Atom in a Magnetic Field and Crossed F-B Fields

Saverio Bivona, Bernardo Spagnolo, G. Ferrante

Symmetric resonant charge transfer in atomic collisions in the presence of a homogeneous constant magnetic field is investigated within the impact parameter method and the atomic two-state expansion. The novelties brought about by the presence of the magnetic field are discussed in detail. The most peculiar new feature is the appearance of a magnetic-field-dependent phase factor in the process wavefunction, which is responsible for severe reductions of the total cross section at moderately strong fields. Numerical evaluation of the transition probability and the total cross section is performed for the Rb + +Rb to Rb+Rb + reaction. Reduction of the cross section up to 43% are found at relative velocity nu =6.8*10 6 cm s -1 and magnetic field B=0.05 B 0 (B 0 =2.35*10 5 T being the atomic unit of magnetic strength). The magnetic field also enters the problem through a 'dressing' of the atomic states. With the values of the magnetic field strength considered, which affect the atomic energies only moderately, the dressing is found to have only secondary importance in determining the absolute values of the total cross section, which are mainly controlled by large impact parameters. Moreover the dressing is found to be important in modifying the oscillatory structure of the total cross section, which originates at small impact parameters.

Gebhard von Oppen, W. -D. Perschmann

Abstract In level-crossing experiments on high-velocity atoms, the shape of the observed signals depends sensitively on inhomogeneities of the applied magnetic field. With regard to the interpretation of such signals, we investigated the magnetic-field dependence of He I-fluorescence light excited by He-ion-He-atom collisions. Due to the inhomogeneity of the applied magnetic field, the observed level-crossing signals have a distorted shape with an oscillating structure in the wings. Taking into account the motion of the excited atoms, the shape of the signals will be explained.

Alexander Komech

Yuqing Li, Guosheng Feng, Rundong Xu +7 more

We report a detailed study of effective magnetically levitated loading of cold atoms in a crossed dipole trap: an appropriate magnetic field gradient precisely compensates for the destructive gravitational force of the atoms and an additional bias field simultaneously eliminates the antitrapping potential induced by the magnetic field gradient. The magnetic levitation is required for a large-volume crossed dipole trap to form a shallow but very effective loading potential, making it a promising method for loading and trapping more cold atoms. For cold cesium atoms in the $F=3, mF=3$ state prepared by three-dimensional degenerated Raman sideband cooling, a large number of atoms $\ensuremath{\sim}3.2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ have been loaded into a large-volume crossed dipole trap with the help of the magnetic levitation technique. The dependence of the number of atoms loaded and trapped in the dipole trap on the magnetic field gradient and bias field, respectively, is in good agreement with the theoretical analysis. The optimum magnetic field gradient of 31.13 G/cm matches the theoretical value of 31.3 G/cm well. This method can be used to obtain more cold atoms or a large number of Bose-Einstein condensation atoms for many atomic species in high-field seeking states.

Igor I Sobel'man