Abstract

Antimatter continues to intrigue scientists due to its apparent absence in the universe. In recent years, antimatter has come under unprecedented experimental scrutiny, as we can now test the fundamental symmetries of Nature to high precision using this unique tool. We have recently become able to study atoms of antihydrogen – the antimatter equivalent of hydrogen. The question to be addressed is fundamental and profound: “Do matter and antimatter obey the same laws of physics?” The so-called Standard Model of fundamental particles and interactions requires that hydrogen and antihydrogen have the same spectrum. I will discuss the latest exciting developments in antihydrogen physics: observation of the first laser-driven transition (1S-2S) in trapped antihydrogen [1,2] observation of the antihydrogen hyperfine structure [3], and observation of the Lyman-alpha transition [4]. Precise measurement of the frequency of the 1S-2S transition could well be described as the ‘holy grail’ of physics with anti-atoms. To study antihydrogen, it must first be produced, then trapped [5], and then held for long enough [6] to observe a transition – using very few anti-atoms. I will discuss the techniques necessary to achieve the latest milestones, and then consider the future of optical and microwave spectroscopy, as well as gravitational studies [7], with antihydrogen.

1. Observation of the 1s-2s Transition in Trapped Antihydrogen, M Ahmadi et al., (ALPHA Collaboration) Nature 541, 506–510 (2017).

2 Characterization of the 1S-2S transition in antihydrogen, M Ahmadi et al., (ALPHA Collaboration), Nature 557, 71–75 (2018).

3, Observation of the hyperfine spectrum of antihydrogen, M Ahmadi et al., (ALPHA Collaboration) Nature 548, 66–69 (2017).

4. Observation of the 1S–2P Lyman-α transition in antihydrogen, M Ahmadi et al., (ALPHA Collaboration), Nature 561, 211–215 (2018).

5. Andresen, G.B. et al., Trapped Antihydrogen, Nature, 468, 673 (2010).

6. Andresen, G. B. et al. Confinement of antihydrogen for 1,000 seconds. Nature Physics 7, 558 (2011).

7. Amole, C. et al., Description and first application of a new technique to measure the gravitational mass of antihydrogen, Nature Communications DOI : 10.1038/ncomms2787 (2013).