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arXiv 2402.07975quant-phcs.CC
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等距张量网络态的计算复杂性

Computational complexity of isometric tensor network states

University of Copenhagen(哥本哈根大学);University of Washington(华盛顿大学)

Daniel Malz, Rahul Trivedi

AI总结:

本文研究了等距张量网络态的计算复杂性,发现计算其局部期望值在弱单射下是BQP完全的,但在强单射下存在高效经典算法,并揭示了其相变特性。

摘要:

我们确定了等距张量网络态(isoTNS)的计算能力,这是一种变分拟设,最初开发用于数值寻找和计算二维中有能隙基态和拓扑态的性质。通过将2D isoTNS映射到1+1D酉量子电路,我们发现计算isoTNS中的局部期望值是$\textsf{BQP}$-完全的。然后我们引入了单射isoTNS,即作为无 frustration 哈密顿量唯一基态的isoTNS,其特征是单射参数$δ\in(0,1/D]$,其中$D$是isoTNS的键维数。我们证明单射性必然以$η=δ^2D^2$的速率向电路添加退极化噪声。我们证明弱单射isoTNS(小$δ$)仍然是$\textsf{BQP}$-完全的,但存在一种高效的经典算法来计算强单射isoTNS($η\geq0.41$)中的局部期望值。从isoTNS采样对应于监控量子动力学,我们展示了一个isoTNS家族,它经历了从困难体制到监控电路可以被高效采样的容易相的相变。我们的结果可用于设计可证明的算法来收缩isoTNS。我们将某些无 frustration 哈密顿量的基态映射到少一维的开路动力学,这可能具有独立的意义。

英文摘要:

We determine the computational power of isometric tensor network states (isoTNS), a variational ansatz originally developed to numerically find and compute properties of gapped ground states and topological states in two dimensions. By mapping 2D isoTNS to 1+1D unitary quantum circuits, we find that computing local expectation values in isoTNS is $\textsf{BQP}$-complete. We then introduce injective isoTNS, which are those isoTNS that are the unique ground states of frustration-free Hamiltonians, and which are characterized by an injectivity parameter $δ\in(0,1/D]$, where $D$ is the bond dimension of the isoTNS. We show that injectivity necessarily adds depolarizing noise to the circuit at a rate $η=δ^2D^2$. We show that weakly injective isoTNS (small $δ$) are still $\textsf{BQP}$-complete, but that there exists an efficient classical algorithm to compute local expectation values in strongly injective isoTNS ($η\geq0.41$). Sampling from isoTNS corresponds to monitored quantum dynamics and we exhibit a family of isoTNS that undergo a phase transition from a hard regime to an easy phase where the monitored circuit can be sampled efficiently. Our results can be used to design provable algorithms to contract isoTNS. Our mapping between ground states of certain frustration-free Hamiltonians to open circuit dynamics in one dimension fewer may be of independent interest.

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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