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arXiv 2207.03063quant-ph
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对称破缺减慢了ADAPT变分量子本征求解器的收敛速度

Symmetry breaking slows convergence of the ADAPT Variational Quantum Eigensolver

Luke W. Bertels, Harper R. Grimsley, Sophia E. Economou, Edwin Barnes, Nicholas J. Mayhall

摘要:

由于分子系统的量子模拟有望为表现出强电子相关性的系统提供比经典计算方法更强的优势,因此评估强相关系统的VQE性能至关重要。对于经典模拟,强相关性通常会导致哈特里-福克参考的对称性破缺,从而导致洛丁著名的“对称性困境”,即可以通过打破自旋或空间对称性来提高能量的准确性。在这里,我们探索的ADAPT-VQE使用两个强相关的系统的性能上的对称性破缺的影响:(i)“费米子化”各向异性海森堡模型,其中各向异性参数控制系统中的相关性,和(ii)压缩拉伸线性\ce{H4},其中相关性随着增加的H-H分离。在这两种情况下,增加系统的相关性水平导致平均场解的自发对称性破缺(分别为宇称和$\hat{S}^{2}$)。我们分析了参考态的对称性破缺和费米子哈密顿算符的轨道映射对ADAPT-VQE的紧致性和性能的影响。我们观察到,通过破坏对称性来提高参考态的能量,通过增加能量收敛所需的附加长度和加剧"梯度槽”问题,对ADAPT-VQE产生了有害影响。

英文摘要:

Because quantum simulation of molecular systems is expected to provide the strongest advantage over classical computing methods for systems exhibiting strong electron correlation, it is critical that the performance of VQEs be assessed for strongly correlated systems. For classical simulation, strong correlation often results in symmetry-breaking of the Hartree-Fock reference, leading to Löwdin's well-known ``symmetry dilemma'' whereby accuracy in the energy can be increased by breaking spin or spatial symmetries. Here, we explore the impact of symmetry breaking on the performance of ADAPT-VQE using two strongly correlated systems: (i) the ``fermionized" anisotropic Heisenberg model, where the anisotropy parameter controls the correlation in the system, and (ii) symmetrically-stretched linear \ce{H4}, where correlation increases with increasing H-H separation. In both of these cases, increasing the level of correlation of the system leads to spontaneous symmetry breaking (parity and $\hat{S}^{2}$, respectively) of the mean-field solutions. We analyze the role that symmetry breaking in the reference states and orbital mappings of the fermionic Hamiltonians have on the compactness and performance of ADAPT-VQE. We observe that improving the energy of the reference states by breaking symmetry has a deleterious effect on ADAPT-VQE by increasing the length of the ansatz necessary for energy convergence and exacerbating the problem of ``gradient troughs".

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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