Matter wave interferometry cools atoms and should cool molecules

Aug. 19, 2015
University of Southampton researchers are using a new laser cooling method based on interference of matter waves.

Researchers from the University of Southampton (Southampton, England) demonstrated for the first time a new laser cooling method--based upon the interference of matter waves--that could be used to cool molecules. They say the method, which produces samples of ultra-cold atoms, could revolutionize experimental atomic physics, enabling such devices as atomic clocks (the core of GPS) and a range of quantum devices, including the possibility of a quantum computer.

RELATED ARTICLE: Solid-state laser cooling approaches liquid-nitrogen temperatures

The current technique of cooling atoms down from room temperature to the ultra-cold regime using the preferential scattering of laser photons from a particle in motion is limited to atoms with favorable electronic structure. As a result, only a small fraction of atomic elements, along with a select few diatomic molecules, have been cooled in this manner.

Described in Physical Review Letters, the research team at Southampton has provided the first proof-of-principle demonstration of a new laser cooling technique, based on a proposal by Martin Weitz and Nobel laureate Ted Hänsch in 2000, that is in principle applicable to atoms and molecules as yet untamed by conventional laser cooling. Using the new approach, which harnesses the quantum interference of matter waves, the team was able to cool a sample of already-cold Rubidium down close to the fundamental temperature limit of laser cooling.

The cooling technique is based on matter wave interferometry, in which an atom (the matter wave) is placed into a superposition of states by a laser pulse. The atom travels simultaneously along two paths that interfere at a later time, and the impulse imparted to the atom depends on the difference between these paths. The same phenomenon can be used to engineer an extremely sensitive metrological device.

Fundamentally, the impulse depends upon how the difference in energy along the two paths compares with the energy of the laser photons, where the atom’s energy is formed of potential (internal electron configuration) and kinetic (external motion) parts.

The clever trick behind Weitz and Hänsch's scheme is to make the laser interact with the atoms in such a manner as to remove the dependence on the potential energy, and thus the internal electronic structure, leaving the interference based solely on the kinetic energy of the particle. This principle of using matter wave interference to cool atoms is a significant step toward decoupling the cooling mechanism from the internal electronic structure--the 'Holy Grail' of general molecular laser cooling.

Alex Dunning, from Physics and Astronomy at the University of Southampton and lead author of the study, said, "There is a great push to extend ultra-cold physics to the rest of the periodic table to explore a greater wealth of fundamental processes and develop new technologies and we hope that our demonstration will help. While other cooling techniques can be effective they are limited to certain species and often require a multitude of lasers. Our technique, should we succeed in extending it to Weitz and Hänsch's complete scheme, would be sort of a catch-all; progress so far in cooling molecules tends to use the details of specific molecules, rather than being something general; that's why this is exciting, even though our actual experiment just uses atoms."

Group leader Tim Freegarde said, "These beautiful results have demonstrated that the method is feasible and can result in colder atoms than conventional Doppler cooling. To move on to other atoms and molecules will require more powerful lasers with shorter pulses, of the type used in coherent control chemistry, so the future of this method is very promising."

SOURCE: University of Southampton;

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.

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