抗磁通线存储的鲁棒CZ门
Robust CZ gate against flux line memory
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中文总结 AI 辅助
该研究针对传统预失真在存在磁通线存储时无法维持高保真重复CZ门的问题，将磁通线失真建模为有状态经典执行器动力学，通过优化磁通脉冲设计出鲁棒CZ门，在十门序列中大幅降低了不保真度。
中文摘要 AI 辅助
高保真CZ门是超导量子处理器的核心，但基于磁通调谐的实现仍对脉冲失真敏感。传统预失真通常用于孤立门，可恢复芯片处的期望磁通，但如果存在磁通线存储，会失效，导致重复CZ门的保真度迅速下降。为解决该问题，我们将磁通线失真建模为与量子系统耦合的有状态经典执行器的动力学。利用一阶戴森展开，我们推导了由初始磁通线状态变化引起的误差生成元。随后，我们通过优化磁通脉冲设计鲁棒CZ门，以抑制这些生成元并最小化门输出处的残余磁通线状态。单极点磁通线模型显示出预期的一阶鲁棒平台。对于更实用的三极点模型，优化后的CZ脉冲实现了平均保真度F_avg=99.998%，抑制了所有一阶误差生成元，并使残余磁通线状态接近零。在门之间无额外等待时间的情况下，我们的鲁棒脉冲在完整的十门序列中实现了平均保真度F_avg=99.97%，与相同预失真协议下的基线相比，将序列不保真度降低了约2.3×10³倍。这些结果表明，明确考虑磁通线存储可在重复门序列中维持高保真CZ操作，并解决了传统预失真的一个关键局限。
英文摘要
High-fidelity CZ gates are central to superconducting quantum processors, but implementations based on flux tuning are still sensitive to pulse distortion. Conventional predistortion, typically used for an isolated gate, can recover the desired flux at the chip but it fails if the flux line memory exists, causing the fidelity of repeated CZ gates to drop rapidly. To address this issue, we model the flux line distortion as the dynamics of a stateful classical actuator coupled to a quantum system. Using a first-order Dyson expansion, we derive the error generators induced by variations in the initial flux-line state. We then design a robust CZ gate by optimizing the flux pulse to suppress these generators and minimize the residual flux line state at the gate exit. A one-pole flux line model shows the expected first-order robustness plateau. For a more practical three-pole model, the optimized CZ pulse achieves $F_{\mathrm{avg}}=99.998\%$, suppresses all first-order error generators, and brings the residual flux line state close to zero. With no additional waiting time between gates, our robust pulse achieves $F_{\mathrm{avg}}=99.97\%$ for the complete ten-gate sequence and reduces the sequence infidelity by a factor of about $2.3\times10^{3}$ relative to the baseline under the same predistortion protocol. These results show that explicitly accounting for flux line memory maintains high-fidelity CZ operation across repeated gate sequences and addresses a key limitation of conventional predistortion.
发表机构
- International Quantum Academy（国际量子科学院）
- Shenzhen Branch Hefei National Laboratory（合肥国家实验室深圳分部）
机构由 AI 辅助整理，请以论文原文为准。
