Helium-atom beam shows coherence like lasers

March 9, 2011

Scientists from The Australian National University have developed an atom laser that behaves exactly like a light laser, opening up new possibilities for areas such as holography with atoms.

John Wallace

Canberra, Australia--Scientists from The Australian National University have developed an atom laser that behaves exactly like a light laser, opening up new possibilities for areas such as holography with atoms.¹ The group showed for the first time that a beam of helium atoms, in the form of a Bose-Einstein condensate, can be made coherent.

"If you measure the time between the arrivals of the photons in a laser beam, you find that the photons are randomly spaced, with all arrival times between photons equally probable," said Andrew Truscott, one of the researchers. "On the other hand, incoherent sources, such as a light bulb, exhibit what is called photon bunching, where it is more likely that photons arrive within a short space of time of each other." This bunching in an incoherent light source is manifested by photons arriving in pairs (second-order) or in triplets (third-order), he noted.

By cooling helium to within one millionth of a degree of absolute zero, the scientists forced the atoms to march in step and created an atom laser beam that behaves exactly like a coherent beam of photons.

No atom bunching
"Our experiment shows for the first time that the same second and third order coherence properties also apply to atoms," said team member Ken Baldwin. "This very cold atom laser also had a random distribution of arrival times with no bunching, indicating that it was perfectly coherent."

Fellow team member Robert Dall added that by warming up the atoms, the research team showed that the atoms no longer behaved coherently and once again exhibited bunching in pairs and triplets.

The research team, led by Dr Andrew Truscott of the ARC Centre of Excellence for Quantum-Atom Optics at ANU, have shown for the first time that a beam of helium atoms can be made to have properties similar to a laser light beam. The study confirms, for atoms, a theory first developed for light nearly 50 years ago by the 2005 Nobel Prize winner in physics, Roy Glauber. The work was done with PhD students Sean Hodgman and Andrew Manning and the paper on their research is published today in Science.

REFERENCE:

1. S. S. Hodgman et al., Science, 25 February 2011: 1046-1049. [DOI:10.1126/science.1198481]

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About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.