@article {Baker:2021us,
	title = {Laser cooling of antihydrogen atoms},
	journal = {Nature},
	volume = {592},
	number = {7852},
	year = {2021},
	pages = {35{\textendash}42},
	abstract = {The photon{\textendash}-the quantum excitation of the electromagnetic field{\textendash}-is massless but carries momentum. A photon can therefore exert a force on an object upon collision1. Slowing the translational motion of atoms and ions by application of such a force2,3, known as laser cooling, was first demonstrated 40 years ago4,5. It revolutionized atomic physics over the following decades6{\textendash}8, and it is now a workhorse in many fields, including studies on quantum degenerate gases, quantum information, atomic clocks and tests of fundamental physics. However, this technique has not yet been applied to antimatter. Here we demonstrate laser cooling of antihydrogen9, the antimatter atom consisting of an antiproton and a positron. By exciting the 1S{\textendash}2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-αlaser radiation10,11, we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions. We observe a reduction in the median transverse energy by more than an order of magnitude{\textendash}-with a substantial fraction of the anti-atoms attaining submicroelectronvolt transverse kinetic energies. We also report the observation of the laser-driven 1S{\textendash}2S transition in samples of laser-cooled antihydrogen atoms. The observed spectral line is approximately four times narrower than that obtained without laser cooling. The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic11{\textendash}13 and gravitational14 studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.},
	isbn = {1476-4687},
	doi = {10.1038/s41586-021-03289-6},
	url = {https://doi.org/10.1038/s41586-021-03289-6},
	author = {Baker, C. J. and Bertsche, W. and Capra, A. and Carruth, C. and Cesar, C. L. and Charlton, M. and Christensen, A. and Collister, R. and Mathad, A. Cridland and Eriksson, S. and Evans, A. and Evetts, N. and Fajans, J. and Friesen, T. and Fujiwara, M. C. and Gill, D. R. and Grandemange, P. and Granum, P. and Hangst, J. S. and Hardy, W. N. and Hayden, M. E. and Hodgkinson, D. and Hunter, E. and Isaac, C. A. and Johnson, M. A. and Jones, J. M. and Jones, S. A. and Jonsell, S. and Khramov, A. and Knapp, P. and Kurchaninov, L. and Madsen, N. and Maxwell, D. and McKenna, J. T. K. and Menary, S. and Michan, J. M. and Momose, T. and Mullan, P. S. and Munich, J. J. and Olchanski, K. and Olin, A. and Peszka, J. and Powell, 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 Starko, D. M. and So, C. and Stutter, G. and Tharp, T. D. and Thibeault, A. and Thompson, R. I. and van der Werf, D. P. and Wurtele, J. S.}
}
