Nobel Prize winner confirms UQ physics theory

Monday, 17 May 2004

Karen Kheruntsyan (left) and Peter Drummond

The theoretical work carried out by the UQ physicists, in collaboration with their colleagues at Ecole Normale Superiere of France (ENS), was the first calculation of spatial pair correlations of an ultra-cold gas of atoms in one-dimension.

Despite the fact that one-dimensional quantum gases were first modelled in the sixties, no exact pair correlations have been calculated in forty years. Usually, quantum correlations require supercomputers to obtain any solution.

Instead, the rigorous and exact theory employed by the theoretical team from Australia and France, used a simple combination of mathematical ideas -- without supercomputers. This was published just nine months prior to the experiment at NIST.

Experimental realization of this system requires confinement of the motion of the atoms to a thin cigar-shaped volume, which is achieved by laser beams. If the cigar length is much larger than its thickness, the motion of the atoms in the gas is essentially one-dimensional.

In addition, the atoms have to be cooled down to temperatures about a billion times colder than room temperature. Here, the properties of the atomic motion are governed by the laws of quantum physics, and the atoms behave like waves rather than particles.

When atoms with integer spin (called bosons) are cooled down to ultra-low temperatures they undergo a phase transition to a new state of matter called a Bose-Einstein condensate. This was predicted by Einstein over 70 years ago, but first realised experimentally only in 1995. The significance of this achievement was recognised soon after, in 2001, when the Nobel Prize in physics went to the researchers who demonstrated Bose-Eisntein condensation in the laboratory.

In a Bose-Einstein condensate, instead of acting as individual point-like particles the atoms behave like waves and form a gigantic matter-wave. This is very much like a laser light, in which the mass-less photons are replaced by massive atoms. To reflect these properties of Bose-Einstein condensates the physicists have introduced the term 'atom laser' and even demonstrated its operation.

In a one-dimensional environment, in addition to these striking properties, a gas of ultra-cold atoms shows further unusual quantum properties. Namely, at sufficiently low densities or strong inter-atomic interactions the bosonic atoms may start to behave like their counterparts -- fermions, which have half-integer spin.

The pair correlations in a 'fermionized' gas are suppressed below the level found in Bose-Einstein condensates. The experiments at NIST have essentially measured these correlations by means of studying the rates of collisions between the atoms under tight one-dimensional confinement. They found reduced collisional rates, which reflects the fact that the atoms have acquired fermionic properties -- in agreement with the predictions of the UQ physics theory.

References:
[1] Observation of reduced three-body recombination in a correlated 1D Bose gas. B. L. Tolra, K. M. O'Hara, J. H. Huckans, W. D. Phillips, S. L. Rolston, and J. V. Porto, Phys. Rev. Lett. 92, 190401 (2004).
[2] Pair correlations in a finite-temperature 1D Bose gas. K.V. Kheruntsyan, D.M. Gangardt, P.D. Drummond, and G.V. Shlyapnikov, Phys. Rev. Lett. 91, 040403 (2003).

Other related sites:
http://www.uq.edu.au/news/index.phtml?article=4719
http://www.abc.net.au/science/news/stories/s918573.htm
http://www.uq.edu.au/news/index.phtml?article=5366

Media:
For further information, contact: Dr Karen Kheruntsyan, phone +61-7-33653420, email kheruntsphysics.uq.edu.au; Professor Peter Drummond, phone +61-7-33653404, email drummondphysics.uq.edu.au; or Diane Hutton (Administration Officer), phone +61-7-33653427, email diane@physics.uq.edu.au, ARC Centre of Excellence for Quantum-Atom Optics, School of Physical Sciences, The University of Queensland.

http://www.physics.uq.edu.au/BEC/
http://acqao.org/
http://www.physics.uq.edu.au/