Measurement Induced State Transitions and Quantum Non-Demolition Readout in Fluxonium Qubits

ORAL

Abstract

In circuit quantum electrodynamics, the projective nature of measurements relies on the validity of the dispersive approximation between a qubit and its resonator. In practice, this approximation frequently breaks down, inducing unwanted transitions that compromise the quantum non-demolition (QND) nature of the measurement [1,2,3]. Depending on parameter regime, we find that these arise even at low powers in strongly anharmonic systems such as the fluxonium.

In this work, we investigate multi-photon absorption to non-computational states intrinsic to the fluxonium Hamiltonian, finding good agreement between Floquet-based simulations and experimental data. We further examine other proposed transition mechanisms, including fluxonium array modes [4] and inelastic scattering processes [5], and assess their impact on measurement. These results provide new insights into the limits of dispersive readout in fluxonium qubits and point to design strategies that enable robust QND measurement.

[1] D. Sank, et al., PRL, 2016

[2] M. Khezri, et al., PRA, 2023

[3] M. F. Dumas, et al., PRX, 2024

[4] S. Singh, et al., PRX Quantum, 2025

[5] T. Connolly, et al., arXiv:2506.05306, 2025

*This research was sponsored in part by IARPA and the Army Research Office, under the Entangled Logical Qubits program, and was accomplished under Cooperative Agreement Number W911NF-23-2-0212; in part by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Quantum Systems Accelerator; and in part under Air Force Contract No. FA8702-15-D-0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of IARPA, the Army Research Office, or the U.S. Government.

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Presenters

  • Miguel S Moreira

    • Massachusetts Institute of Technology

Authors

  • Miguel S Moreira

    • Massachusetts Institute of Technology

  • Jorge F Marques

    • Massachusetts Institute of Technology

  • Alex Arimoto Chapple

    • Universite de Sherbrooke

  • Othmane Benhayoune Khadraoui

    • Université de Sherbrooke
    • Universite de Sherbrooke

  • Boris Varbanov

    • University of Sherbrooke
    • Université de Sherbrooke
    • Universite de Sherbrooke

  • Alexander McDonald

    • Université de Sherbrooke
    • Universite de Sherbrooke

  • Max Hays

    • Massachusetts Institute of Technology

  • Konstantin Nesterov

    • Atlantic Quantum

  • Jeffrey M Knecht

    • MIT Lincoln Laboratory

  • Bethany M Niedzielski

    • MIT Lincoln Laboratory

  • Hannah M Stickler

    • MIT Lincoln Laboratory

  • Mollie E. Schwartz

    • MIT Lincoln Laboratory

  • Alexandre Blais

    • Université de Sherbrooke
    • University of Sherbrooke
    • Universite de Sherbrooke
    • Institut Quantique, Département de Physique, Université de Sherbrooke

  • Kyle Serniak

    • MIT Lincoln Laboratory

  • Jeffrey A Grover

    • Massachusetts Institute of Technology

  • William D Oliver

    • Massachusetts Institute of Technology