Quantum-system characterization techniques represent the front line in the identification and mitigation of noise in quantum computing but can be expensive in terms of quantum resources and time to repeatedly employ. Another challenging aspect is that the parameters governing the performance of various operations tend to drift over time and monitoring these is hence a difficult task. One of the most promising characterization techniques, gate-set tomography (GST), provides a self-consistent estimate of the completely positive trace-preserving (CPTP) maps for a complete set of gates, as well as preparation and measurement operators. We develop a method for performance optimization seeded by tomography (POST), which couples the power of GST with a classical optimization routine to achieve a consistent gate improvement in just a short number of steps within a given calibration cycle. By construction, the POST procedure finds the best available gate operation given the hardware and is therefore robust to the effects of drift. Further, in comparison to other quantum error-mitigation techniques, it builds upon a one-time application of GST. To demonstrate the performance of this method on a real quantum computer, we map out the operations of six qubit pairs on the superconducting ibmq_poughkeepsie quantum device. Under the restriction of logical-only control, we monitor the performance of the POST approach on a chosen controlled-not (cnot) gate over a period of six weeks. In this time, we achieve a consistent improvement in gate fidelity, averaging a fidelity increase of 21.1% as measured by randomized benchmarking. The POST approach should find wide applicability as it is hardware agnostic and can be applied at the upper logical level or at a deeper pulse-control level.

中文翻译：

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改进两个Qubit闸门的稳健保真性能

量子系统表征技术代表了量子计算中噪声的识别和缓解的前沿，但在量子资源和重复使用时间方面可能会很昂贵。另一个具有挑战性的方面是，控制各种操作的性能的参数会随时间推移而漂移，因此监视这些参数是一项艰巨的任务。门控断层扫描（GST）是最有前途的表征技术之一，它为整套门以及准备和测量操作员提供了完全正迹线保留（CPTP）图的自洽估计。我们开发了一种通过层析成像（POST）进行性能优化的方法，它结合了GST的功能和经典的优化例程，以在给定的校准周期内仅需很短的几个步骤就可以实现一致的门控改进。通过构造，POST过程会在给定硬件的情况下找到最佳的可用门操作，因此对漂移的影响很稳定。此外，与其他量子误差缓解技术相比，它基于GST的一次性应用。为了演示此方法在真实量子计算机上的性能，我们在超导上绘制了六个量子位对的操作图 它基于GST的一次性应用程序。为了演示此方法在真实量子计算机上的性能，我们在超导上绘制了六个量子位对的操作图 它基于GST的一次性应用程序。为了演示此方法在真实量子计算机上的性能，我们在超导上绘制了六个量子位对的操作图ibmq_poughkeepsie量子设备。下逻辑只控制的限制，我们监测所选择的受控的POST方法的性能不（CNOT历时六周）栅极。在这次，我们实现了门保真度的持续改善，通过随机基准测试测得的保真度平均提高了21.1％。POST方法应具有广泛的适用性，因为它与硬件无关，可以在较高的逻辑级别或更深的脉冲控制级别应用。