The antimatter equivalent of atomic hydrogen—antihydrogen—is an outstanding testbed for precision studies of matter–antimatter symmetry. Here we report on the simultaneous observation of both accessible hyperfine components of the 1S–2S transition in trapped antihydrogen. We determine the 2S hyperfine splitting in antihydrogen and—by comparing our results with those obtained in hydrogen—constrain the charge–parity–time-reversal symmetry-violating coefficients in the standard model extension framework. Our experimental protocol allows the characterization of the relevant spectral lines in 1 day, representing a 70-fold improvement in the data-taking rate. We show that the spectroscopy is applicable to laser-cooled antihydrogen with important implications for future tests of fundamental symmetries.

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 Cridland Mathad, A. 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 Kurchaninov, L. and Madsen, N. and Maxwell, D. and McKenna, J. T. K. and Menary, S. 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. Ø. 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. and Shore, G. M.