Antihydrogen is the simplest pure antimatter atomic system, and it allows for direct tests of CPT symmetry as well as the weak equivalence principle. Furthermore, the study of antihydrogen may provide clues to the matter- antimatter asymmetry observed in the universe - one of the major unanswered questions in modern physics. Since 2010, it has been possible to perform such tests on magnetically trapped antihydrogen, and this work reports on several recent studies.

Analysing the temporal and spatial distribution of annihilations as antihy- drogen atoms are released from the magnetic trap, we set limits on the gravitational acceleration of antihydrogen, ruling out a gravitational mass, Mg greater than 110 times the inertial mass, M, as well as Mg < −65M.

An improved limit on the charge neutrality of the antihydrogen atom is also presented. Stochastic electric potentials are used to empty the trap of any putatively charged antihydrogen atoms. From the lack of response to these potentials, we can set a limit for the charge of antihydrogen at |Q| < 7.1 × 10−10 e. From this measurement, the limit on the positron charge anomaly can also be improved.

As the main focus of this work, we consider the measurement of the 1S-2S transition frequency in antihydrogen. The necessary theoretical framework for an initial measurement is developed and used to identify a feasible detection method for the excited 2S atoms. Recorded data from a series of trials is then analysed by comparison to a detailed simulation of the experiment. While the two are in excellent agreement, the data collected is not compellingly different from a pure background sample. 

Chris Ørum Rasmussen