  We introduce a combined molecular dynamics (MD) and quantum trajectories (QT)
code to simulate the effects of near-resonant optical fields on state-vector
evolution and particle motion in a collisional system. In contrast to
collisionless systems, in which the quantum dynamics of multi-level,
laser-driven particles with spontaneous emission can be described with the
optical Bloch equations (OBEs), particle velocities in sufficiently collisional
systems change on timescales comparable to those of the laser-induced,
quantum-state dynamics. These transient velocity changes can cause the
time-averaged velocity dependence of the quantum state to differ from the OBE
solution. We use this multiscale code to describe laser-cooling in a strontium
ultracold neutral plasma. Important phenomena described by the simulation
include suppression of electromagnetically induced transparencies through rapid
velocity changing collisions and thermalization between cooled and un-cooled
directions for anisotropic laser cooling.
