Bosenova: Supernova in a Bottle

Modern physicists, like the early Greek philosophers, speculate about the nature of matter in the universe. Physicists, however, have the advantage of being able to hunt for unexplored forms of reality with machines capable of producing high vacuum, low temperature, intense monochrome light, and powerful magnetic fields. All of these stark physical attributes are required for the production of a Bose-Einstein condensate (BEC), the state of matter in which thousands or millions of identical atoms act as one.

The latest bizarre discovery in the BEC realm comes from the lab of Carl Wieman at the University of Colorado, where rubidium-85 atoms are confined at 3 nano-kelvin, arguably the coldest temperature ever achieved in a lab. By slightly modifying the magnetic fields holding the Rb atoms in their condensed form within the atom trap, the interaction among the atoms can be turned from mildly repulsive to mildly attractive. The result is an implosion and subsequent explosion of atoms from the BEC, a sequence of actions analogous to what happens in a stellar supernova, albeit at an energy scale some 75 orders of magnitude smaller.

Wieman (303-492-6963; cwieman@jila.colorado) described his experiment at this week's APS meeting in Seattle. Turned to being mildly self-attractive, the Rb atoms were expected to clump together more tightly, not to explode back outwards. The surprising nova effect, like it's stellar counterpart, leads to an outward going shell or collimated jets (this "puniest explosion ever" produces about 1500 atoms at an equivalent temperature of 200 nK) and a leftover remnant. Half of the BEC atoms seem to disappear since they are not in the remnant or the expanding gas shell.

The novel atomic physics behind this "Bosenova" phenomenon is as yet unknown. Attempts to model the tiny explosion, such as by supposing that many of the atoms are paired into molecules, have all failed (see the web site). Previously Randy Hulet of Rice University had monitored the growth and collapse of a lithium BEC by adding atoms until the condensate becomes unstable, but apparently did not measure an explosive outward flow of atoms (Gerton et al., Nature, 7 December 2000).