Professor Christopher Foot

Abstract:

Evaporative cooling is a simple and very effective way of cooling atoms in a magnetic trap. A modelling method for this technique was developed by considering the physics of gas flow. Using this method, cross-dimensional mixing in homogeneous and inhomogeneous gases and continuous cuts in two and three dimensions are studied. The two-dimensional cut model is similar to the evaporative process in a TOP trap because atoms in this trap are removed in the basis of their radial positions. Initially, a two dimension cut retains atoms in the trap but atom loss becomes greater than with a three dimension cut because the velocity component along z is relatively hot and gives up more energetic atoms.

Abstract:

A simulation of the forced evaporative cooling process is made using a classical Monte Carlo method. This powerful method is complementary to other recent studies of evaporative cooling and does not need the assumption that a gas has recovered thermal equilibrium after each cut of potential well or the assumption of sufficient ergodicity. Direct simulation by Bird's method can be done in any arbitrary potential and can be used to study the deviation between three components of translational temperature during forced evaporation.

Abstract:

In this paper we propose a new and simple velocity selective method, which combines the velocity selective coherent population trapping of atoms in a light field and the kinetic energy coupling between the dark state and coupled state(s) during free flight, in order to reach a very narrow momentum distribution in a short period of time. This technique combined with force-assisted velocity selective coherent population trapping can produce very efficient cooling and trapping. It can also be used to overcome the cooling limit caused by the leakage of the dark state.

Abstract:

Proposed is an efficient quantum jump method that is suitable for the study of subrecoil cooling. The method is an improvement over using the numerical integration of Schrodinger equation to find delay time in which the excited state decay term is incorporated into the Hamiltonian making it a non-Hermitian matrix. It can also be applied to the calculation of three-dimensional velocity selective coherent population trapping proposed by Mauri and Arimondo in F = 3/2 to F = 3/2 transition.