总时长低于100纳秒的低泄露超导量子比特测量
Low-leakage superconducting-qubit measurement with sub-100-ns total duration
浏览论文内容
中文总结 AI 辅助
本研究实现了总时长97(1)ns的超导transmon量子比特低泄露测量，通过大谐振器衰减率与近最优单光子信噪比的色散位移，获得高保真低泄露性能，为量子纠错提供关键技术支持。
中文摘要 AI 辅助
快速、准确且低泄露的量子比特测量是量子纠错的关键要求。在此，我们展示了对超导transmon量子比特的测量，其总时长为97(1)纳秒，该时长定义为从测量脉冲开始到后续π脉冲操作上测量诱导误差降至10⁻⁴以下的时间。通过将大的态平均谐振器衰减率κ_eff/2π=30.8 MHz与接近最优单光子信噪比条件的色散位移相结合，我们使用58纳秒的测量脉冲实现了0.17(1)%的分配误差，残留的读出光子在数十纳秒内被动耗尽，无需主动耗尽脉冲。结合重复测量序列与泄露敏感测量，我们对测量诱导的态跃迁进行了基准测试，发现每次测量的泄露率为2.7(2)×10⁻⁵，仅为背景率的两倍，且比主导分配误差的测量诱导弛豫率低两个数量级。Floquet模拟表明，工作点处存在的多光子共振耦合较弱，且以 diabatic 方式穿过，不会引发泄露。这些结果证明，大的谐振器衰减率与接近最优单光子信噪比条件的色散位移相结合，可在量子比特-谐振器失谐较小时实现快速、高保真、低泄露的色散读出。
英文摘要
Fast, accurate, and low-leakage qubit measurement is a key requirement for quantum error correction. Here, we demonstrate measurement of a superconducting transmon qubit with a total duration of 97(1) ns, defined as the time from the start of the measurement pulse until the measurement-induced error on a subsequent $π$-pulse operation falls below $10^{-4}$. By combining a large state-averaged resonator decay rate of $κ_\mathrm{eff}/2π$ = 30.8 MHz with a dispersive shift close to the optimal SNR-per-photon condition, we achieve an assignment error of 0.17(1)% using a 58-ns measurement pulse, with residual readout photons depleting passively in tens of nanoseconds without an active depletion pulse. Using a repeated-measurement sequence together with a leakage-sensitive measurement, we benchmark the measurement-induced state transitions, finding a per-measurement leakage rate of $2.7(2) \times 10^{-5}$, only twice the background rate and two orders of magnitude below the measurement-induced relaxation rate, which dominates the assignment error. Floquet simulations indicate that the multiphoton resonances present at the operating point are weakly coupled and traversed diabatically, without causing leakage. These results demonstrate that a large resonator decay rate, combined with a dispersive shift close to the optimal SNR-per-photon condition, can enable fast, high-fidelity, low-leakage dispersive readout at small qubit-resonator detuning.
