Nature Commun. 5, 3089 (2014)

The standard model of particle physics predicts a CPT–symmetric Universe in which matter and antimatter are mirror images of each other: even the tiniest difference between the two would have dramatic consequences, but so far no violation of CPT symmetry has been found.

There are already high-precision measurements of the spectroscopic properties of matter atoms — such as the ground-state hyperfine splitting of hydrogen — so performing the same tests on hydrogen's antimatter twin would provide a very sensitive test of CPT symmetry. That's easier said than done, however, as it's not straightforward to produce or manipulate antihydrogen, and for spectroscopic studies large numbers of antiatoms are needed. But, in experiments at CERN's Antiproton Decelerator, Naofumi Kuroda and colleagues have taken a step forward in developing the tools needed for precision spectroscopy of antihydrogen.

Using a magnetic cusp trap, Kuroda et al. have succeeded in confining and guiding a reasonably sized sample of antihydrogen atoms (about 80, most of which are in a relatively low Rydberg state) over a distance of more than 2.5 metres towards an apparatus in which the ground-state hyperfine transition can be investigated.