Lecturer: Dr. Danielle Hodgkinson, Berkley University
Abstract:
The imbalance between matter and antimatter in the universe remains one of the big
open questions in physics. The ALPHA experiment at CERN investigates this by
synthesizing, trapping, and studying antihydrogen to compare its properties with
hydrogen. Since first trapping antihydrogen 15 years ago, ALPHA has made major
advances, including 12-digit precision spectroscopy of the 1S-2S transition [1] and, in
2023, the first direct observation that antihydrogen falls downward in Earth’s
gravitational field [2].
Further improving precision requires reducing antihydrogen energy. Laser cooling [3] is
limited by recoil effects, while adiabatic expansion cooling, an independently
demonstrated technique [4], lowers energy via slow trap expansion. Enabled by recent
advances in antihydrogen trapping, we present a hybrid cooling technique that
combines both methods, achieving a substantial reduction in antihydrogen mean
energy—around 20× lower than with laser cooling alone—reaching the millikelvin
regime. We demonstrate this technique with preliminary data showing significant
narrowing of the 1S-2S spectroscopic lineshape using hybrid cooling. This marks a
major step forward for antihydrogen experiments, unlocking the potential for
unprecedented precision in future studies, including gravitational measurements.
[1] ALPHA. Characterization of the 1S2S transition in antihydrogen. Nature, 557(7703):71–75, 2018.
[2] ALPHA. Observation of the effect of gravity on the motion of antimatter. Nature, 621(7980):716–722, 2023.
[3] ALPHA. Laser cooling of antihydrogen atoms. Nature, 592(7852):35–42, 2021.
[4] ALPHA. Adiabatic expansion cooling of antihydrogen, Phys. Rev. Research 6, L032065, 2024.