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

TL;DR

This paper reports on a precise measurement of the position-space wave functions of gravitationally bound ultracold neutrons, confirming quantum mechanical predictions and discussing experimental and theoretical issues involved.

Contribution

It presents the first detailed measurement of neutron wave functions in gravitational bound states, advancing experimental techniques and analysis methods.

Findings

Quantum modulation of neutron states agrees with quantum mechanics

Analysis of neutron loss models improves understanding of experimental data

Discussion of phase space quantum mechanics enhances theoretical framework

Abstract

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.