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The Great Escape

Published: 10-08-2005

Have you ever wondered whether a Bose-Einstein condensate (BEC) could spontaneously escape from the trap in which it was created? After all, physicists have known for a long time that the wave nature of single particles, such as atoms and electrons, makes it possible for such particles to tunnel through all kinds of barriers that are too high to climb (or jump) over. BECs also have a wave nature because they are composed of millions of atoms in the same quantum state. In fact, a BEC can be viewed as a many-body wave function [because it consists of many bodies (atoms)].

Recently, JILA Research Associate Lincoln Carr, Fellow Murray Holland, and Professor Boris Malomed, a visitor from Tel Aviv University in Israel, decided to figure out how a many-body wave function could theoretically tunnel out of a potential well in the same way as a single atom or electron can escape from a similar trap.

"Basically, we wanted to push the limits quantum mechanics in predicting the behavior of matter," said Carr, who joined the faculty at the Colorado School of Mines in August. They discovered that quantum tunneling in a BEC system should be observable on time scales of 10 milliseconds to 10 seconds. Carr and his colleagues also wanted to explore how many atoms it would take for the laws of quantum mechanics to begin to break down and be replaced by the predictions of classical (Newtonian) physics.

With respect to quantum escapes, BECs can tunnel through a barrier, but differ from single atoms in the end result of tunneling. With a particle such as an electron, the final result, or state, of quantum tunneling is that the electron is completely out of the potential well. With a BEC, however, three final states are possible: (1) All atoms in the BEC escape from the potential well, (2) Some atoms escape via tunneling, while others remain in the well, or (3) The entire BEC jumps over the top of the well and runs down the outside as a single ring soliton before breaking up into smaller bullets known as bright vortex solitons. The formation of the soliton(s) is high-speed and violent, but entirely classical.   - Julie Phillips


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