Cool Machines

According to the laws of thermodynamics, absolute zero (–273.15°C) cannot be reached. However, Dr Michael Köhl’s group in the Department of Physics has developed a laser-based method of cooling that has achieved almost absolute zero. At these ultracool temperatures, atoms trapped in the machine come to a standstill, allowing researchers to study their quantum nature.

‘The ability to control and cool atoms by laser light has given a completely new twist to the traditional field of atomic physics in recent years,’ explained Dr Köhl. ‘Experimentally, it only became achievable a decade ago, but it has initiated a wave of research based on access to a microscopic understanding of quantum degenerate gases.’

The Cold Atoms Group has built a machine in which six interfering laser beams are directed via a small army of lenses through rubidium gas. The laser light slows down the gas atoms, which are then subjected to evaporative cooling in a magnetic trap. For the first time ever in Cambridge, the group has recently demonstrated a Bose–Einstein condensate – essentially, atoms at close to absolute zero that have collapsed into the lowest quantum state.

‘The ultimate controllability of atoms in these states makes us optimistic about studying a whole range of phenomena linked to solid-state physics,’ said Dr Köhl. ‘Such research might provide solutions to unanswered questions in condensed matter physics and high-temperature superconductivity, as well as pave the way for quantum computers of the future.’

For more information, please contact Dr Michael Köhl (mk540@cam.ac.uk).