Probing Trapped Antihydrogen: In Situ Diagnostics and Observations of Quantum Transitions

Antihydrogen, the bound state of a positron and an antiproton, is the simplest pure anti-atomic system and an excellent candidate to test the symmetry between matter and antimatter. This thesis focuses on the magnetic confinement of antihydrogen and the first ever resonant interaction with trapped antihydrogen, as performed by the ALPHA collaboration. The ALPHA apparatus and the techniques that have been developed to form, trap, probe, and detect antihydrogen atoms will be described in detail. The first successful demonstration of trapped antihydrogen will then be described. In the initial demonstrations, 38 trapped antihydrogen atoms were detected after being confined for at least 172 ms. Since then, over 400 antihydrogen atoms have been trapped and confinement times of 1000 s (over 15 minutes) have been demonstrated. Spectroscopy of these trapped antihydrogen atoms is the next major step forward. As an initial proof-of-principle demonstration, ALPHA induced and observed resonant positron spin flip (PSR) transitions between the ground states of antihydrogen. Because of the strong magnetic field dependence of these transition frequencies, the success of this experiment relied heavily on the ability to measure the magnetic field seen by the antihydrogen atoms. A novel method to measure the magnetic field in situ by detecting the cyclotron resonance of a trapped electron plasma is presented. This method allowed ALPHA to measure the magnetic field strength at the minimum of the magnetic antihydrogen trap to within 1.4 parts in 10^3. Hardware improvements and further study should allow this resolution to be improved by several orders of magnitude. The cyclotron resonance measurements can also be applied as a rough diagnostic of a microwave field within the ALPHA apparatus. This allowed for important diagnostics of the microwave field used to excite the PSR transitions. Finally, the experimental results demonstrating resonant PSR transitions in antihydrogen are presented. This experiment is the first ever spectroscopic measurement of antihydrogen and an important step towards future precision spectroscopy.

Timothy Peter Friesen, PhD Thesis, University of Calgary (2014)