Abstract
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.
Highlights
A wave function of a quantum particle has physically observable characteristics that can be local or global
Already at this level of generality, it is clear that the probability current and the momentum of a quantum particle may behave very differently
Quantum backflow (QB) is an interference effect that arises from this observation
Summary
A wave function of a quantum particle has physically observable characteristics that can be local or global. The probability of finding the particle in a specific region of space or the probability current are examples of local characteristics, which can be determined given access to only small part of the wave function. The momentum is a property of the entire wave function, e.g. requires the determination of the de Broglie wavelength. Already at this level of generality, it is clear that the probability current and the momentum of a quantum particle may behave very differently. The present study, focuses on quantum backflow of individual non-relativistic quantum particles. We comment on possible experimental verification of QB using atomic gravimeters
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