Random walk simulation of phase space (3-d) cooling through unidirectional (1-d) laser interaction and trajectory energy coupling

Theories predict that the Big Bang created equal quantities of matter and antimatter, but observation shows that there is an imbalance between the two in the observable universe, the so-called baryon asymmetry problem. Studying antimatter, particularly the differences between matter-antimatter pair particles, might help explain this imbalance and lead to the discovery of new physics that could help us better understand the beginnings of the universe.

The ALPHA (Antihydrogen Laser Physics Apparatus) collaboration at CERN studies the properties of magnetically trapped antihydrogen. The kinetic energy of antihydrogen accounts for a significant amount of error on these investigations, so reducing the temperature of antihydrogen is a constant goal of the experiment. To this end, laser cooling is performed on the antihydrogen by using the Lyman alpha transition (1S-2P).

 

In the ALPHA2 apparatus, there is only one axis that the laser can be impinged onto the antihydrogen sample. 3-d cooling in ALPHA2 is achieved by individual antihydrogen atoms reflecting off the confining potential magnetic field and changing direction. In this way, changes in the energy of the antimatter ensemble parallel to the laser can eventually cause changes in the perpendicular direction and vice versa. Using this energy coupling mechanism, antihydrogen can be cooled in the direction parallel to the laser while energy from the perpendicular directions continuously mixes back into the parallel direction.

 

Instead of simulating the trajectories of antihydrogen atoms in the confining potential, I treat the coupling process in a much simpler way to avoid the computational hurdles of a first-principles simulation. It is more flexible and can give quicker results. The goal of the simulation is to better understand the dynamics of trapped 1-d cooled antihydrogen, specifically how energy mixes between the parallel and perpendicular directions. The simulation has made testable predictions to be investigated in the future, such as the possibility of "double cooling”, or performing two rounds of cooling with different settings to reach a low temperature more quickly. Understanding the dynamics of this unique process is important for reliably producing cold antihydrogen samples for other high precision studies being performed by ALPHA.