非相互作用费米子量子线路中测量诱导的纠缠跃迁：玻恩规则与强迫测量
Measurement-induced entanglement transitions in quantum circuits of non-interacting fermions: Born-rule versus forced measurements
摘要：
我们解决的纠缠跃迁在监测随机量子线路的非相互作用费米子，特别是，玻恩规则和强制测量是否产生相同的普适性类的问题。对于一个通用的电路，没有对称性以外的费米子宇称，作用于一维马约拉纳链，我们数值计算得到几个临界指数，提供了明确的证据表明，这两个过渡与玻恩规则和强制测量是在不同的普适性类。我们通过识别基本的统计力学模型为我们的数值结果提供了一个理论上的理解，该模型是从Jian等人建立的一般对应关系中得出的，物理评论B 106，134206，非相互作用费米子的非幺正电路和十重Altland-Zirnbauer（AZ）对称类之间。AZ类对于电路的Born规则和强制测量是相同的。对于所考虑的电路（AZ DIII类），描述过渡的统计力学模型是主要的手征非线性西格玛模型，其场变量是分别用于强制和Born规则测量的副本限制$n\to 0$和$n\to 1$中的${\rm SO}(n)$矩阵。前者是在一个安德森局域化普适类，而我们表明，后者是在一个新的普适类以外的安德森局域化。这两种纠缠跃迁都是由$\mathbb{Z}_2$拓扑缺陷的增殖驱动的。不同的副本限制说明了普适性类的差异。此外，我们提供了数值和基于量子力学的参数，纠缠跃迁在先前研究的监测电路的马约拉纳费米子的回路模型的基础上的交叉，一个高度精细的调谐电路，属于一个普适类不同的通用电路中的两个过渡在本文中讨论。
英文摘要：
We address entanglement transitions in monitored random quantum circuits of non-interacting fermions, in particular, the question of whether Born-rule and forced measurements yield the same universality class. For a generic circuit with no symmetry other than fermion parity, acting on a one-dimensional Majorana chain, we numerically obtain several critical exponents, providing clear evidence that the two transitions with Born-rule and forced measurements are in different universality classes. We provide a theoretical understanding for our numerical results by identifying the underlying statistical mechanics model which follows from the general correspondence, established in Jian et al., Phys. Rev. B 106, 134206, between non-unitary circuits of non-interacting fermions and the ten-fold Altland-Zirnbauer (AZ) symmetry classes. The AZ class is the same for Born-rule and forced measurements of the circuits. For the circuit under consideration (in AZ class DIII), the statistical mechanics model describing the transition is the principal chiral non-linear sigma model whose field variable is an ${\rm SO}(n)$ matrix in the replica limits $n\to 0$ and $n\to 1$ for forced and Born-rule measurements, respectively. The former is in an Anderson localization universality class while we show that the latter is in a novel universality class beyond Anderson localization. Both entanglement transitions are driven by proliferation of $\mathbb{Z}_2$ topological defects. The different replica limits account for the difference in the universality classes. Furthermore, we provide numerical and symmetry-based arguments that the entanglement transition in the previously-studied monitored circuit of Majorana fermions based on the loop model with crossings, a highly fine-tuned circuit, belongs to a universality class different from both transitions in the generic circuits discussed in this paper.
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