Rice physicists find reappearing quantum trios

Dec 11, 2009
These are borromean rings. Credit: Wikipedia

Using atoms at temperatures colder than deep space, Rice University physicists have delivered overwhelming proof for a once-scoffed-at theory that's become a hotbed for research some 40 years after it first appeared. In a paper available online in Science Express, Rice's team offers experimental evidence for a universal quantum mechanism that allows trios of particles to appear and reappear at higher energy levels in an infinite progression. The triplets, often called trimers, form in special cases where pairs cannot.

"It's such a remarkable phenomena," said team leader Randy Hulet. "There are examples, like the Borromean rings, where having a third component is crucial. Any two of the rings will unbind if the third is removed, and these trimers are similar. The particles want to bind, but no two can do it. They need the third one to make it happen."

The trimers were first predicted almost 40 years ago by Vitaly Efimov. The most striking feature of Efimov's prediction was that the effect was both universal and repeating. That meant that the trimers could form from anything, be it as large as an atom or as small as a quark. And it also meant that Efimov's trimers would form repeatedly, up and down the energy scale in a stepwise fashion. Efimov, now at the University of Washington, even predicted the spacing in energy of the trimers; he said they would appear every time the binding energy increased by a factor of 22.7.

"A lot of people didn't believe him," said Hulet, Rice's Fayez Sarofim Professor of Physics and Astronomy. "That's partly because physicists can handle two-body problems quite well and many-body problems fairly well, but when there are just a few objects, like the three bodies in these Efimov trimers, there are just too many variables."

As Hulet points out, there is still no general for the most classic of all "three-body" problems -- the sun-Earth-moon problem.

"You can do a numerical calculation, of course," he said. "You can calculate to arbitrary precision what the sun, Earth and moon are doing relative to one another at any given time, but you cannot write out a formula for that on paper. There is no general solution for that or any other three-body problem."

Researcher Randy Hulet is from Rice University. Credit: Jeff Fitlow/Rice University

What Efimov offered in 1970 was not a general solution for the three-body problem, but it was the next-best thing -- a universal relationship that would hold true for any particle but only under a particular set of circumstances.

Hulet said nuclear physicists tried for decades to find experimental evidence of Efimov trimers using nuclear particles, but they found that there wasn't a strong enough attractive interaction between the particles to satisfy the conditions laid out by Efimov.

In the 1980s, physicists began using a combination of powerful lasers and magnetic fields to trap and cool atoms to ultracold temperatures. As thermodynamic heat is driven from the atoms, they move slower and slower. That let physicists study atoms in a new way, and as the techniques progressed, physicists were eventually able to remove so much thermodynamic energy from these trapped atoms that they began to manifest the effects of quantum physics.

Efimov trimers are one manifestation of quantum physics, and Hulet said a number of research groups worldwide have been racing to study them for several years. The first Efimov trimer was observed in 2006, and the first set of two connected trimers was observed in early 2009.

In their experiments, Hulet, postdoctoral researcher Scott Pollack and graduate student Dan Dries designed a test for Efimov's prediction about universal scaling -- the notion that trimers emerged again and again in a stepwise fashion. The team used a property of ultracold atoms called a "Feshbach resonance" to tune the interactions between lithium atoms. As they dialed up and down the energy scale, they saw Efimov's trimers appear and reappear again and again. The team confirmed another Efimov prediction as well by finding four-body "tetramers" in close proximity to each trimer. In all, Hulet, Pollack and Dries found 11 different signatures for trimers and tetramers, each exactly where Efimov and others had predicted.

Efimov was in the room when Hulet presented the first results of the tests at a scientific meeting in Rome.

"He was so excited that he came up and gave me a high five after the talk," Hulet said. "In his original paper, he had a figure that looked just like what we had found. It was such an amazing prediction, and to see it borne out like this is very special."

Source: Rice University (news : web)

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User comments : 8

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3 / 5 (1) Dec 11, 2009
smells similar perhaps? Any thoughts?

"Research overturns accepted notion of neutron's electrical properties"

"Using precise data recently gathered at three different laboratories and some new theoretical tools, Gerald A. Miller, a UW physics professor, has found that the neutron has a negative charge both in its inner core and its outer edge, with a positive charge sandwiched in between to make the particle electrically neutral."
1 / 5 (4) Dec 11, 2009
smells similar perhaps? Any thoughts?

"Research overturns accepted notion of neutron's electrical properties"

"Using precise data recently gathered at three different laboratories and some new theoretical tools, Gerald A. Miller, a UW physics professor, has found that the neutron has a negative charge both in its inner core and its outer edge, with a positive charge sandwiched in between to make the particle electrically neutral."

That sounds interesting, but silly, considering that its based on an assumption that a neutron is a spherical body.
3 / 5 (3) Dec 11, 2009
September 17, 2007
"For two generations of physicists, it has been a standard belief that the neutron, an electrically neutral elementary particle and a primary component of an atom, actually carries a positive charge at its center and an offsetting negative charge at its outer edge." http://www.physor...529.html

A Britannica article made the same statement about the neutron having negative charge on the outer edge with positive charged center in 2003.
It seems very few scientist want to mention this because it does not support the quark theory of the neutron.
3 / 5 (2) Dec 11, 2009
Some type of superposition-or discrete distribution of charge? Either way, it obviously needs 'splainin', as the popular notion has always been of a homogenously charged "particle"-which it behaves as, at scale.
4.3 / 5 (3) Dec 11, 2009

Um, a neutron is composed of an Up quark with a +2/3 charge and two down quarks each with a -1/3 charge. The exact charge distribution in the particle would be very difficult to calculate from QCD. So I don't really see a problem for quark theory.
not rated yet Dec 12, 2009
it would be interesting if the internal and external negative charges were the down quarks, and the 1(of the 3) positive charge was the Up quark "between" them. Sort of like "nested" quarks in stead of the triangular traditional style of teaching it.
Dec 12, 2009
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1 / 5 (1) Dec 12, 2009
BTW Note that for particle of the same mass Yefimov three-body state becomes flat and its responsible for fractional effective charge (quantum Hall effect) in thin layers of graphene or Hahn purpur in strong magnetic fields.

Dec 12, 2009
This comment has been removed by a moderator.
4 / 5 (2) Dec 12, 2009
...because it does not support the quark theory of the neutron..
Why not, if you realize, more massive down quarks (3.5–6.0 MeV/c2) are concentrated bellow up quarks (1.5–3.3 MeV/c2) at the center of neutron, as phystic explained above. Efimov trimers illustrating the limits of formal math to describe quite simple systems, which belongs into realm of N-body theory and must be solved by particle simulations in iterative way by using of computers.

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