Characterization of NASA Cold Atom Laboratory potentials using variational techniques*

In a recent atom-interferometry (AI) experiment, conducted aboard the NASA cold atom laboratory, a Bose-Einstein condensate (BEC) was formed too near to the atom chip wall for the AI experiment to be carried out [1]. The intent was to modify the BEC confining potential so as to move the BEC away from the atom-chip wall by tuning the external magnetic field and atom-chip currents. Unfortunately, instead of moving away from the wall, the condensate split into two pieces and the pieces flew out of the trap. Image data from the one available camera provided enough information for an estimate of an assumed unexpected stray magnetic field to match the motion captured by this camera. This estimate of the stray magnetic did not use the condensate width information contained in the images. We have used a variational approximation model for the solutions of the Gross-Pitaevskii equations [2] to refine the estimate of the stray magnetic field. We present the experimental data, the initial estimate of the stray magnetic field, our refined estimate and a program of tuning the external magnetic field and atom-chip currents that can be used to produce the intended intended motion of the condensate with the stray field present.