A study on evolution of a cold atom cloud in a time dependent radio frequency dressed potential

TL;DR

This paper uses simulations to study how a cold atom cloud evolves under a time-dependent radio frequency potential, revealing atom ejection, cooling, and formation of a toroidal trap shape, matching experimental observations.

Contribution

It introduces a simulation approach to predict atom cloud dynamics and trapping geometries in time-dependent rf potentials, extending understanding of non-adiabatic transitions.

Findings

Initial rf-field causes atom ejection and evaporative cooling.

Higher rf-field induces Landau-Zener transitions, trapping atoms in a toroidal shape.

Simulation results align with experimental observations.

Abstract

Using a Direct Simulation Monte Carlo technique, we have studied the time evolution of a cold atom cloud interacting with a time dependent radio frequency (rf) dressed state potential. Exposure of a cloud of $^{87}Rb$ atoms, trapped in a quadrupole magnetic trap, to a time dependent rf-field with increasing amplitude and decreasing frequency, shows a variation in the number of trapped atoms and the overall shape of the atom cloud. It is shown by simulations that, initially at lower rf-field strength, the rf-field results in ejection of atoms from the trap, leading to evaporative cooling of the atom cloud. Later, at higher rf-field strength, the atoms undergo the non-adiabatic Landau-Zener (LZ) transitions, which leads to their trapping in an rf-dressed state potential of toroidal shape. The results of simulations explain the experimentally observed results. The simulations can be useful to predict the atom cloud dynamics and trapping geometries with other forms of the potential.