We demonstrate a novel dual color magneto–optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87 Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose–Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.
We demonstrate a novel dual color magneto—optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87 Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose—Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.
We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose-Einstein condensates by using a double magneto-optical trap (MOT) system that consists of a two-dimensional MOT (2D MOT) and a three-dimensional MOT (3D MOT). As an atomic beam source for loading the 3D MOT, we use a unique 2D MOT system with two-color pushing beams, which increase the loading rate and the total number of atoms in the 3D MOT, compared to a pure 2D MOT by a factor of 20. After MOT compression and polarization gradient cooling, atoms are optically pumped into a magnetically trappable hyperfine state |F = 1, m F = −1〉 to be loaded into a quadrupole-Ioffe-configuration (QUIC) trap. We enhance this optical pumping process by up to 300% by using two laser beams. After rf evaporative cooling, a Bose-Einstein condensate (BEC) with more than 2 × 107 atoms is achieved.
We present an efficient cooling scheme for fermionic
40K atoms, using laser light red and blue detuned with respect to the D2 and D1 principle fluorescence lines, respectively. The cooling scheme is found to significantly increase the saturation level for loading of a
40K magneto-optical trap (MOT), resulting in increased atom numbers or decreased cycle times. While the attainable
40K atom number is approximately doubled if exclusively
40K atoms are cooled, the scheme is particularly powerful for dual-species MOTs, for example, if
40K and
87Rb atoms are cooled simultaneously in the same MOT configuration. The typical atom losses due to light-assisted heteronuclear collisions between
40K and
87Rb seem to be reduced, giving rise to a threefold improvement of the
40K atom number as compared to that in a conventional dual-species MOT, operating merely with D2 light. Our scheme can be a useful extension to most dual-species experiments, aiming to reach simultaneous degeneracy of both species.
We have built an apparatus for setting up a double magneto-optical trap (double MOT) which allows more than 10 Rb atoms to be loaded in 15 seconds. This compact system consists mainly of a stainless steel chamber and a homemade glass cell. The two chambers are spatially separated by a small diameter transfer tube for differential pumping. The stainless steel chamber is maintained at a pressure of 10 Torr, enabling fast capturing of background Rb atoms. The optically cooled atomic clouds are pushed by a laser beam towards the glass cell which is in a much higher vacuum. Under this condition, the glass cell provides a rather long life time for holding the atoms. After the atoms are loaded in the temporarily bright MOT, a semi-dark type MOT compression is employed to reach a spatial density of 1×10 atoms/cm. The compressed atom clouds are further cooled by polarization gradient cooling to a temperature of 30 μK. The high phase space density cloud is suitable for experiments related to ultracold atoms.
We present an efficient cooling scheme for fermionic
40K atoms, using laser light red and blue detuned with respect to the
D2 and
D1 principle flourescence lines, respectively. The cooling scheme is found to significantly increase the saturation level for loading of a
40K magneto-optical trap (MOT), resulting in increased atom numbers or decreased cycle times. While the attainable
40K atom number is approximately doubled if exclusively
40K atoms are cooled, the scheme is particularly powerful for dual-species MOTs, for example, if
40K and
87Rb atoms are cooled simultaneously in the same MOT configuration. The typical atom losses due to light-assisted hetero-nuclear collisions between
40K and
87Rb seem to be reduced giving rise to a threefold improvement of the
40K atom number as compared to that in a conventional dual-species MOT, operating merely with
D2 light. Our scheme can be a useful extension to most dual-species experiments, aiming to reach simultaneous degeneracy of both species.
We demonstrate that dual dark magnetic-optical-traps (MOTs) have great importance in the two-species 87Rb and 40K mixture compared with dual bright MOTs. The dark MOT has a little improvement in the trapping of single-species 87Rb or 40K gases compared with bright MOT. For the case of loading two-species 87Rb and 40K simultaneously, the improvement of 40K in the dual dark MOTs is mainly from the reduction of light-assisted collision losses. The dual dark MOTs employ a pair of conical lenses to produce the hollow beam for repump laser with high efficiency. The number and density of 87Rb and 40K atoms after evaporative cooling in the hybrid magnetic trap with dark MOT loading are compared with those in bright MOT. The atoms with large number and high density make it easier to realize the quantum degenerate of Bose–Fermi mixture.