Metcalf Mekena, Bauman Nicholas P, Kowalski Karol, de Jong Wibe A
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, California 94720, United States.
Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
J Chem Theory Comput. 2020 Oct 13;16(10):6165-6175. doi: 10.1021/acs.jctc.0c00421. Epub 2020 Sep 27.
Applications of quantum simulation algorithms to obtain electronic energies of molecules on noisy intermediate-scale quantum (NISQ) devices require careful consideration of resources describing the complex electron correlation effects. In modeling second-quantized problems, the biggest challenge confronted is that the number of qubits scales linearly with the size of the molecular basis. This poses a significant limitation on the size of the basis sets and the number of correlated electrons included in quantum simulations of chemical processes. To address this issue and enable more realistic simulations on NISQ computers, we employ the double unitary coupled-cluster (DUCC) method to effectively downfold correlation effects into the reduced-size orbital space, commonly referred to as the active space. Using downfolding techniques, we demonstrate that properly constructed effective Hamiltonians can capture the effect of the whole orbital space in small-size active spaces. Combining the downfolding preprocessing technique with the variational quantum eigensolver, we solve for the ground-state energy of H, Li, and BeH in the cc-pVTZ basis using the DUCC-reduced active spaces. We compare these results to full configuration-interaction and high-level coupled-cluster reference calculations.
在有噪声的中等规模量子（NISQ）设备上应用量子模拟算法来获取分子的电子能量，需要仔细考虑描述复杂电子关联效应的资源。在对二次量子化问题进行建模时，面临的最大挑战是量子比特的数量与分子基组的大小呈线性关系。这对基组的大小以及化学过程量子模拟中包含的相关电子数量构成了重大限制。为了解决这个问题并在NISQ计算机上实现更逼真的模拟，我们采用双酉耦合簇（DUCC）方法，将关联效应有效地降维到缩小尺寸的轨道空间，通常称为活性空间。使用降维技术，我们证明了正确构建的有效哈密顿量可以在小尺寸活性空间中捕捉整个轨道空间的效应。将降维预处理技术与变分量子本征求解器相结合，我们使用DUCC降维活性空间在cc-pVTZ基组中求解H、Li和BeH的基态能量。我们将这些结果与全组态相互作用和高级耦合簇参考计算结果进行比较。
