University of Queensland physicists have observed bizarre 'boomerang'-like behaviour among atoms, which may lead to new quantum technologies. Defying the laws of classical physics, a large cloud of cold atoms moving in one direction was seen to spontaneously reverse direction.
"This is an exciting new quantum physics effect that is totally forbidden by classical physics," said PhD student Winfried Hensinger. Results of the first observation of this "coherent dynamical quantum tunnelling" were published in the research journal Nature.
Hensinger's work is part of a collaboration between the groups of Nobel Laureate William Phillips at the National Institute of Standards and Technology (NIST) in Gaithersburg, USA and Professor Halina Rubinsztein-Dunlop at The University of Queensland Department of Physics.
"Quantum mechanics allows the existence of rather strange effects, one of them being quantum tunnelling, which is the surprising possibility for a particle to pass through a classically impenetrable wall," Hensinger said. Even though quantum tunnelling seems impossible, it is the basis of many electronic devices in current use.
Hensinger has taken tunnelling one step further and shown that particles can also tunnel from one motion into another motion, i.e. spontaneously change direction. A particle in a forward-moving state would normally continue in that direction. However, dynamical tunnelling allows the particle to suddenly switch to a backward-moving state without requiring any force to change its direction.
Although everyday objects do not display this spontaneous direction reversal, Hensinger and his colleagues managed to observe millions of atoms perform the feat at once. Although not the size of a cricket ball, the blob of cold atoms is visible to the naked eye.
The research teams from UQ and NIST performed the experiment by trapping a Bose-Einstein condensate, the coldest form of matter known to scientists, in an array of laser beams and magnetic fields.
"In addition to the spontaneous changes of direction, we were able to create atoms that existed in both forward- and backward-moving states simultaneously. It is a bit like creating a car that moves forward and backwards at the same time," Hensinger said.
"These experiments are of central importance to the realisation of new technologies such as those being explored in the UQ Special Research Centre for Quantum Technology. If we can understand and control the behaviour of quantum objects, a whole new world of microscopic and nanoscale technology is available to us."
For more information, contact Winfried Hensinger (in the US until August 22) email: hensinge@physics.uq.edu.au, phone: +1-301-975-4208, fax: +1-301-975-8272, (after August 22: ph: 07 33653414), Halina Rubinsztein-Dunlop at UQ Physics (telephone 07 3365 3139) or David Harris at UQ Communications (telephone 0411 528 055)
