly smaller form factors to avoid challenges caused by high signal loss, noise sensitivity and thermal loads due to their high carrier frequency and propagation in silica optical fibres. Transduction of information by means of coherent links between optical and microwave frequencies is therefore critical to leverage the advantages of optics for superconducting microwave qubits, while also enabling superconducting processors to be linked with low-loss optical interconnects. Here, we demonstrate coherent optical control of a superconducting qubit. We achieve this by developing a microwave–optical quantum transducer that operates with up to 1.18% conversion efficiency with low added microwave noise, and we demonstrate optically driven Rabi oscillations in a superconducting qubit.

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Fig. 1: Transducer-driven superconducting qubit scheme.
Fig. 2: CEO-MOQT.
Fig. 3: Characterization of transducer performance.
Fig. 4: Evaluation of optically generated microwave noise in the transducer.
Fig. 5: Optical control of superconducting qubits.

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Data availability

Data shown in the main text (Figs. 2–5) and Extended Data Figs. 1–7 are available via Zenodo at https://doi.org/10.5281/zenodo.14628434 (ref. 41).

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Acknowledgements

The TWPA used in this work was provided by MIT Lincoln Laboratory. The qubit control code was built using the open-source quantum instrument control kit (QICK). The fabrication of these chips was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which is supported by the National Science Foundation under NSF award no. 1541959. We thank C.-H. Wang, Y. Wong, M. Zhang, C. Zhong and M. Haas for helpful discussions. This work was supported by the AFRL under award no. RCP06360 (H.K.W., J.H., D.B. and N.S.); NSF under award nos. EEC-1914583 (H.K.W. and N.S.), OMA-2137723 (D.B. and C.J.X.) OMA-1936118, ERC-1941583 and OMA-2137642 (L.J.); DARPA under award no. HR01120C0137 (D.B. and A.S.-A.); DoD under award no. FA8702-15-D-0001 (N.S.), DoE under award no. DE-SC0020376 (N.S.); AFOSR under award nos. FA9550-20-1 (D.Z.), FA9550-19-1-0399, FA9550-21-1-0209 (L.J.); ARO under award nos. W911NF-20-1-0248 (D.Z.), W911NF-23-1-0077 and W911NF-21-1-0325 (L.J.); and NTT Research, Packard Foundation under award no. 2020-71479 (L.J.). H.K.W. acknowledges financial support from the National Science Foundation Graduate Research Fellowship under grant no. 1745303. D.B. acknowledges financial support by the Intelligence Community Postdoctoral Fellowship. D.Z. acknowledges financial support from the HQI fellowship. E.B. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant no. 2141064. G.J. acknowledges financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC).

Author information

Author notes

  1. Jeffrey Holzgrafe

    Present address: Hyperlight Corporation, Cambridge, MA, USA

  2. Beatriz Yankelevich

    Present address: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA

  3. David Barton

    Present address: Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA

  4. Marco Colangelo

    Present address: Electrical and Computer Engineering Department, Northeastern University, Boston, MA, USA

  5. Matthew J. Reagor

    Present address: Google LLC, Mountain View, CA, USA

Authors and Affiliations

  1. Harvard John A. Paulson School for Engineering and Applied Sciences, Cambridge, MA, USA

    Hana K. Warner, Jeffrey Holzgrafe, David Barton, C. J. Xin, Neil Sinclair, Di Zhu, Amirhassan Shams-Ansari, Graham Joe & Marko Lončar

  2. Rigetti Computing, Berkeley, CA, USA

    Beatriz Yankelevich, Stefano Poletto, Eyob Sete, Brandon Langley & Matthew J. Reagor

  3. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA

    Emma Batson, Marco Colangelo & Karl K. Berggren

  4. Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA

    Liang Jiang

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Contributions

J.H. and H.K.W. designed the transducer. D.B., H.K.W., J.H. and C.J.X. fabricated the transducer with help from E.B. and M.C. for the Nb superconductor growth and A.S.-A. for fabrication development. Superconducting qubits were designed and fabricated by Rigetti Computing. H.K.W. built the experimental set-up with help from J.H. and B.Y. Measurements were designed by H.K.W., B.Y. and J.H. with help from S.P., N.S., D.Z., E.S., B.L., L.J., M.J.R. and M.L. The cryogenic measurement system was built and maintained by H.K.W., J.H., N.S., D.Z. and G.J. Measurements and data analysis were completed by H.K.W. H.K.W. wrote the manuscript with contributions from all authors.

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Correspondence to Hana K. Warner or Marko Lončar.

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Competing interests

J.H. and M.L. are currently involved in developing lithium niobate technologies at HyperLight Corporation. B.Y., S.P., E.S., B.L. and M.J.R. are or have been involved in developing quantum computing technology at Rigetti Computing. The remaining authors declare no competing interests.

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Extended data

Extended Data Fig. 1 Transducer grating couplers.

(a) Optical micrograph of grating couplers etched in TFLN cladded with SiO2. A Nb alignment grating is created around the couplers in order to help with coupling inside of the dilution refrigerator. (b) Cross section of grating couplers for transducer material stack. Light is coupled into the waveguide according to the phase matching condition \({{\rm{k}}}_{2}={{\rm{k}}}_{1}\sin \theta +2\pi {{\rm{n}}}_{{\rm{eff}}}/\Lambda\) where k = 2π/Λ is the wave-vector in the material propagating at angle θ and gratings are described by pitch Λ and separation δ. (c) Loss per grating measured through our device.

Extended Data Fig. 2 Electro-optic coupling rate.

We simulate the microwave-optical single photon coupling rate, g0, for (a) fully cladded and (b) plateau etch electrode geometries. (c) We see a 1.4× improvement in single photon coupling rate when comparing the plateau etch to a fully cladded device.

Extended Data Fig. 3 Schematic for CEO-MOQT and SC qubit measurements.

(a) Simplified schematic for microwave → optical conversion and (b) optical → microwave conversion. Here, solid lines correspond to electrical cabling and dotted lines correspond to optical fiber. (c) detailed schematic for the whole measurement system. Transducer components are highlighted in gold. Qubit components are highlighted in pink. (d) Definition of link losses (η) in the system.

Extended Data Fig. 4 Microwave resonator spectra and linewidths (plotted in gold) for measured on-chip optical pump powers.

(a) Microwave characterization during transduction efficiency measurements. Powers measured with pulsed optical pumps are enclosed in a black box. We selected our duty cycle for each pulsed pump power to maintain low thermal bath temperature, which allowed us to maintain a microwave linewidth ~ 10 MHz for our pulsed transduction efficiency measurements. (b) Microwave transmission during noise measurements.

Extended Data Fig. 5 Summary of all-RF qubit bring-up using power domain π-pulses.

We present (a) readout resonator transmission at 5.709 GHz, (b) qubit spectroscopy when the qubit is flux-biased to 3.690 GHz, (c) power Rabi oscillations reported in arbitrary voltage units, (d) Ramsey measurements, from which we extract a coherence time \({{{\rm{T}}}_{2}}^{* }=778\,{\rm{ns}}\), and (e) a lifetime measurement, from which we extract a lifetime of T1 = 8.42 μs.

Extended Data Fig. 6 Simulated microwave emission profiles for 100 ns pulses.

Pulse profiles are for square-wave input optical fields (blue) and sawtooth-wave input optical fields (pink).

Extended Data Fig. 7 Qubit performance while transducer is optically pumped.

We characterize (a) Qubit lifetime (T1), (b) coherence time (\({{{\rm{T}}}_{2}}^{* }\)), and (c) readout fidelity as a function of on-chip optical power with a single strong pump field (no optical idler) averaged over 5000 measurements. Errorbars correspond to the standard error over all repetitions. The top (pink) is measured with the qubit flux-biased to the transducer frequency (fMOQT) while the bottom (blue) is measured with the qubit flux-biased to the qubit maximum frequency (\({{\rm{f}}}_{\max }\)). We report the \({{\rm{T}}}_{1},{{{\rm{T}}}_{2}}^{* }\), and readout fidelity of the qubit while the laser is off as a dashed gold line, with the confidence interval shaded in gold. We measure the qubit while the laser is off-resonant with our optical modes (circles) and locked to the red optical resonance (triangles). We see that the qubit lifetimes (a), coherence times (b), and fidelities (c) do not experience degradation within the error of baseline measurements with increased optical power at the transducer flux bias (fCEO−MOQT = 3.71 GHz) or the qubit maximum frequency (\({{\rm{f}}}_{\max }=4.571\,{\rm{GHz}}\)).

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Warner, H.K., Holzgrafe, J., Yankelevich, B. et al. Coherent control of a superconducting qubit using light. Nat. Phys. 21, 831–838 (2025). https://doi.org/10.1038/s41567-025-02812-0

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