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Millimeter Wave Readout of a Superconducting Qubit

Akash V. Dixit1,*,†, Zachary L. Parrott1,2, Dennis Chunikhin1,‡, Trevyn F. Q. Larson1,2,§, Bradley D. Hauer3, and John D. Teufel1,║

  • *Contact author: avdixit@berkeley.edu
  • †Present address: Lawrence Berkeley Laboratory, Berkeley, California 94720, USA.
  • ‡Present address: University of Maryland, College Park, Maryland 20742, USA.
  • §Present address: Google Quantum AI, Goleta, California 93111, USA.
  • ║Present address: AWS Center of Quantum Computing, Pasadena, California 91106, USA.
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Phys. Rev. Lett. 137, 180803 – Published 30 October, 2026

DOI: https://doi.org/10.1103/c84y-ggqs

Abstract

Millimeter waves are emerging as an enabling technology for connecting and enhancing different quantum platforms such as Rydberg atoms, optomechanics, and superconducting qubits. In this Letter, we explore the interaction between millimeter wave photons and conventional transmon qubits, specifically for qubit readout. We study a circuit quantum electrodynamic system consisting of a millimeter wave cavity at ωr=2π×34.7  GHz and a transmon qubit at ωq=2π×3.1  GHz coupled at rate g=2π×1.3  GHz. With such a large detuning between cavity and qubit, ωr/ωq>10, we are able to suppress drive induced unwanted resonant state transitions, enabling strong drives for qubit readout. We measure no resonant state transitions even when driving with more than 100 photons and read out the qubit state with more than 100 photons to achieve a measurement fidelity greater than 99% without the aid of a quantum limited amplifier.

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synopsis

Talking to Superconducting Qubits with Millimeter Waves

Published 30 October, 2026

A new device uses millimeter-wave radiation to accurately read the states of superconducting qubits without altering them.

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Outline

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Phys. Rev. Lett. 137, 180803– Published 30 October, 2026
  • Received 12 April 2026
  • Revised 21 July 2026
  • Accepted 3 September 2026
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