Manipulation of ultracold atoms using magnetic and optical fields

Abstract

The loading and guiding of a launched cloud of cold atoms with the optical dipole force are theoretically and numerically modelled. A far-off resonance trap can be realised using a high power Gaussian mode laser, red-detuned with respect to the principal atomic resonance (Rb 5s-5p). The optimum strategy for loading typically 30% of the atoms from a Magneto optical trap and guiding them vertically through 22 cm is discussed. During the transport the radial size of the cloud is confined to a few hundred microns, whereas the unconfined axial size grows to be approximately 1 cm. It is proposed that the cloud can be focused in three dimensions at the apex of the motion by using a single magnetic impulse to achieve axial focusing. A theoretical study of six current-carrying coil and bar arrangements that generate magnetic lenses is made. An investigation of focusing aberrations show that, for typical experimental parameters, the widely used assumption of a purely harmonic lens is often inaccurate. A new focusing regime is discussed: isotropic 3D focusing of atoms with a single magnetic lens. The baseball lens offers the best possibility for isotropically focusing a cloud of weak-field-seeking atoms in 3D.A pair of magnetic lens pulses can also be used to create a 3D focus (the alternate-gradient method). The two possible pulse sequences are discussed and it is found that they are ideal for loading both 'pancake' and 'sausage’ shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single- impulse magnetic lenses. The thesis concludes by describing the steps taken towards creating a 3D quasi- electrostatic lattice for 85Ilb， using a CՕշ laser. The resulting lattice of trapped atoms will have a low decoherence, and with resolvable lattice sites, it therefore provides a useful system to implement quantum information processing.