Hot attraction: Atomic interferometry

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  • Published: Dec 15, 2017
  • Author: David Bradley
  • Channels: Atomic
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Hot bodies

Hot bodies attract atoms, contrary to what physicists had assumed. The proof is in the atom interferometry data from researchers in the USA. Steven Chu of Stanford University and formerly the University of California Berkeley, Claude Cohen-Tannoudji, and William Phillips used optical tweezers to observe the minute effect. (Credit: Chu et al/Nature)

Hot bodies attract atoms, contrary to what physicists had assumed. The proof is in the atom interferometry data from researchers in the USA. Steven Chu of Stanford University and formerly the University of California Berkeley, Claude Cohen-Tannoudji, and William Phillips used optical tweezers to observe the minute effect.

Until three years ago, when a group of Austrian physicists predicted it, no one thought that regular light, or even just the heat given off by a warm object, its infrared glow, could affect atoms in the same way. The Berkeley team is expert in measuring minute forces using atom interferometry designed an experiment to discover whether the received wisdom was in fact contrary to the actual observations. When they measured the force exerted by the so-called blackbody radiation from a warm tungsten cylinder on a caesium atom, the prediction was confirmed. The team observed an attraction 20 times stronger than the gravitational force between the two objects. Of course, gravity is the weakest of all the forces and the effect of a single caesium atom, or indeed any atom, molecule or even larger object, up to the size of asteroids and planets, is usually too small to worry about.

"It's hard to find a scenario where this force would stand out," explains team member Victoria Xu, a graduate student at UC Berkeley. "It is not clear it makes a significant effect anywhere. Yet."

Attractive force

The team points out that as our measurements of gravity become more precise, effects on this scale and of this magnitude might need to be taken into account. The researchers suggest that the next generation of experiments to detect gravitational waves from space may use a laboratory bench atom interferometer instead of the kilometre-long interferometers now in operation and so atomic attraction might become fatal to accuracy. In a typical interferometer, two light waves are combined to detect tiny changes in the distance they have traveled. In an atom interferometer, it is matter waves that are combined rather than photons to detect tiny changes in the gravitational field they have experienced. For very precise inertial navigation using atom interferometers, this "new" force would also have to be taken into account.

"This blackbody attraction has an impact wherever forces are measured precisely, including precision measurements of fundamental constants, tests of general relativity, measurements of gravity and so on," explains senior author Holger Müller. The team published details of their study in the December issue of the journal Nature Physics.

Material musing

The team measured the effect by placing a dilute gas of cold caesium atoms, cooled to three-millionths of a degree above absolute zero, in a vacuum chamber and launching them upward with a quick pulse of laser light in their optical tweezers setup.

"People think blackbody radiation is a classic concept in physics -- it was a catalyst for starting the quantum mechanical revolution 100 years ago -- but there are still cool things to learn about it," Xu muses.

Related Links

Nature Phys 2017, online: "Attractive force on atoms due to blackbody radiation"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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