How do you catch atoms? In very tiny traps

[n2doc]

By Chris Lee
Bose Einstein condensation (BEC) was one of the highlights of late 20th century physics. Scientists showed that if you cooled atoms enough, they would all get together in the same quantum state. At this point, it becomes meaningless to speak of "this" atom or "that" atom, since they are all absolutely identical and indistinguishable and can be manipulated collectively. Because they all start in the same place—quantum mechanically speaking—they all end up in the same place.

This robustness seems like it would be really useful, but there's a catch: creating a BEC requires an optical table, an enormous vacuum system, and a generally large and complicated setup. The vacuum system is unavoidable, but researchers have been working hard on miniaturizing the rest of the setup. Traps (basically wires on chips) can now hold atoms in large areas, a consequence of the low frequency currents that run through the wires and create a trapping magnetic field. To create traps that confine atoms within a few nanometers, researchers have now created traps using plasmonic fields.

How to trap an atom

Traps for neutral atoms come in three different flavors. One is called an optical molasses trap, where the Doppler shift is used to turn the atom's translational motion into light, which prevents atoms from flying away from the trap. Atoms absorb very specific frequencies of light. If an atom is moving towards the light field, the Doppler shift ensures it will see the frequency as slightly higher than a motionless atom will. If I choose my frequency carefully, moving atoms will absorb light while stationary atoms will not.

On absorbing the light, the atom gets a small kick, slowing its motion along the direction of the light beam. Furthermore, eventually it will radiate the energy, giving it a second kick in a random direction. If I use three pairs of laser beams all facing a cloud of atoms, then no matter what direction the atoms are moving, they always get driven back to the place where the laser beams meet.

more
http://arstechnica.com/science/news/2011/08/how-do-you-catch-atoms-in-very-tiny-traps.ars

[dtexdem]

1. Be vewy, vewy quiet. I'm hunting for an atom.

I'll shoot it with my twusty wights. ;-)