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'Tornadoes' Transferred From Light to Sodium Atoms

Photonics.com
Nov 2006
GAITHERSBURG, Md., Nov. 10, 2006 -- For the first time, tornado-like rotational motions have been transferred from laser light to atoms in a controlled way. The new quantum physics technique can be used to manipulate a state of matter called Bose-Einstein condensate (BEC) and possibly in quantum computing and communications systems.

As reported in the Oct. 27 issue of Physical Review Letters, the research team at the National Institute of Standards and Technology (NIST) transferred orbital angular momentum -- essentially the same motion as air molecules in a tornado or a planet revolving around a star -- from laser light to sodium atoms.TornadoeGraphic.jpg
Quantum weirdness: Images of a Bose-Einstein condensate "cloud" of sodium atoms in the NIST experiment to transfer rotational energy to a quantum system show the cloud (a) rotating in a donut-shaped vortex, (b) interfering with itself as the cloud simultaneously rotates in opposite directions, and (c) simultaneously rotates and stands still. Rotational energy is transferred in quantized amounts. False-color images show (d) one and (e) two units of rotational motion. (Image: NIST)
The researchers said the experiment completes the scientific toolkit for complete control of the state of an atom, which now includes the internal, translational and rotational behavior. The rotational motion of light previously has been used to rotate particles, but this new work marks the first time the motion has been transferred to atoms in discrete, measurable units, or quanta. Other researchers, as well as the NIST group, previously have transferred linear momentum and spin angular momentum (an internal magnetic state) from light to atoms.

The experiments were performed with more than a million sodium atoms confined in a magnetic trap. The atoms were chilled to near absolute zero and in identical quantum states, the condition known as a Bose-Einstein condensate in which they behave like a single "superatom" with a jelly-like consistency. The BEC was illuminated from opposite sides by two laser beams, one of them with a rotating doughnut shape. Each atom absorbed one photon (the fundamental particle of light) from the doughnut laser beam and emitted one photon in the path of the other laser beam, picking up the difference in orbital angular momentum between the two photons. The interaction of the two opposing lasers created a corkscrew-like interference pattern, inducing the BEC to rotate -- looking like a rotating doughnut, or a vortex similar to a hurricane.

The researchers demonstrated control over the process by inducing the cloud of atoms to simultaneously rotate and stand still, or to rotate simultaneously in opposite directions with varying amounts of momentum--a mind-bending peculiarity of quantum physics known as superposition.

The research team included staff from NIST and the Joint Quantum Institute operated by NIST and the University of Maryland, as well as guest researchers from the Indian Institute of Science, Bangalore, India; and Institut für Experimentalphysik, Universität Wien, Austria. The work was funded in part by the Office of Naval Research, NASA and the Advanced Research and Development Activity.

For more information, visit: www.nist.gov


GLOSSARY
interference
1. The additive process whereby the amplitudes of two or more overlapping waves are systematically attenuated and reinforced. 2. The process whereby a given wave is split into two or more waves by, for example, reflection and refraction of beamsplitters, and then possibly brought back together to form a single wave.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum
Smallest amount into which the energy of a wave can be divided. The quantum is proportional to the frequency of the wave. See photon.
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