Ultracold quantum matter

Abstract:

We describe the low-energy scattering theory relevant to the description of the Bose-Einstein condensed gases recently produced using evaporative cooling. We examine the validity range of the approximations being used to describe the ultracold interactions in the context of the interaction between caesium atoms at the temperatures produced by evaporation in a magnetic trap. We discuss the prospects for future developments in the field.

Abstract:

We have constructed and characterised a novel source of slow atoms based on a pyramidal magneto optical trap with a small hole at its vertex. Atoms are first captured in the trap and then pushed through the hole by a laser beam. The size and velocity of the resulting pulses of atoms were measured. The flux of cold atoms was 1.1 × 109 atoms/s and the apparatus is readily scaleable to obtain higher fluxes. © 1998 Elsevier Science B.V. All rights reserved.

Abstract:

Caesium atoms in a magnetic trap have a higher loss rate from latin-trap collisions than rubidium under comparable conditions. We have found that this loss from inelastic collisions can be suppressed by periodic optical pumping of the atoms back into the most strongly trapped magnetic state (F = 4, MF = +4), although this reclamation of the strayed atoms gives rise to some heating of the sample. This observation shows that the dominant loss mechanism in the magnetic bias field regime investigated is from collisions which change the magnetic sublevel (quantum number MF) and not the hyperfine level (F quantum number).

Abstract:

We report on an experimental measurement of the phase shifts associated with the AC Stark effect. The optically induced light shift was measured using a Ramsey fringe technique and we have made detailed studies of the potential sources of coherence loss that can occur for an atomic sample manipulated by light. We investigated the loss of coherence due to the light shifts induced by using a non-uniform laser beam and the effects of scattered light. These measurements have implications for experiments which use optical techniques for manipulating atomic wavepackets in atom optics and atom interferometry.

Abstract:

We have investigated the properties of a standing-wave configuration of Gaussian laser beams which gives a linear array of three-dimensional atomic dipole traps. This is achieved by two counter-propagating waves with different beam waists so that at the nodes the field intensity of the standing wave is not completely cancelled at all radial positions across the beam. This creates an intensity dip in both the axial and radial directions that can be used as an atomic trap for blue detuning of the light. We simulated the behaviour of two level atoms in this trap using dressed state Monte-Carlo method and in this paper we show that it gives good trapping when the residual intensity at the bottom of the traps is small. © 1998 Elsevier Science B.V.