# Experiment-friendly formulation of quantum backflow

Marek Miller1,2, Woo Chee Yuan1, Rainer Dumke1,3, and Tomasz Paterek1,4,5

1School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore
2Centre of New Technologies, University of Warsaw, Poland
3Centre for Quantum Technologies, National University of Singapore, Singapore
4MajuLab, International Joint Research Unit UMI 3654, CNRS, Universite Cote d'Azur, Sorbonne Universite, National University of Singapore, Nanyang Technological University, Singapore
5Institute of Theoretical Physics and Astrophysics, Faculty of Mathematics, Physics and Informatics, University of Gdańsk, Poland

### 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.

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