These atoms are cooled to a temperature of only a few billionths of a degree above absolute zero, the coldest possible temperature, at which all motion stops.
The magnetic traps employed to hold the antihydrogen are only strong enough to confine it if it is colder than around half a degree above absolute zero.
This included quite a bit of paper pushing, and while it was an absolute waste of my college degree, it taught me quite a bit about how startup incubators work.