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
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
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.
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