用不指定自旋多重性的变分量子本征求解器算法计算分析化学反应
Computational analysis of chemical reactions using a variational quantum eigensolver algorithm without specifying spin multiplicity
摘要：
沿着基态势能面结合未知自旋态的化学反应的分析是具有挑战性的，因为电子态必须使用不同的自旋多重性单独计算多次以找到最低能量状态。然而，原则上，基态可以通过使用量子计算机的单一计算而获得，而无需预先指定自旋多重性。在目前的工作中，PtCO的基态势能曲线计算作为一个概念验证使用变分量子本征求解器（VQE）算法。该系统表现出单重态-三重态交叉作为Pt和CO之间的相互作用的结果。VQE计算使用statevector模拟器被发现收敛到一个单重态的键合区域，而三重态得到的解离极限。采用误差缓解技术后，使用实际量子器件进行的计算提供了模拟能量的$\pm$ 2 kcal/mol内的势能。在成键区和解离区的自旋多重性可以清楚地区分，即使在少量的情况下射击。这项研究的结果表明，量子计算可以成为分析系统化学反应的有力工具，对于这些系统，基态的自旋多重性和该参数的变化是事先未知的。
英文摘要：
The analysis of a chemical reaction along the ground state potential energy surface in conjunction with an unknown spin state is challenging because electronic states must be separately computed several times using different spin multiplicities to find the lowest energy state. However, in principle, the ground state could be obtained with just a single calculation using a quantum computer without specifying the spin multiplicity in advance. In the present work, ground state potential energy curves for PtCO were calculated as a proof-of-concept using a variational quantum eigensolver (VQE) algorithm. This system exhibits a singlet-triplet crossover as a consequence of the interaction between Pt and CO. VQE calculations using a statevector simulator were found to converge to a singlet state in the bonding region, while a triplet state was obtained at the dissociation limit. Calculations performed using an actual quantum device provided potential energies within $\pm$2 kcal/mol of the simulated energies after adopting error mitigation techniques. The spin multiplicities in the bonding and dissociation regions could be clearly distinguished even in the case of a small number of shots. The results of this study suggest that quantum computing can be a powerful tool for the analysis of the chemical reactions of systems for which the spin multiplicity of the ground state and variations in this parameter are not known in advance.
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