JILA measurements recast usual view of elusive force
Physicists at JILA have demonstrated that the warmer a surface is, the stronger its subtle ability to attract nearby atoms, |
The research highlights an underappreciated aspect of the elusive Casimir-Polder force, one of the stranger effects of quantum mechanics. The force arises from the ever-present random fluctuation of microscopic electric fields in empty space. The fluctuations get stronger near a surface, and an isolated neutral atom nearby will feel them as a subtle pull—a flimsy, invisible rubber band between bulk objects and atoms that may be a source of friction, for example, in tiny devices. The JILA group previously made the most precise measurement ever of Casimir-Polder, measuring forces hundreds of times weaker than ever before and at greater distances (more than 5 micrometers). JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.
Now, as reported in a paper scheduled for this week's issue of Physical Review Letters, the JILA team has made the first measurement of the temperature dependence of this force. By using a combination of temperatures at opposite extremes—making a glass surface very hot while keeping the environment neutral and using ultracold atoms as a measurement tool—the new research underscores the power of surfaces to influence the Casimir-Polder force. That is, electric fields within the glass mostly reflect inside the surface but also leak out a little bit to greatly strengthen the fluctuations in neighboring space. As a result, says group leader and NIST Fellow Eric Cornell, "warm glass is stickier than cold glass."
The experiments demonstrate the practical use of a Bose-Einstein Condensate (BEC), a form of matter first created at JILA a decade ago. In a BEC, thousands of ultracold atoms coalesce into a "superatom" in a single quantum state. Cornell, who shared the 2001 Nobel Prize in Physics for this development, says the purity and sensitivity of a BEC makes it uniquely useful as a tool for measuring very slight forces and changes. |
The research is supported in part by the National Science Foundation. The JILA group collaborated with theorists from the University of Trento, Italy.
* J.M. Obrecht, R.J. Wild, M. Antezza, L.P. Pitaevskii, S. Stringari and E.A. Cornell. Measurement of the temperature dependence of the Casimir-Polder force. Physical Review Letters. Vol. 98, No. 6, Feb. 9, 2007.
Contact: Laura Ost laura.ost@nist.gov 303-497-4880 National Institute of Standards and Technology (NIST)
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1 comment:
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