We report better-than-classical success probabilities for a complete Grover quantum search algorithm on the largest scale demonstrated to date, of up to five qubits, using two different IBM platforms. This is enabled by error suppression via robust dynamical decoupling. Further improvements arise after the use of measurement error mitigation, but the latter is insufficient by itself for achieving better-than-classical performance. For two qubits, we demonstrate a 99.5% success probability via the use of the [[4, 2, 2]] quantum error-detection (QED) code. This constitutes a demonstration of quantum algorithmic breakeven via QED. Along the way, we introduce algorithmic error tomography (AET), a method that provides a holistic view of the errors accumulated throughout an entire quantum algorithm, filtered via the errors detected by the QED code used to encode the circuit. We demonstrate that AET provides a stringent test of an error model based on a combination of amplitude damping, dephasing, and depolarization.

我们报告了使用两种不同的 IBM 平台，迄今为止展示的最大规模（最多 5 个量子位）的完整 Grover 量子搜索算法的成功概率优于经典算法。这是通过稳健的动态解耦进行误差抑制来实现的。使用测量误差缓解后出现了进一步的改进，但后者本身不足以实现优于经典的性能。对于两个量子位，我们通过使用 [[4, 2, 2]] 量子错误检测 (QED) 代码证明了 99.5% 的成功概率。这证明了通过 QED 实现量子算法盈亏平衡。在此过程中，我们引入了算法错误断层扫描(AET)，这种方法可以提供整个量子算法中累积的错误的整体视图，并通过用于对电路进行编码的 QED 代码检测到的错误进行过滤。我们证明 AET 提供了基于振幅阻尼、移相和去极化组合的误差模型的严格测试。