The positron – the other component of the antihydrogen atom – also needs to be cooled as much as possible before being used for antihydrogen formation, as we have observed that the temperature of the positrons strongly influences the temperature of the antihydrogen we produce, which directly influences how much antihydrogen we can trap.

Positrons are the same mass as electrons, and so cool via cyclotron emission just as efficiently as electrons, but we are able to bring them to even lower temperatures if we utilise another technique – laser cooling. Positrons cannot be laser-cooled directly, so laser-cooled beryllium ions are mixed with our positrons, allowing the laser-cooled beryllium to sympathetically cool the positrons to lower temperatures than they would normally reach via cyclotron emission alone.