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Physicists at The University of Texas at Austin have discovered a new technique for cooling atoms and molecules that will allow them to study quantum physics more effectively with a greater variety of particles.

The researchers have found a way to use lasers to form walls that allow atoms and molecules to pass through in one direction, but do not allow them to return.

The technique could lead to advances in atomic clocks, which are used to standardize time worldwide.

Dr. Mark Raizen of the Center for Nonlinear Dynamics and his colleagues describe the one-way wall technique in Physical Review Letters and Europhysics Letters published earlier this year.

Raizen and his colleagues show that atoms and molecules can first be trapped in a box whose walls are built of laser light. The box can then be separated with an optical wall constructed of two lasers. These two lasers work in concert to allow atoms and molecules to pass through to one side of the box but block them from getting back to the other side. The box then has two distinct spaces, one filled with particles and one void of particles.

Raizen’s one-way wall extends the capabilities of laser and evaporative cooling, which have been limited to cooling a small number of atoms in the periodic table. The new method is applicable to a greater diversity of atoms and molecules and can expand the capability of researchers to test laws of quantum physics at extremely low temperatures.

“In nature, the cell wall is the classic example where atoms and molecules move through a one-way barrier,” Raizen said.

Cells regulate the flow of ions through one-way channels in order to create osmotic pressure. Raizen and his colleagues illustrate it is possible to create a manmade barrier to such atomic movement.

“The beauty of the one-way atomic wall,” Raizen said, “is that there is almost no increase in kinetic energy.”

With no increase in kinetic energy comes no increase in heat. By expanding and contracting the space that holds the trapped atoms and molecules, the temperature of this space, which Raizen calls a “quantum refrigerator,” can be lowered until it reaches very close to Absolute Zero.

It’s at these ultra cold temperatures, -459 degrees Fahrenheit, that quantum physicists can manipulate atoms and molecules.
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