在固定频率跨导量子比特中实现具有保留计算态相干性的预示性泄漏检测
Heralded Leakage Detection with Preserved Computational-State Coherence in a Fixed-Frequency Transmon
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中文总结 AI 辅助
研究超导量子处理器计算子空间外泄漏检测问题，通过在色散读出时对计算跃迁施加拉比驱动实现预示性泄漏检测，给出检测保真度、误报率等数据，该方案无需额外电路元件，适用于多种超导量子比特。
中文摘要 AI 辅助
计算子空间外的泄漏是超导量子处理器中的主要误差机制。在不干扰编码量子信息的情况下检测泄漏可提供误差校正解码器利用的预示性误差信号。然而，标准色散读出会不加区分地使所有量子比特本征态坍缩。本文通过在色散读出期间对计算跃迁施加拉比驱动，在固定频率跨导量子比特上演示了预示性泄漏检测。该驱动使计算态对谐振器上的探测器不可区分，同时使第二及更高激发态与计算态可区分。在80纳秒检测窗口内实现了97.1(3)%的泄漏检测保真度，计算子空间的误报率为2.3(3)%。在无泄漏结果的条件下，检测后状态在计算态和泄漏态等量混合的六个基本态上平均保真度保持为92.9(5)%。该方案除标准色散读出所用元件外无需其他电路元件，无需硬件修改即可应用于各种类型的超导量子比特。
英文摘要
Leakage out of the computational subspace is a major error mechanism in superconducting quantum processors. Detecting leakage without disturbing the encoded quantum information can provide a heralded error signal that error-correction decoders exploit. However, standard dispersive readout collapses all qubit eigenstates indiscriminately. Here, we demonstrate heralded leakage detection on a fixed-frequency transmon by applying a Rabi drive on the computational transition during dispersive readout. The drive makes the computational states indistinguishable to the probe on the resonator while leaving the second and higher excited states distinguishable from the computational states. We achieve a leakage-detection fidelity of 97.1(3)% within the 80-ns detection window, with a false-flag rate of 2.3(3)% from the computational subspace. Conditioned on the no-leakage outcome, the post-detection state retains an average fidelity of 92.9(5)% across the six cardinal states for an equal mixture of computational and leakage population. The scheme requires no circuit elements beyond those used for standard dispersive readout, making it applicable to various types of superconducting qubits without hardware modification.
