Semi-classical calculations of ultracold and cold collisions with frequency-chirped light

Abstract

We conduct semi-classical Monte-Carlo simulations of ultracold collisions utilizing frequency-chirped laser light on a nanosecond timescale. Recent experiments demonstrated partial control of light-assisted collisional mechanisms with relatively slow chirp rates (10 GHz/μs). Collisions induced with positive chirped light enhance the inelastic collisional loss rate of atoms from a magneto-optical trap due to rapid adiabatic passage, whereas trap loss collisions can be coherently blocked when negative chirped light is used. Early quantum and classical simulations show that for negative chirps, the laser’s frequency continually interacts with the atom pair during the collision. We investigate how this process depends on the chirp rate and show that by moderately speeding up the chirp (>50 GHz/μs), we can significantly enhance coherent processes. We extend our semi-classical model to examine using pulse shaping as a means to coherently control collisions and show that features in the pulse shape should be on the order of or less than 1 ns. We also show that coherent control of collisions using this technique can be extended to temperatures exceeding 1 K.