论文标题

用于构建SPT状态和量子蜂窝自动机的非本地有限深度电路

Non-local finite-depth circuits for constructing SPT states and quantum cellular automata

论文作者

Stephen, David T., Dua, Arpit, Lavasani, Ali, Nandkishore, Rahul

论文摘要

是否可以通过从简单的产品状态开始并使用有限的深度量子电路来制备给定的目标状态,这是凝结物理物理和量子信息科学的关键问题。它基于拓扑阶段的分类以及对拓扑量子代码的理解,并且与设备实现具有明显的相关性。传统上,这个问题假设量子电路由几何局部的单一门组成。受到嘈杂的中间量子设备的出现的启发,我们用$ k $ - 本地的大门重新考虑了这个问题,即不超过$ k $的自由度的大门,但并不限制在几何上是本地的。首先,我们构建了对称$ k $ - 局部门的显式有限深度电路,这些电路从初始A产品状态中创建了对称性保护的拓扑(SPT)状态。我们的构建既适用于受到全局对称性和子系统对称性保护的SPT状态,但不适用于具有更高形式对称性的人,我们猜测这仍然是并非繁琐的。接下来,我们将展示如何使用$ K $ - 局部门的有限深度电路在任何维度上实现任意翻译不变的量子蜂窝自动机(QCA)。这些结果表明,在存在$ k $ - 局部相互作用的情况下,SPT阶段和QCA的拓扑分类都崩溃了。我们此外认为,SPT阶段对于通用$ K $ - 局部对称扰动而言是脆弱的。最后,我们通过讨论对其他阶段的含义,例如分形式阶段,并调查未来的方向。我们的分析打开了一个新的以实验动机的概念方向,研究了相位的稳定性和状态制备的可行性,而无需假设几何位置。

Whether a given target state can be prepared by starting with a simple product state and acting with a finite-depth quantum circuit is a key question in condensed matter physics and quantum information science. It underpins classifications of topological phases, as well as the understanding of topological quantum codes, and has obvious relevance for device implementations. Traditionally, this question assumes that the quantum circuit is made up of unitary gates that are geometrically local. Inspired by the advent of noisy intermediate-scale quantum devices, we reconsider this question with $k$-local gates, i.e. gates that act on no more than $k$ degrees of freedom, but are not restricted to be geometrically local. First, we construct explicit finite-depth circuits of symmetric $k$-local gates which create symmetry-protected topological (SPT) states from an initial a product state. Our construction applies both to SPT states protected by global symmetries and subsystem symmetries, but not to those with higher-form symmetries, which we conjecture remain nontrivial. Next, we show how to implement arbitrary translationally invariant quantum cellular automata (QCA) in any dimension using finite-depth circuits of $k$-local gates. These results imply that the topological classifications of SPT phases and QCA both collapse to a single trivial phase in the presence of $k$-local interactions. We furthermore argue that SPT phases are fragile to generic $k$-local symmetric perturbations. We conclude by discussing the implications for other phases, such as fracton phases, and surveying future directions. Our analysis opens a new experimentally motivated conceptual direction examining the stability of phases and the feasibility of state preparation without the assumption of geometric locality.

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