Laser cooling antimatter hydrogen in the ALPHA trap: Hamiltonian mixing and dissipation

This talk will discuss important aspects of laser cooling the antimatter version of the hydrogen atom. The constraints of the ALPHA antihydrogen trap restrict laser access to one direction nearly along the axis of the trap. The possibility of cooling all three dimensions of motion depend on mixing the degrees of freedom in a Hamiltonian system with a nonlinear potential. Early simulations[1] suggested that a simple optical molasses from a single laser beam would be sufficient to lead to substantial laser cooling. Although the mixing is confounded by near symmetrical potential energy experienced by the antihydrogen, many of the trajectories have strong three dimensional mixing.[2] Experiments showed substantial cooling of the antihydrogen[3] using the method discussed above. Recent simulations[4] revisit this process to quantitatively describe the measurements and to propose a slight variation that could cool both trapped species of antihydrogen.

[1] P.H. Donnan, M.C. Fujiwara, and F. Robicheaux, "A proposal for laser cooling antihydrogen atoms," J. Phys. B 46, 025302 (2013).

[2] M. Zhong, J. Fajans, and A.F. Zukor, “Axial to transverse energy mixing dynamics in octupole-based magnetostatic antihydrogen traps,” New J. Phys. 20, 053003 (2018).

[3] C.J. Baker, et al (ALPHA collaboration), “Laser cooling of antihydrogen atoms,” Nature 592, 35 (2021).

[4] Spencer J. Walsh, C.O. Rasmussen, and F. Robicheaux, “Simulated optical molasses cooling of trapped antihydrogen,” J. Phys. B 58, 045202 (2025).