Abstract
We demonstrate strong dispersive coupling between a fluxonium superconducting qubit and a 690 megahertz mechanical oscillator, extending the reach of circuit quantum acousto-dynamics (cQAD) experiments into a new range of frequencies. We have engineered a qubit-phonon coupling rate of , and achieved a dispersive interaction that exceeds the decoherence rates of both systems while the qubit and mechanics are highly nonresonant (). Leveraging this strong coupling, we perform phonon-number-resolved measurements of the mechanical resonator and investigate its dissipation and dephasing properties. Our results demonstrate the potential for fluxonium-based hybrid quantum systems, and a path for developing new quantum sensing and information processing schemes with phonons at frequencies below 700 MHz to significantly expand the toolbox of cQAD.
- Received 27 April 2023
- Revised 13 October 2023
- Accepted 20 November 2023
DOI:https://doi.org/10.1103/PRXQuantum.4.040342
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Mechanical oscillators provide compact tools for quantum science. Recent experiments have studied nonclassical states of mechanical motion by coupling a superconducting quantum circuit to piezoelectric mechanical devices, where motion generates an electrical voltage. Most of these experiments have operated at microwave frequencies of a few gigahertz, using superconducting circuits called transmons that resemble resonators. Coupling between transmons and mechanical devices tends to weaken at lower frequencies. We demonstrate coupling to a mechanical oscillator at a lower frequency than previous experiments using a circuit called fluxonium.
Fluxonium circuits host a quantum bit (qubit), represented as a current flowing either clockwise or counterclockwise in a superconducting ring. This style of qubit is suitable for low frequencies but is challenging to integrate with mechanical systems. In our device we achieve strong coupling between qubit and mechanics while maintaining coherence of the qubit long enough to observe the quantized energy levels of the mechanics. These results enable us to access the quantum regime of mechanical motion in a new regime of frequencies and pave the way for using new types of circuits in hybrid physical systems.
Even stronger coupling to mechanics may be possible using fluxoniumlike qubits. The next steps to develop this platform include improving qubit coherence and developing a cooling protocol to simultaneously initialize the qubit and the mechanics.
