qFD: 針對量子機器中相干和去極化錯誤的診斷方法

Abstract

故障引起的錯誤會嚴重影響噪聲中等規模量子（NISQ）電路的正確性。在這項工作中，我們提出了一種診斷NISQ電路中相干和非相干故障的技術。所提出的技術包括三個階段：粗略診斷、精細診斷和去極化診斷。粗略診斷通過在布洛赫球上進行網格搜索來定位相干故障的大致範圍。然後，精細診斷根據縮小的搜索空間精確定位相干故障。最後，去極化診斷測量極化故障的大小。我們使用Qiskit模擬器進行了技術演示，其中包括無噪聲和有噪聲的後端。我們診斷了具有27個單量子位元、6個雙量子位元相干故障和7個注入的去極化故障的量子電路。診斷出的故障量子閘與注入的故障量子閘之間的平均量子閘保真度超過99.95％，優於相同條件下的傳統量子過程層析。還在IBMQ設備上進行了實驗，結果顯示，超過99.83％的平均量子閘保真度表明我們的技術仍然在實際量子電路設備上保持良好的分辨率。

Errors caused by faults would strongly affect the correctness of noisy intermediate-scale quantum (NISQ) circuits. In this work, we propose a technique for diagnosing coherent and incoherent faults for NISQ circuits. The proposed technique contains three phases: rough diagnosis, fine diagnosis, and depolarizing diagnosis. Rough diagnosis grid searches the Bloch sphere to locate an approximate range of a coherent fault. Fine diagnosis then precisely locates the coherent fault size based on the narrowed-down search space. At last, depolarizing diagnosis measures the depolarizing fault size. We demonstrate our technique using the Qiskit simulator with noise-free and noisy backends. The diagnosis accuracy between the diagnosed faulty gates and the injected faulty gates is over 99.95\%, which is better than traditional quantum process tomography under the same conditions. Our results show that the diagnosis error of coherent faults does not affect the diagnosis accuracy of depolarizing faults. Experiments on the IBM Q devices have also been performed, and results of over 99.83\% diagnosis accuracy show that our technique still preserves good resolution on real quantum circuit devices.