On loading of a magneto-optical trap on an atom-chip with U-wire quadrupole field

The role of U-wire generated quadrupole like magnetic field configuration on loading of cold $^{87}Rb$ atoms in a magneto-optical trap (MOT) on atom-chip has been investigated. It is shown by simulations that the quadrupole field profile and the center of the quadrupole field vary depending upon the U-wire current and bias field values. The result of simulations show that the resemblance of generated field configuration to the ideal quadrupole field critically depends on the values of current in U-wire and bias magnetic field. The observed number of trapped atoms in the MOT and its position has also been found to depend on the quadrupole field configuration. The number of trapped atoms in the MOT reaches maximum when the field configuration approaches close to an ideal quadrupole field. This study will help in optimising the number in the MOT before transfer of these cold atoms in the atom-chip wire trap.