Magazine article Science News

Mapping Helium Atoms' Quantum States

Magazine article Science News

Mapping Helium Atoms' Quantum States

Article excerpt

Imagine, as Plato once did, prisoners chained in a cave so they can see only the shadows of things outside their prison, not the things themselves. Physicists face a similar situation in the quantum realm when they try to observe atoms and electrons in motion. They cannot see such physical objects as they are; they can only detect aspects of those objects, which appear particlelike or wavelike, depending on the type of observation.

To build up a picture of a hidden object from the different shadows it casts, one can use a method called tomography For example, one can generate an image of a person's internal organs from measurements of the intensities of X rays that have passed through in different directions.

A special sort of tomography can be used to measure the quantum state of atoms or photons. With this technique, Jurgen Mlynek and his colleagues at the University of Konstanz in Germany determined the quantum state of moving helium atoms and have shown experimentally, for the first time, that the atoms' motion has wavelike characteristics.

The researchers report their findings in the March 13 Nature.

According to quantum theory, an atom can behave like a wave. Thus, atoms traversing a pair of slits should produce an interference pattern. Atoms reach a detector only at positions where the waves reinforce each other, producing a pattern of evenly spaced bars.

Mlynek and his colleagues set up an experiment in which a beam of helium atoms passes through a pair of slits in a screen. …

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