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nanotimes News in Brief

11-04 :: April/May 2011

Basic Research // Researchers in Vienna Used Sophisticated Atomchips for the Creation of Pairs of Quantum Mechanically Connected Atom-Twins

create correlated pairs of atoms using ultracold Bose- Einstein condensates. Even Einstein did not like the idea of well-separated particles still being quantum mechanically connected. He called this phenomenon “spooky action at a distance”. However, since then, the startling predictions of quantum theory have been verified in countless experiments. Quantum particles can – even if they are far apart – still belong together and “share” certain physical properties. “This does not mean that by manipulating one par- ticle we can at the same time change the other, as if they were connected by an invisible thread,” Profes- sor Jörg Schmiedmayer (TU Vienna) says, “but still, we have to treat both particles as one single quantum system – and that opens the door to fascinating new experiments.”

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Jörg Schmiedmayer’s team at the Institute for Atomic and Subatomic Physics, TU Vienna carried out the experiments, while theoretical calculations were done by Ulrich Hohensteiner, Karl Franzens University, Graz, Austria. In order to produce the quantum-correlated atoms, the scientists first create a Bose-Einstein condensate. This exotic state of matter occurs at extremely low temperatures, at less than a

t the Vienna University of Technology (TU Vienna), a method has been developed to

millionth of a degree above absolute zero. In a Bose- Einstein condensate, the atoms are in the lowest possible energy state.

“The key to success are our atomchips,” Thor- sten Schumm (TU Vienna) explains. With perfectly tailored chip structures, atoms can be manipulated with incredible precision. It is possible to deliver single quanta of vibrational energy to the atoms of the ultracold Bose-Einstein condensate. When the atoms return to the lowest energy state, the conden- sate has to get rid of the surplus energy. “Because of the sophisticated design of our atomchips, the Bose-Einstein condensate is left with only one single way to dispose of its energy: emitting pairs of atoms. All other possibilities are forbidden by quantum mechanics,” Robert Bücker (TU Vienna) explains. According to the law of momentum conservation, the two atoms move in exactly opposite directions. This process is closely related to effects in special optical crystals, in which pairs of photons can be created (so-called “optical parametric oscillators”), but now massive particles can be used instead of light.

The emitted twin atoms cannot be understood in the same way as classical particles, such as debris scattered into all directions in an explosion. They