Magnetically trapped antihydrogen atoms can be cooled by expanding the volume of the trap in which they are confined. We report a proof-of-principle experiment in which antiatoms are deliberately released from expanded and static traps. Antiatoms escape at an average trap depth of 0 . 0 8 ± 0 . 0 1 K (statistical errors only) from the expanded trap while they escape at average depths of 0 . 2 2 ± 0 . 0 1 and 0 . 1 7 ± 0 . 0 1 K from two different static traps. (We employ temperature-equivalent energy units.) Detailed simulations qualitatively agree with the escape times measured in the experiment and show a decrease of 3 8 % (statistical error < 0 . 2 % ) in the mean energy of the population after the trap expansion without significantly increasing antiatom loss compared to typical static confinement protocols. This change is bracketed by the predictions of one-dimensional and three-dimensional semianalytic adiabatic expansion models. These experimental, simulational, and model results are consistent with obtaining an adiabatically cooled population of antihydrogen atoms that partially exchanged energy between axial and transverse degrees of freedom during the trap expansion. This result is important for future antihydrogen gravitational experiments which rely on adiabatic cooling, and it will enable antihydrogen cooling beyond the fundamental limits of laser cooling.

Ahmadi, M. and Alves, B. X. R. and Baker, C. J. and Bertsche, W. and Capra, A. and Cohen, S. and Torkzaban, C. and Cesar, C. L. and Charlton, M. and Collister, R. and Eriksson, S. and Evans, A. and Evetts, N. and Fajans, J. and Friesen, T. and Fujiwara, M. C. and Granum, P. and Hangst, J. S. and Hayden, M. E. and Hodgkinson, D. and Isaac, C. A. and Johnson, M. A. and Jones, S. A. and Jonsell, S. and Kalem, N. and Madsen, N. and Maxwell, D. and McKenna, J. T. K. and Menary, S. and Momose, T. and Munich, J. and Olchanski, K. and Olin, A. and Pusa, P. and Rasmussen, C. \O{}. and Robicheaux, F. and Sacramento, R. L. and Sameed, M. and Sarid, E. and Silveira, D. M. and So, C. and Stutter, G. and Tharp, T. D. and Thompson, R. I. and van der Werf, D. P. and Wurtele, J. S.