  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.
