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  • Giant Atoms Trapped with 90% Efficiency
Dec 2011
ANN ARBOR, Mich., Dec. 29, 2011 — With an “egg carton” of laser light, physicists can trap giant Rydberg atoms with up to 90 percent efficiency. The achievement could advance computing and terahertz imaging and detection devices, among other applications.

Physicists at the University of Michigan, who developed the trap, say that highly excited Rydberg atoms can be 1000 times larger than their ground state counterparts. Nearly ionized, they cling to faraway electrons almost beyond their reach. Trapping them efficiently is an important step in realizing their potential.

Giant Rydberg atoms become trapped in wells of laser light in a new, highly efficient trap developed by University of Michigan physicists, who liken it to an egg carton. (Images: Sarah Anderson)

“Our optical lattice is made from a pair of counterpropagating laser beams and forms a series of wells that can trap the atoms,similar to how an egg carton holds eggs,” said physics professor Georg Raithel.

The researchers solved the problem that had been limiting trapping efficiency to single-digit percentages. For Rydberg atoms to be trapped, they must be cooled to slow them down. The laser cooling process, however, tended to leave the atoms at the peaks of what the researchers call the “lattice hills.” But the atoms often didn’t stay there.

“To overcome this obstacle, we implemented a method to rapidly invert the lattice after the Rydberg atoms are created at the tops of the hills,” said Sarah Anderson, a physics doctoral student. “We apply the lattice inversion before the atoms have time to move away, and they therefore quickly find themselves in the bottoms of the lattice wells, where they are trapped.”

In previous Rydberg traps, atoms came to rest at the peaks of the laser light lattice, and tended to escape. University of Michigan researchers solved this problem by quickly flipping the lattice, trapping the giant Rydberg atoms in the wells, like eggs in a carton.

There is plenty of technological room left to reach the 100 percent trapping efficiency necessary for advanced applications, Raithel said.

Rydberg atoms are candidates to implement gates in future quantum computers that have the potential to solve problems too complicated for conventional computers.

The National Science Foundation and the US Department of Energy funded the work. Raithel, Anderson and recent doctoral graduate Kelly Younge were authors of a paper on the research, "Trapping Rydberg atoms in an optical lattice," published Dec. 20 in Physical Review Letters.

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laser cooling
A process and method by which manipulation and orientation of a given number of directed laser beams decreases the motion of a group of atoms or molecules such that their internal thermodynamic temperatures reach near absolute zero.  The !997 Nobel Prize in Physics was awarded to Steven Chu, Claude Cohen-Tannoudji and William D. Phillips for the development of methods to cool and trap atoms with laser light. 
laser trapping
A technique for confining atoms, molecules or small particles within one or more laser beams. This can be accomplished through the use of a single focused beam or multiple intersecting beams. With a single focused beam, the matter is confined to the laser beam's focal area. In the case of multiple intersecting beams, the matter is confined to the area of intersection because of the combined cooling effect of the beams. Also called optical trapping.
optical lattice
A periodic structure formed by intersecting or superimposed laser beams. These beams can trap atoms in low-potential regions, forming a pattern of atoms resembling the structure of a crystal.
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