Editor's Summary
25 January 2007
A tale of two heliums
Helium-3 is a fermion, a particle, like protons, electrons and neutrons, obeying statistical rules requiring that not more than one in a set of identical particles may occupy a particular quantum state. Fermions avoid one another (a phenomenon called anti-bunching). Helium-4, though, is a boson. Bosons, like photons, pions and alpha particles, stick together and obey statistical rules that allow any number of identical particles to occupy a quantum state. Evidence for both types of quantum statistical behaviour has been observed separately, but until now no single experiment has compared the two directly. By exploiting the physical similarities of the two heliums, a team from Vrije Universiteit Amsterdam and Laboratoire Charles Fabry in Paris has succeeded in demonstrating bunching and anti-bunching behaviour of atoms in a single experiment. This is a spectacular demonstration of the role of quantum statistical effects, and could also lead to some exotic new areas of physics with cold atoms.
News and Views: Atomic physics: The social life of atoms
In a trail-blazing experiment 50 years ago, it was observed that photons from far-off stars bunch up. But in fact there's a more general distinction among free, non-interacting particles: bosons bunch, and fermions 'antibunch'.
Maciej Lewenstein
doi:10.1038/445372a
Letter: Comparison of the Hanbury Brown–Twiss effect for bosons and fermions
T. Jeltes, J. M. McNamara, W. Hogervorst, W. Vassen, V. Krachmalnicoff, M. Schellekens, A. Perrin, H. Chang, D. Boiron, A. Aspect & C. I. Westbrook
doi:10.1038/nature05513
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