Longitudianl focusing of an atomic cloud using pulsed magnetic forces

Markus Hautakorpi, A. S. Shevchenko, M. Kaivola

É. Maréchal, S. Guibal, J.-L. Bossennec +3 more

We report on a detailed study of the focusing properties of inhomogeneous magnetic fields. The experiment is performed using cold cesium atom clouds released from a magneto-optical trap. The sample longitudinal distributions are being compressed under the influence of a pulsed parabolic magnetic potential. Achromatic imaging potentialities are demonstrated. Analogies with usual optics are pointed out. A velocity compression is obtained, leading to a cloud longitudinal effective temperature down to 220 nK for a proper choice of the experimental parameters. The observation of strong compressions is corroborated by numerical simulations in excellent agreement with the experimental data. The principle of the method is presented in view of an elementary one-dimensional model and its limits are discussed.

Markus Mützel, D. Haubrich, Dieter Meschede

Matthew J Pritchard

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.

Lev Khaykovich, Nir Davidson

Aidan S. Arnold, Matthew J Pritchard, David A. Smith +1 more

We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be 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. An analysis of clouds focused by the double-impulse technique is presented.