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Quantum optics

Tricks with a single photon

Nature volume 404, pages 340–341 (2000)Cite this article

Laser light can trap atoms. But can the light field of a single photon hold an atom in free space? Because it was the development of the laser as an intense light source that made optical trapping and cooling of atoms practical, this seems to be an essentially impossible task. But now a group from the Max-Planck Institute for Quantum Optics in Munich headed by G. Rempe reports an experiment1 (on page 365of this issue) in which a single photon stored in a microcavity produces an optical force sufficient to trap an atom. Together with the related experiments on trapping and cooling of single atoms in optical cavities by H. J. Kimble's group at Caltech2, these recent advances mark a new generation of cavity quantum electrodynamics (QED) experiments1,2,3,4,5. Such work opens up exciting new avenues for basic research in quantum physics with single atoms and photons, and suggests fascinating future applications in quantum information processing.

When a laser beam is focused, an atom can experience an optical force so that it is attracted to the centre of the light focus. The same concept underlies ‘optical tweezers’, which are used to manipulate much more macroscopic particles than atoms with light fields. For intense laser beams, the optical force can be strong enough to overcome gravity. The stronger the light beam, the deeper is the optical potential that holds the atom. In addition, for an atom to remain bound in the laser focus, its thermal energy must be sufficiently small that it cannot escape. In fact, the atoms must be extremely cold in comparison with gases at room temperature, and it was only the development of laser cooling techniques during the past two decades, allowing atoms to be cooled to microkelvin temperatures, that made optical trapping of atoms possible. These achievements were honoured with the award of the 1997 Nobel Prize in Physics to Chu, Cohen–Tannoudji and Phillips.

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Figure 1: A quantum network based on cavity quantum electrodynamics (QED).

References

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  1. Institute for Theoretical Physics, University of Innsbruck, Innsbruck, 6020, Austria

    Peter Zoller

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  1. Peter Zoller
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Correspondence to Peter Zoller.

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Zoller, P. Tricks with a single photon. Nature 404, 340–341 (2000). https://doi.org/10.1038/35006185

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