论文标题

浅阴影:使用低深度随机电路的期望估算

Shallow shadows: Expectation estimation using low-depth random Clifford circuits

论文作者

Bertoni, Christian, Haferkamp, Jonas, Hinsche, Marcel, Ioannou, Marios, Eisert, Jens, Pashayan, Hakop

论文摘要

我们提供实用和强大的方案,用于使用该州的副本副本来学习未知N Qubit量子状态的许多属性。具体而言,我们提出了一个深度调制的随机测量方案,该方案基于随机的Pauli测量和随机的Clifford测量,在两个已知的经典阴影方案之间插值。这些可以在我们的方案中分别将其视为零和无限深度的特殊情况。我们专注于深度在n中对数尺度缩放的制度,并提供了证据表明这两个极端方案的理想特性,而与随机克利福德方案相反,在实验上也可行。我们提出了两个关键任务的方法;从生成的经典阴影中估算某些可观察到的期望值,并在深度调制的阴影规范上计算上限,从而为输出估计的准确性提供了严格的保证。我们认为可以写入可以写入poly(N)Paulis和可观察到的线性组合的可观察物,可以将其写入低键尺寸矩阵产品运算符。对于以前的观测值类别,两个任务在n中有效地解决。对于后类,我们不能保证效率,而是提出一种在实践中起作用的方法。通过变异计算张量网络的预言近似近相位,然后可以使用该量子进行有效执行这两个任务。

We provide practical and powerful schemes for learning many properties of an unknown n-qubit quantum state using a sparing number of copies of the state. Specifically, we present a depth-modulated randomized measurement scheme that interpolates between two known classical shadows schemes based on random Pauli measurements and random Clifford measurements. These can be seen within our scheme as the special cases of zero and infinite depth, respectively. We focus on the regime where depth scales logarithmically in n and provide evidence that this retains the desirable properties of both extremal schemes whilst, in contrast to the random Clifford scheme, also being experimentally feasible. We present methods for two key tasks; estimating expectation values of certain observables from generated classical shadows and, computing upper bounds on the depth-modulated shadow norm, thus providing rigorous guarantees on the accuracy of the output estimates. We consider observables that can be written as a linear combination of poly(n) Paulis and observables that can be written as a low bond dimension matrix product operator. For the former class of observables both tasks are solved efficiently in n. For the latter class, we do not guarantee efficiency but present a method that works in practice; by variationally computing a heralded approximate inverses of a tensor network that can then be used for efficiently executing both these tasks.

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