论文标题
量子轨迹的微不足道,接近有向渗滤过渡的量子
Triviality of quantum trajectories close to a directed percolation transition
论文作者
论文摘要
我们研究了由统一大门,投影测量和控制操作的量子电路,这些量子电路将系统带向纯净的吸收状态。随着这些对照操作的速率提高:测量引起的纠缠跃迁,以及向吸收状态的定向渗透过渡(在这里被视为产品状态)时,发生了两种类型的相变。在这项工作中,我们在分析上表明,这些过渡通常是不同的,在达到吸收状态过渡之前,量子轨迹变得分离,我们分析了它们的关键特性。我们引入了一类简单的模型,其中每个量子轨迹中的测量值定义了有效的张量网络(ETN) - 最初时空图的子图进行了非平凡的时间演变。通过分析ETN的纠缠特性,我们表明纠缠和吸收状态过渡仅在无限的局部希尔伯特空间维度的极限下重合。专注于Clifford模型,该模型允许用于大型系统大小的数值模拟,我们验证了我们的预测并研究了大型局部希尔伯特空间维度的两个过渡之间的有限尺寸交叉。我们提供的证据表明,纠缠过渡由与没有反馈的混合电路中相同的固定点约束。
We study quantum circuits consisting of unitary gates, projective measurements, and control operations that steer the system towards a pure absorbing state. Two types of phase transition occur as the rate of these control operations is increased: a measurement-induced entanglement transition, and a directed percolation transition into the absorbing state (taken here to be a product state). In this work we show analytically that these transitions are generically distinct, with the quantum trajectories becoming disentangled before the absorbing state transition is reached, and we analyze their critical properties. We introduce a simple class of models where the measurements in each quantum trajectory define an Effective Tensor Network (ETN) -- a subgraph of the initial spacetime graph where nontrivial time evolution takes place. By analyzing the entanglement properties of the ETN, we show that the entanglement and absorbing-state transitions coincide only in the limit of infinite local Hilbert-space dimension. Focusing on a Clifford model which allows numerical simulations for large system sizes, we verify our predictions and study the finite-size crossover between the two transitions at large local Hilbert space dimension. We give evidence that the entanglement transition is governed by the same fixed point as in hybrid circuits without feedback.