Professor Christopher Foot

Abstract:

Trapping and manipulation of cold atoms using optical potentials require the ability to generate and control a time varying light intensity distribution. Such an application demands that fast changing intensity distributions are generated, which are however free from flickering, or noise in general. Ferroelectric spatial light modulators are good candidates to achieve this because of their high refresh rate but they suffer from noise due to changes in the state of individual pixels during an animated sequence. A direct binary search based optimization routine was developed which minimizes the noise during such sequences. Filter sequences designed using this technique have been tested experimentally and the results demonstrated that flicker noise was eliminated. © 2004 Taylor & Francis Group, LLC.

Abstract:

We have observed a three-dimensional gyroscopic effect associated with a vortex in a dilute Bose-Einstein condensed gas. A condensate with a vortex possesses a single quantum of circulation, and this causes the plane of oscillation of the scissors mode to precess around the vortex line. We have measured the precession rate of the scissors oscillation. From this we deduced the angular momentum associated with the vortex line and found a value close to Planck's over 2pi per particle, as predicted for a superfluid.

Abstract:

We study the efficiency of evaporative cooling of a trapped gas of caesium atoms in the hydrodynamic regime by the numerical solution of classical kinetic theory equations. The results of the numerical simulation are compared to our experimental observations of evaporative cooling of magnetically trapped 133Cs atoms in the F = 3, MF = -3 state. The simulation accurately reproduces our experimental performance and indicates that the reduction in cooling efficiency as the gas enters the hydrodynamic regime is the main obstacle to the realization of Bose-Einstein condensation (BEC) in this state. The simulation is used to explore alternative routes to BEC.

Abstract:

We have evaporatively cooled caesium atoms in a magnetic trap to temperatures as low as 8 nK and produced a final phase space density within a factor of four of that required for the onset of Bose-Einstein condensation. At the end of the forced radio-frequency evaporation, 1500 atoms in the F = 3, mF = -3 state remain in the magnetic trap. We observe a decrease in the one-dimensional evaporative cooling efficiency at very low temperatures as the trapped sample enters the collisionally thick (hydrodynamic) regime. To alleviate this problem we propose a modified trapping scheme where three-dimensional evaporation is possible. In addition, we report measurements of the two-body inelastic collision rates for caesium atoms as a function of magnetic field. We confirm the positions, with reduced uncertainties, of three previously identified resonances at magnetic fields of 108.87(6), 118.46(3) and 133.52(3) G.

Abstract:

We have evaporatively cooled caesium atoms in a magnetic trap to temperatures as low as 8 nK and produced a final phase space density within a factor of four of that required for the onset of Bose-Einstein condensation. At the end of the forced radio-frequency evaporation, 1500 atoms in the F = 3, m(F) = -3 state remain in the magnetic trap. We observe a decrease in the one-dimensional evaporative cooling efficiency at very low temperatures as the trapped sample enters the collisionally thick (hydrodynamic) regime. To alleviate this problem we propose a modified trapping scheme where three-dimensional evaporation is possible. In addition, we report measurements of the two-body inelastic collision rates for caesium atoms as a function of magnetic field. We confirm the positions, with reduced uncertainties, of three previously identified resonances at magnetic fields of 108.87(6), 118.46(3) and 133.52(3) G.