For every particle there is an antiparticle, which is (as far as we know) a perfect mirror image, except that it has opposite charge. Mixing antiprotons and antielectrons (called positrons) one can combine them to antihydrogen, i.e. the antimatter counterpart to ordinary hydrogen. This was done by the ATHENA experiment at CERN in 2002.
I work together with the ALPHA experiment, which is a continuation of ALPHA. The goal of this experiment is to trap antihydrogen atoms, and to study them using laser spectroscopy. In this way one may find some tiny difference between matter and antimatter. Possibly, such a difference could explain why our present universe seems to contain only ordinary matter, although at the Big Bang we would expect matter and antimatter to have been created at similar amounts.
Trapping of antimatter is difficult since it annihilates as soon as it meets ordinary matter. For charged particles, such as the antiprotons and positrons electric fields can be used to hold them in place. But the antihydrogen atom is neutral so this is not possible. Instead one has to use magnetic forces. These are very weak, so the antihydrogen has to be very cold, less than about a Kelvin, to stay in the trap. Creating antihydrogen at temperatures low enough to allow trapping is a major challenge.
My own work has centered on two areas: