论文标题
流体费米片片段，用于优化变异量子质量的电子哈密顿量的量子测量
Fluid fermionic fragments for optimizing quantum measurements of electronic Hamiltonians in the variational quantum eigensolver
论文作者
论文摘要
测量分子电子哈密顿量的预期值是变异量子本质量的具有挑战性的部分之一。一种广泛使用的策略是使用费米子操作员代数表示哈密顿量作为可测量片段的总和。这样的片段具有保存可用于缓解误差的分子对称性的优势。获得哈密顿期望值所需的测量数量与碎片差异总和成正比。在这里，我们引入了一种新方法，通过利用片段形式的灵活性来降低片段的方差。由于职业编号运算符的势力，两电子片段的某些部分可以变成单电子片段，然后可以部分收集到纯粹的单电子片段中。这种重新分配不会影响哈密顿量的期望值，而是对每个片段的差异都有不利的贡献。提出的方法通过使用使用经典有效的量子波函数估计的方差来找到最佳的回归。几个分子的数值测试表明，单电子项的重新分配降低了测量数的数量不仅仅是一个数量级。
Measuring the expectation value of the molecular electronic Hamiltonian is one of the challenging parts of the variational quantum eigensolver. A widely used strategy is to express the Hamiltonian as a sum of measurable fragments using fermionic operator algebra. Such fragments have an advantage of conserving molecular symmetries that can be used for error mitigation. The number of measurements required to obtain the Hamiltonian expectation value is proportional to a sum of fragment variances. Here, we introduce a new method for lowering the fragments' variances by exploiting flexibility in the fragments' form. Due to idempotency of the occupation number operators, some parts of two-electron fragments can be turned into one-electron fragments, which then can be partially collected in a purely one-electron fragment. This repartitioning does not affect the expectation value of the Hamiltonian but has non-vanishing contributions to the variance of each fragment. The proposed method finds the optimal repartitioning by employing variances estimated using a classically efficient proxy for the quantum wavefunction. Numerical tests on several molecules show that repartitioning of one-electron terms lowers the number of measurements by more than an order of magnitude.
