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A quantum electromechanical interface for long-lived phonons



In single crystals, the suppression of intrinsic loss channels at low temperatures leads to exceptionally long mechanical lifetimes. Quantum electrical control of such long-lived mechanical oscillators would enable the development of phononic memory elements, sensors and transducers. The integration of piezoelectric materials is one approach to introducing electrical control, but the challenges of combining heterogeneous materials lead to severely limited phonon lifetimes. Here we present a non-piezoelectric silicon electromechanical system capable of operating in the gigahertz frequency band. Relying on a driving scheme based on electrostatic fields and the kinetic inductance effect in disordered superconductors, we demonstrate a parametrically enhanced electromechanical coupling of g/2π = 1.1 MHz, sufficient to enter the strong-coupling regime with a cooperativity of \({{{\mathcal{C}}}}={1,200}\). In our best devices, we measure mechanical quality factors approaching Q ≈ 107, measured at low-phonon numbers and millikelvin temperatures. Despite using strong electrostatic fields, we find the cavity mechanics system in the quantum ground state, verified by thermometry measurements. Simultaneously achieving ground-state operation, long mechanical lifetimes and strong coupling sets the stage for employing silicon electromechanical devices in hybrid quantum systems and as a tool for studying the origins of acoustic loss in the quantum regime.

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Fig. 1: Electrostatic transduction.
Fig. 2: Microwave spectrum.
Fig. 3: Mechanical lifetime measurements.
Fig. 4: Probing the limits of parametric enhancement.
Fig. 5: Demonstration of the strong-coupling regime.
Fig. 6: Interaction of the mechanical resonator with the TLS bath.

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Data availability

The datasets utilized to generate the plots in the paper are available on Zenodo ( All other data generated and/or analysed during the current study are available from the corresponding author upon reasonable request.


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We thank O. Painter and M. Kalaee for the fruitful discussions that led to the conception of this work. This work was supported by start-up funds from the EAS division at Caltech, National Science Foundation (grant no. 2137776), and a KNI-Wheatley scholarship. This material is based on work supported by the US Department of Energy Office of Science National Quantum Information Science Research Centers. C.J. acknowledges support from an IQIM/AWS Postdoctoral Fellowship.

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Authors and Affiliations



A.B. and M.M. came up with the concept and designed the experiment. A.B. and H.Z. worked on the fabrication of the devices, conducted the measurements and analysed the data. C.J. established the measurement set-up. H.G.L. and P.K.D. performed the deposition of superconducting thin films. A.B., C.J. and M.M. wrote the paper with input from all authors. M.M. supervised the project.

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Correspondence to Mohammad Mirhosseini.

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Bozkurt, A., Zhao, H., Joshi, C. et al. A quantum electromechanical interface for long-lived phonons. Nat. Phys. 19, 1326–1332 (2023).

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