Fitting a Bose-Einstein Condensate inside an Atom

Ashley G. Smart

Rasmus Malthe Fiil Andersen, Stine Frederiksen, Laurits Stokholm +4 more

Experiments on Bose-Einstein condensates at finite temperature typically extract the system parameters, such as temperature, atom number, and condensed fraction from time-of-flight images taken after a free expansion time. This paper systematically examines the effect of repulsive interactions between the condensed and thermal atoms in partially condensed clouds on the expansion profile of the thermal cloud. An analytical expression for the expansion can be obtained only if the interactions between the Bose-Einstein condensate and thermal atoms are neglected, resulting in a Bose-enhanced distribution for the thermal component. Here, the deformation of the cloud due to interactions and the effects on estimated parameters are investigated by simulating the expansion using a ballistic approximation. By fitting the simulated expansion profiles with a Bose-enhanced distribution, the errors of using such a fit are estimated, and the results are explained phenomenologically. The simulation was also used as a fitting function for experimental data, showing better agreement of the extracted condensed fraction with the semi-ideal model than results from a Bose-enhanced fit.

Chen Ning Yang

Kevin Vanslette

This project focused on learning and reproducing aspects of BECs. This was accomplished through background research, calculating its density of energy states when inside a parabolic trap, finding the relationship for the critical BEC temperature for BEC inside a parabolic trap, looking in depth into the paper "Quantum Phase of a Bose-Einstein Condensate with an Arbitrary Number of Atoms" [1], performing MATLAB simulations using the paper's interference phase building method, and evaluating some simulation results.

Nikolai N Rozanov, В. А. Смирнов, Sergey V. Fedorov

It is shown theoretically that, upon filling a ring cavity (a loop magnetic waveguide) with an atomic Bose-Einstein condensate (BEC), a hysteresis dependence of the atomic number density inside the cavity on the atomic flux introduced into the cavity from the outside appears. Main parameters of the measuring system being proposed are determined: the reflectance of the magnetic mirror through which the condensate is introduced, the length of the ring cavity, and the strength of the constant magnetic field governing the BEC velocity in the cavity.

Eric Cornell, Carl Wieman