Hyperfine Microwave Spectroscopy of Ground State Antihydrogen

In March 2012 the ALPHA Collaboration reported data from an experiment in which transitions between hyperfine levels of magnetically-trapped ground state antihydrogen atoms were selectively induced and monitored [1]. Those data comprise the first--albeit crude--direct spectroscopic probe of a pure antimatter atom, and mark the advent of an era in which precision comparisons of hydrogen and antihydrogen are expected to become a reality. I will describe the experiment that was performed by the ALPHA Collaboration, comment on its significance, and discuss prospects for hyperfine microwave spectroscopy in future tests of CPT symmetry with antihydrogen.\\[4pt] [1] Amole et al., Nature \textbf{483}, 439 (2012).