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Advances in High Energy Physics
Volume 2014 (2014), Article ID 859241, 7 pages
Review Article

Precision Measurement of the Position-Space Wave Functions of Gravitationally Bound Ultracold Neutrons

1Department of Physics, Graduate School of Science, and International Center for Elementary Particle Physics, The University of Tokyo, Tokyo 113-0033, Japan
2Department of Physics, Nagoya University, Nagoya 464-8601, Japan

Received 12 June 2014; Accepted 26 August 2014; Published 10 September 2014

Academic Editor: Valery V. Nesvizhevsky

Copyright © 2014 Y. Kamiya 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.


Gravity is the most familiar force at our natural length scale. However, it is still exotic from the view point of particle physics. The first experimental study of quantum effects under gravity was performed using a cold neutron beam in 1975. Following this, an investigation of gravitationally bound quantum states using ultracold neutrons was started in 2002. This quantum bound system is now well understood, and one can use it as a tunable tool to probe gravity. In this paper, we review a recent measurement of position-space wave functions of such gravitationally bound states and discuss issues related to this analysis, such as neutron loss models in a thin neutron guide, the formulation of phase space quantum mechanics, and UCN position sensitive detectors. The quantum modulation of neutron bound states measured in this experiment shows good agreement with the prediction from quantum mechanics.