  Quantum backflow is usually understood as a quantum interference phenomenon
where probability current of a quantum particle points in the opposite
direction to particle's momentum. Here, we quantify the amount of quantum
backflow for arbitrary momentum distributions, paving the way towards its
experimental verification. We give examples of backflow in gravitational and
harmonic potential, and discuss experimental procedures required for the
demonstration using atomic gravimeters. Such an experiment would show that the
probability of finding a free falling particle above initial level could grow
for suitably prepared quantum state with most momentum downwards.
