Monorails and conveyors move supercooled atoms

Feb. 1, 2001
European researchers are continuing to make advances in the field of integrated atom optics, which seeks to control the flow and interactions of neutral atoms along well-defined paths in a manner similar to electronics and electrons.

European researchers are continuing to make advances in the field of integrated atom optics, which seeks to control the flow and interactions of neutral atoms along well-defined paths in a manner similar to electronics and electrons (see Laser Focus World, May 2000, p. 17). Researchers in Austria, Germany, and France have recently published results in three different aspects of the emerging discipline. A team working at the University of Innsbruck (Innsbruck, Austria) that recently moved to the University of Heidelberg (Heidelberg, Germany) has fabricated a monorail to guide a beam of atoms a few microns above a nanofabricated atom chip. A German group at the Max Planck Institute (Munich, Germany) devised a magnetic conveyor belt to transport 800-nm-wide atom clouds. French researchers at the University of Paris-South (Paris, France) devised a laser intersection for splitting atomic beams.

The Austrian monorail consists of current-carrying wires within a homogeneous magnetic bias field that guides a laser-cooled stream of lithium atoms parallel to the wires and through a Y-shaped beamsplitter, a few microns above a 2.5-µm-thick patterned gold layer deposited onto a gallium arsenide substrate.1 The proportion of incoming atoms that exit either leg of the Y-shaped beamsplitter is determined by changing the ratio of electric current flowing in the two output legs. Possible application areas include atom interferometry, studying decoherence processes adjacent to a surface, and quantum information processing.

French researchers have taken a different approach to the beam-splitting process, by using far off-resident atom-laser interaction. A magneto-optical trap within an ultrahigh vacuum chamber provides the rubidium-87 atoms, which are trapped and cooled there by three laser-diode beams.2 When the trapping laser beams are turned off, the atoms fall due to gravity, and about 10% are collected into a vertical guide provided by an intense far red-detuned laser beam, created with a 15-watt continuous-wave Nd:YAG laser. The falling atom beam is split by the periodic pulsing (switching time less than 500 µs) of an oblique guide (obtained by reflecting and refocusing the vertical beam) that crosses the vertical beam at an angle on the order of 0.12 rad. In this configuration the beam-splitting tends to be energy-selected, with higher-energy atoms preferring the oblique guide, yielding a potential for evaporating atoms from either a dipole or magnetic trap.

The German conveyor belt consists of a lithographic conductor patterned on a wafer in which separate potential wells enable precise velocity and position control of atomic clouds in three dimensions.3 Potential applications include interferometry experiments, atomic inkjet printing, and the atomic allegory of a charge-coupled device.


  1. D. Cassettari et al., Phys. Rev. Lett. 85, 26 (Dec. 25, 2000).
  2. O. Houde, D. Kadio, and L. Pruvost, Phy. Rev. Lett. 85, 26 (Dec. 25, 2000).
  3. W. Hansel et al., Phys. Rev. Lett. (in press).
About the Author

Hassaun A. Jones-Bey | Senior Editor and Freelance Writer

Hassaun A. Jones-Bey was a senior editor and then freelance writer for Laser Focus World.

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