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Ultracold neutrons

Quantum bouncing ball resonates

Nature Physics volume 7, pages 447–448 (2011)Cite this article

Spectroscopic techniques typically probe the interaction between matter and electromagnetic fields. An experiment now demonstrates that transitions between quantum states of neutrons can be brought about by mechanically vibrating a mirror, an approach that may lead to sensitive tests of gravity laws.

An extraordinary property of the neutron is that it may, provided its energy is low enough, be 'bottled' in a material vessel through its coherent scattering with nuclei at the material's surface. Neutrons of such low energies (typically of the order of a few 10−7 eV) are known as ultracold neutrons (UCNs), and have been used in a series of experiments designed to observe a variety of phenomena, and to measure important properties of the free neutron, including its lifetime, to set limits on a possible neutron electric dipole moment (see ref. 1 for an overview). Ultracold neutrons are quite rare in the thermal distributions of most modern reactor or spallation sources, where typical energies are in the range 5 to 25 meV. However, dedicated high-flux neutron sources, such as the Institut Laue–Langevin (ILL) in Grenoble, provide sufficient intensities to allow an active programme of UCN studies. A particularly striking example of a novel observation was an experiment performed a few years ago2 that provided the first observation of the discrete quantum states that result from an elementary particle bound in the gravitational potential of the Earth. Sometimes referred to as the 'quantum-mechanical bouncing ball', this example represents one of the very few truly authentic experimental realizations of the analytically soluble textbook problem of a quantum-mechanical particle in a one-dimensional potential well.

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Figure 1: Strong and heavy.

References

  1. Golub, R., Richardson, D. & Lamoreaux, S. K. Ultracold Neutrons (Taylor and Francis, 1991).

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  2. Nesvizhevsky, V. V. et al. Nature 415, 297–299 (2002).

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  3. Jenke, T., Geltenbort. P., Lemmel, H. & Abele, H. Nature Phys. 7, 468–472 (2011).

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  1. Geoffrey L. Greene is in the Department of Physics & Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA, and in the Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.,

    Geoffrey L. Greene

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  1. Geoffrey L. Greene
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Correspondence to Geoffrey L. Greene.

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Greene, G. Quantum bouncing ball resonates. Nature Phys 7, 447–448 (2011). https://doi.org/10.1038/nphys1990

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