Laser cooled and trapped atoms have many applications: atomic clocks, atom
optics, optical lattices, prospects for Bose-Einstein condensation.
The density of these atoms at temperatures in the microkelvin range
is limited by collisions between the atoms. The atoms are
moving so slowly that the collision dynamics can be profoundly modified by
relatively weak light fields. Harmful collisions can be turned off by
optical shielding, by which the colliding atoms are turned around by light
while they are very far apart, thereby preventing additional interaction.
Simulating such effects requires a quantum mechanical treatment of the
system comprised of the two atoms plus the light, with dissipation due to
spontaneous emission of light during the long interaction time.
A Monte Carlo wavefunction simulation method has been developed to calculate the
density matrix of the system and the extent of optical shielding. This
requires propagating many time dependent wavepackets to build up the
density matrix. A code has been developed for this and executed in
parallel on a heterogeneous network of workstations. These extensive
calculations have allowed the development of simple models for describing the
shielding process that help explain recent experiments at NIST and elsewhere.