Wave-guide:  Magnetic Atom Guides and Atom Transport

Laser cooled atoms can be confined and manipulated by magnetic fields. As the atoms move in the magnetic potential, the spin of the atom in the weak field seeking state adiabatically follows the direction of the local magnetic field. Magnetic traps have been used to confine atoms for several minutes and is used to "hold" Bose Einstein condensates during the evaporation process.

Magnetic traps that confine atoms in 3D are easy to set up. The easiest configuration uses a pair of coils in the anti-Helmholtz arrangement. One disadvantage of this setup is that the magntic field is exactly zero at the center of the trap, which can lead to trap loss from Majorana spin flips. The Ioffe-Pritchard configuration solves this problem by using a field configuration that has a non-zero minima at the trap center.

To transport atoms, one can use magnetic fields to confine atoms in 2 dimensions while leaving the atoms free to move along the 3rd dimension. This can be accomplished with 2 or 4 parallel wire structures with adjacent wires carrying currents in opposite directions. Atoms will thus be confined along the axis of the structure. In our lab, we have incorporated the atoms guide structure inside a MOT. Such a scheme will be useful for coupling cold atoms from a MOT directly into a magnetic guide.


The figure above shows a MOT formed inside a 4 wire magnetic guide structure. The structure is tilted at a small angle to allow the atoms to "flow" down the guide. In essence, this is a cold atom "slide". The strucure incorporates a tapered section which compresses the atoms by increasing the field gradient. Such a tapered section can allow the structure to be merged with a smaller magnetic guide which can compress the atoms even further. The above guide has been used to transport 10^5  Rubidium atoms over a distance of 17 cm. The picture below shows the actual atom guide itself.


One of the potential applications of building such devices is to perform evaporative cooling as the atoms move away from the MOT. One can study the feasibility of making a continous source of Bose condensates along such devices. Furthermore,  the structure that we have constructed is a very efficient way of coupling cold atoms into magnetic guides which has potential uses in atom interferometric experiments.

Reference:
Physical Review A 63 031402(R)  (2001).

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