Observation of the 1S-2S Transition in Trapped Antihydrogen

Our current understanding of physics suggests that matter and antimatter should be created and destroyed in equal amounts, but this seems inconsistent with the observation that our universe consists almost entirely of matter. Comparisons between matter and antimatter could reveal new physics which explains why the universe has formed with this apparent imbalance. The 1S-2S transition of hydrogen has been measured with incredible precision, and a similarly precise measurement of the 1S-2S transition of antihydrogen would constitute one of the best comparisons between matter and antimatter.

The ALPHA collaboration have been producing and trapping antihydrogen since 2010. This thesis presents an overview of the apparatus and techniques and examines the theoretical aspects of antihydrogen spectroscopy. Generating sufficient optical intensity at 243 nm to excite the 1S-2S transition in a reasonable amount of time requires an enhancement cavity. The development of this enhancement cavity and the setup of the ultra-stable 243 nm laser source form the main focus of this thesis.

The thesis concludes by reporting the first observation of the 1S-2S transition in trapped antihydrogen, which can be interpreted as a comparison between matter and antimatter at the 200 parts-per-trillion level. This result was aided by a significantly improved trapping rate of 10.5 ± 0.6 detected trapped antihydrogen atoms per production cycle, and the stacking of multiple production cycles without ramping down the magnetic trap to accumulate more than 70 simultaneously trapped antihydrogen atoms.

Steven Armstrong Jones, PhD Thesis, Swansea University (2017)