183rd RQC Seminar

  • 講演者

    Mr. Alex Chapple
    ( Département de physique, Faculté des sciences, Université de Sherbrooke )

  • 日程

    2025年1月27日（月） 13:00-14:00 （1:00 p.m. -2:00 p.m.）

  • 開催場所

    ハイブリッド（ZOOM・ Room S507 at Wako Chem. and Mat. Phys. Bldg./ 物質科学研究棟5階 S507 (S51)）

  • 講演タイトル

    Balanced cross-Kerr coupling for superconducting qubit readout

  • お問合せ

    yasunobu.nakamura[at]riken.jp

講演概要
Dispersive readout, the standard method for measuring superconducting qubits, is limited by multiphoton qubit-resonator processes arising even at moderate drive powers [1,2,3]. These processes degrade performance, causing dispersive readout to lag behind single- and two-qubit gates in both speed and fidelity. In addition, recently it has demonstrated that these deleterious multiphoton resonances occur far less often when the qubit and the resonator are coupled longitudinally [4].

Building on the insights gained from these previous studies, in this talk I will introduce a novel readout method for superconducting qubits, termed “Junction readout” [5]. Junction readout leverages the non-perturbative cross-Kerr interaction resulting from coupling a qubit and a resonator via a Josephson junction. Furthermore, by adding a capacitive coupling in parallel to the junction, Purcell decay can be suppressed without the need for a Purcell filter.

Our proposed readout method outperforms dispersive readout in both fidelity and speed, increases flexibility for resonator frequency allocation, and importantly, substantially suppresses multiphoton resonances that are detrimental to the quantum non-demolition nature of the readout. Notably, these improvements are achieved with a hardware overhead comparable to that of dispersive readout. Junction readout overcomes many of the limitations posed by dispersive readout and can be implemented readily with only small modifications to current hardware.

[1] Sank et al., PRL. 117, 190503 (2016).
[2] Khezri et al., Phys. Rev. Appl. 20, 054008 (2023).
[3] Dumas, Groleau-Paré et al., PRX. 14, 041023 (2024)
[4] Chapple et al., arXiv:2412.07734 (2024)
[5] Chapple, Benhayoune-Khadraoui et al., arXiv:2501.09010 (2025)

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