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Advances in High Energy Physics
Volume 2015 (2015), Article ID 379642, 16 pages
Review Article

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

1Laboratoire Kastler-Brossel, CNRS, ENS, Collège de France, UPMC, Campus Jussieu, 75252 Paris, France
2Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
3ETH Zurich, 8093 Zurich, Switzerland
4Institut de Recherche sur les lois Fondamentales de l’Univers, CEA Saclay, 91191 Gif-sur-Yvette, France
5Institut Max von Laue-Paul Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France
6P.N. Lebedev Physical Institute, 53 Leninsky Prospekt, 117924 Moscow, Russia

Received 29 July 2014; Accepted 1 October 2014

Academic Editor: Ignatios Antoniadis

Copyright © 2015 G. Dufour et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The publication of this article was funded by SCOAP3.


Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.