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A cryogenic electro-optic interconnect for superconducting devices


A major challenge to the scalability of cryogenic computing platforms is the heat load associated with the growing number of electrical cable connections between the superconducting circuitry and the room-temperature environment. Compared with electrical cables, optical fibres have significantly lower thermal conductivity and are widely used in modern telecommunications. However, optical modulation at cryogenic temperatures remains relatively unexplored. Here we report the cryogenic electro-optical readout of a superconducting electromechanical circuit using a commercial titanium-doped lithium niobate modulator. We demonstrate coherent spectroscopy by measuring optomechanically induced transparency and incoherent thermometry by encoding the mechanical sidebands in an optical signal. We also show that our modulators can maintain their room-temperature Pockels coefficient at 800 mK. Further optimization of the modulator design—for example, by using longer waveguides and materials with a higher Pockels coefficient—could reduce the added noise of our setup to similar levels as current semiconductor microwave amplifiers.

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Fig. 1: Principle of a cryogenic electro-optical interconnect for readout of superconducting devices.
Fig. 2: Cryogenic characterization of an LiNbO3 PM.
Fig. 3: Electro-optic readout of a coherent microwave spectrum of a superconducting electromechanical system.
Fig. 4: Electro-optic readout of an incoherent microwave spectrum of a superconducting electromechanical system.

Data availability

The data used to produce the plots within this paper are available on Zenodo ( All other data used in this study are available from the corresponding author on reasonable request.

Code availability

The code used to produce the plots within this paper is available on Zenodo (


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We thank N. J. Engelsen for thorough reading of the manuscript. This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 732894 (FET Proactive HOT), and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 835329). This work was supported by funding from the Swiss National Science Foundation under grant agreement NCCR-QSIT:51NF40_185902 and Sinergia grant no. 186364 (QuantEOM). The circuit electromechanical device was fabricated in the Center of MicroNanoTechnology (CMi) at EPFL.

Author information




T.J.K. conceived the experiment. A.Y. and I.S. performed the measurements, with contributions from Y.J.J., N.R.B., A.L., P.U. and L.Q. A.Y. and Y.J.J. analysed the data with contributions from N.R.B. A.Y. fabricated the superconducting electromechanical sample. A.Y., I.S. and T.J.K. wrote the manuscript. T.J.K. initiated and supervised the project.

Corresponding author

Correspondence to Tobias J. Kippenberg.

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Peer review informationNature Electronics thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Illustration of the gain characterization procedure.

a, Propagation of the DUT signal through the system. b, Power spectral density of the HEMT output. c, Power spectral density of the optical heterodyne detector.

Extended Data Fig. 2 Schematic signal flow when pre-amplifier is used.

Pre-amplifier gain, GPA ~102, and transduction gain, G. The equivalent added noise referred to the input after the second amplification stage is ~(GPAG)−1.

Extended Data Fig. 3 Heat dissipation and temperature gradients.

a, Relative temperature difference between PM box and heat exchanger, on 800 mK flange during a cooldown. The gray datapoints correspond to specific periods of pulse precooling and mixture condensation, where the temperature is unstable. b, Measurement of heating due to optical dissipation when the phase modulator is mounted on the 800 mK flange. c, Measurement of heating using a calibrated resistive heater mounted on the 800 mK flange.

Extended Data Fig. 4 HEMT noise characterization.

a, Experimental setup and schematic signal flow. A noise source thermalized at temperature T feeds the HEMT with Johnson noise. The measured power spectral density is proportional to the noise from the source plus the HEMT added noise. The noise source is a thermally isolated copper block containing a cryogenic resistive heater, a thermometer, and a 50Ω load. The noise source is connected to a 12 GHz low-pass filter. b, The added noise of the HEMT versus frequency. Inset: An example of the measured power spectral density at 6 GHz vs. T. The dashed line is to a fit Eq. (11).

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Youssefi, A., Shomroni, I., Joshi, Y.J. et al. A cryogenic electro-optic interconnect for superconducting devices. Nat Electron 4, 326–332 (2021).

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