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Quantum mechanics

Where the weirdness comes from

Nature volume 395, pages 12–13 (1998)Cite this article

More than 60 years after the famous debate between Niels Bohr and Albert Einstein on the nature of quantum reality, a question central to their debate — the nature of quantum interference — has resurfaced. Dürr, Nonn and Rempe, reporting on page 33 of this issue1, have used an atom interferometer to show that Schrödinger's concept of ‘entanglement’ between the states of particles is the key to wave-particle duality, and to understanding much that is weird about quantum mechanics. This is quite different from the usual textbook explanation of duality in terms of unavoidable ‘measurement disturbances’. It confirms that entanglement is essential in establishing quantum weirdness and in the emergence of classical behaviour at larger scales.

Quantum entities can behave like particles or waves, depending on how they are observed. They can be diffracted and produce interference patterns (wave behaviour) when they are allowed to take different paths from some source to a detector — in the usual example, electrons or photons go through two slits and form an interference pattern on the screen behind. On the other hand, with an appropriate detector put along one of the paths (at a slit, say), the quantum entities can be detected at a particular place and time, as if they are point-like particles. But any attempt to determine which path is taken by a quantum object destroys the interference pattern. Richard Feynman described this as the central mystery of quantum physics.

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Figure 1: Erwin Schrödinger (left) and Niels Bohr.

References

  1. Dürr, S., Nonn, T. & Rempe, G. Nature 395, 33–37 (1998).

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  1. the Blackett Laboratory, Imperial College, London, SW7 2BZ, UK

    Peter Knight

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Knight, P. Where the weirdness comes from. Nature 395, 12–13 (1998). https://doi.org/10.1038/25592

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