Status and plans of the Gravitational Behaviour of Antihydrogen at Rest experiment

TL;DR

The GBAR experiment aims to test the Weak Equivalence Principle for antihydrogen by measuring its free fall with increasing precision, and also plans to measure the Lamb shift to determine the antiproton charge radius.

Contribution

This paper presents the current status and future plans of the GBAR experiment to measure gravitational acceleration and quantum effects of antihydrogen.

Findings

Preliminary measurements of antihydrogen free fall.

Development of quantum interference detection techniques.

Plans to measure the Lamb shift for antiproton charge radius.

Abstract

The GBAR experiment aims to directly test the Weak Equivalence Principle of ultracold antihydrogen in Earth's gravitational field. The gravitational acceleration $\bar{g}$ will be measured to a precision of $1\,\%$ using a classical free fall of the anti-atoms from a fixed height. Reaching a precision of $10^{-6}$ is planned by performing a "quantum free fall" experiment by detecting quantum interference of $\mathrm{\bar{H}}$ due to quantum gravitational bound states above a reflecting surface. Additionally, a $\mathrm{\bar{H}}$ Lamb shift measurement is being prepared in parallel that will allow to determine the antiproton charge radius at the level of $10\,\%$.