The ALPHA collaboration has for the first time observed single-photon excitation of antihydrogen atoms from the ground (1S) state to the 2P state using 121nm pulsed laser light - the so-called lyman-alpha line of the Lyman series.

The results were published in Nature on August 22nd 2018 and also demonstrate how the pulsed laser-light can be used to measure the temperature of the antihydrogen atoms. The single-photon lyman-alpha transition takes ALPHA one step closer to laser-cooling of antihydrogen, a feat that would dramatically improve the potential for more precise measurements of the also recently detailed 1S-2S transition as well as measurements of the gravitational influence on antihydrogen. The expansion of ALPHA to do the latter in ALPHA is currently underway.