Be⁺ assisted accumulation of Antihydrogen

Antihydrogen, the antimatter counterpart of hydrogen holds perhaps the key to resolve the baryon asymmetry problem of why bulk antimatter seems to be missing from the universe. The ALPHA collaboration has been able to synthesize and trap antihydrogen since 2010 by merging cold plasmas of antiprotons and positrons. Since 2017 we have also been able continuously synthesize additional antihydrogen inside a trap already holding antihydrogen and thus accumulate antihydrogen. The best performance was, until now, about 20 antihydrogen atoms added very synthesis cycle (about 4 min.), something that allowed the first precision measurement of the 1s-2s two photon transition in antihydrogen to a precision of 2x10^-12, and recently both laser-cooling of trapped antihydrogen and the first observation of the influence of gravity on antimatter.

Here we present the application of a novel technique that uses sympathetically cooled positrons for the synthesis. The positrons are sympathetically cooled by laser-cooled Be+ ions that are merged with the positron plasma before the synthesis. We detail how the cooling laser detuning can be used to control and improve the antihydrogen synthesis. We also discuss how our initial attempts demonstrated that parts of this new synthesis process (as well as the original) induced losses of previously accumulated antihydrogen, and discuss how we eliminated these to achieve a record pace of accumulation of almost an order of magnitude above previous records, in order to accumulate more than 15000 antihydrogen atoms in a single experiment. We discuss how this step change in antihydrogen available for experimentation has and will allow much more rapid progress, as it allows studies of systematics not previously possible on relevant timescales, as well as possible access to searches for e.g. sidereal effects that would have been inconceivable with fewer atoms accumulated at a much slower pace.