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Terms of Entanglement

Published: 04-17-2005

Markus Greiner, Cindy Regal, Jayson Stewart, and Debbie Jin have found the first-ever visual evidence of correlated ultracold atoms in the noise patterns present in images of an ultracold cloud of potassium.

The researchers split ultracold molecules into entangled pairs of atoms flying apart in opposite directions, as shown to the right. Then they used a laser beam to create a shadow image of the cloud. They found pairs of entangled atoms by carefully studying the noise pattern in these pictures.

Similar patterns of "noise" are evident in the side-by-side images at the right, which were taken directly after potassium molecules were split into entangled atom pairs. Each picture shows the absorption of laser light by potassium atoms in one of two different energy states. High concentrations of atoms absorbing light are circled in yellow, and areas with fewer atoms are circled in green. The similar pattern in the two images shows the correlation between atoms in the different states.

Entanglement is an important, albeit counterintuitive, prediction of quantum physics. When a single atom becomes entangled with another atom, the properties of either one of them instantaneously affect the properties of its partner, even when the two atoms are far apart. Einstein called this phenomenon "spooky action at a distance." JILA researchers analyzed noise patterns in images taken of dissociated molecules to help probe the properties and limits of entanglement.

"There are interesting quantum states that are not obvious to see if you just take a picture," says JILA Fellow Debbie Jin, whose group also created the world's first fermionic condensate. "A Fermi condensate, for example, would not show up in an ordinary image. However, correlations between atoms should actually show up in the noise in these images."

Jin's group anticipates using "noisy pictures" to look for correlated atom pairs in fermionic condensates, a quantum state in which thousands of pairs of atoms behave in unison. The method could also prove to be a powerful tool in the design of quantum computers. Eventually, it could become an important detection tool for analog quantum simulators, in which condensed matter models are realized with ultracold atom systems.

The Jin Group described their new technique in the March 25 (2005) issue of Physical Review Letters.   - Julie Phillips

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