In its standard formulation, quantum backflow is a classically impossible phenomenon in which a free quantum particle in a positive-momentum state exhibits a negative probability current. Recently, Miller et al. [Quantum 5, 379 (2021)] have put forward a new, "experiment-friendly" formulation of quantum backflow that aims at extending the notion of quantum backflow to situations in which the particle's state may have both positive and negative momenta. Here, we investigate how the experiment-friendly formulation of quantum backflow compares to the standard one when applied to a free particle in a positive-momentum state. We show that the two formulations are not always compatible. We further identify a parametric regime in which the two formulations appear to be in qualitative agreement with one another.

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关于量子回流的实验友好公式

在其标准公式中，量子回流是一种经典不可能的现象，其中处于正动量状态的自由量子粒子表现出负概率电流。最近，米勒等人。[Quantum 5, 379 (2021)] 提出了一种新的“实验友好”的量子回流公式，旨在将量子回流的概念扩展到粒子状态可能同时具有正动量和负动量的情况。在这里，我们研究了当应用于处于正动量状态的自由粒子时，实验友好的量子回流公式与标准公式相比如何。我们表明这两种公式并不总是兼容的。我们进一步确定了一种参数化机制，其中两种公式似乎彼此定性一致。