基于时空对偶性的后选择自由纠缠动力学
Postselection-free entanglement dynamics via spacetime duality
摘要：
“混合”非幺正电路（例如，涉及幺正门和量子测量）中的纠缠动力学最近已成为深入研究的对象。通过实验实现这种物理学的主要障碍是需要对随机测量结果应用\emph{postselection}，以便重复准备给定的输出状态，从而导致指数开销。我们提出了一种方法来回避这个问题，在广泛的一类非酉电路，利用\emph{spacetime duality}。该方法将非幺正演化下混合态的净化动力学映射到相关幺正电路中的特定关联函数上。这转化为可以在数字量子模拟器上直接实现的操作协议。我们讨论了不同的纠缠相位的签名，并通过数值模拟演示的例子。通过微小的修改，所提出的协议允许测量任意子系统的纯度，这可以揭示在这类混合动力学中由混合相形成的量子纠错码的性质。
英文摘要：
The dynamics of entanglement in `hybrid' non-unitary circuits (for example, involving both unitary gates and quantum measurements) has recently become an object of intense study. A major hurdle toward experimentally realizing this physics is the need to apply \emph{postselection} on random measurement outcomes in order to repeatedly prepare a given output state, resulting in an exponential overhead. We propose a method to sidestep this issue in a wide class of non-unitary circuits by taking advantage of \emph{spacetime duality}. This method maps the purification dynamics of a mixed state under non-unitary evolution onto a particular correlation function in an associated unitary circuit. This translates to an operational protocol which could be straightforwardly implemented on a digital quantum simulator. We discuss the signatures of different entanglement phases, and demonstrate examples via numerical simulations. With minor modifications, the proposed protocol allows measurement of the purity of arbitrary subsystems, which could shed light on the properties of the quantum error correcting code formed by the mixed phase in this class of hybrid dynamics.
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