New experiment corrects prediction in quantum theory

Sep 19, 2012 by Donna Hesterman

An international team of scientists is rewriting a page from the quantum physics rulebook using a University of Florida laboratory once dubbed the coldest spot in the universe.

Much of what we know about quantum mechanics is theoretical and tested via computer modeling because quantum systems, like electrons whizzing around the nucleus of an atom, are difficult to pin down for observation. One can, however, slow particles down and catch them in the quantum act by subjecting them to extremely cold temperatures. New research, published in the Sept. 20 edition of the journal Nature, describes how this freeze-frame approach was recently used to overturn an accepted rule of thumb in .

"We are in the age of quantum mechanics," said Neil Sullivan, a UF physics professor and director of the High B/T Facility on the UF campus—home of the Microkelvin lab where experiments can be conducted in near-absolute zero temperatures. "If you've had an MRI, you have made use of a ."

The magnet that powers an is a transformed into a by very cold . Inside the coil, electric current flows friction free.

Quantum magnets and other strange, almost otherworldly occurrences in quantum mechanics could inspire the next big breakthroughs in computing, alternative energy and transportation technologies such as magnetic levitating trains, Sullivan said. But innovation cannot proceed without a proper set of guidelines to help engineers navigate the quantum road.

That's where the Microkelvin lab comes in. It is one of the few facilities in the world equipped to deliver the extremely needed to slow what Sullivan calls the "higgledy-piggledy" world of at normal temperatures to a manageable pace where it can be observed and manipulated.

"Room temperature is approximately 300 kelvin," Sullivan said. " pumped into a rocket at the Kennedy Space Center is at 20 kelvin."

Physicists need to cool things down to 1 millikelvin, one thousandth of a kelvin above absolute zero, or -459.67 degrees Fahrenheit, to bring matter into a different realm where quantum properties can be explored.

One fundamental state of that scientists are keen to understand more fully is a fragile, ephemeral phase of matter called a Bose-Einstein Condensate. In this state, individual particles that make up a material begin to act as a single coherent unit. It's a tricky condition to induce in a laboratory setting, but one that researchers need to explore if technology is ever to fully exploit the properties of the quantum world.

Two theorists, Tommaso Roscilde at the University of Lyon, France, and Rong Yu from Rice University in Houston, developed the underlying ideas for the study and asked a colleague, Armando Paduan-Filho from the University of Sao Paulo in Brazil, to engineer the crystalline sample used in the experiment.

"Our measurements definitively tested an important prediction about a particular behavior in a Bose-Einstein Condensate," said Vivien Zapf, a staff scientist at the National High Magnetic Field Laboratory at Los Alamos and a driving force behind the international collaboration.

The experiment monitored the atomic spin of subatomic particles called bosons in the crystal to see when the transition to Bose-Einstein Condensate was achieved, and then further cooled the sample to document the exact point where the condensate properties decayed. They observed the anticipated phenomenon when they took the sample down to 1 millikelvin.

The crystal used in the experiment had been doped with impurities in an effort to create more of a real world scenario, Zapf said. "It's nice to know what happens in pure samples, but the real world, is messy and we need to know what the quantum rules are in those situations."

Having performed a series of simulations in advance, they knew that the experiment would require them to generate temperatures down to 1 millikelvin.

"You have to go to the Microkelvin Laboratory at UF for that," she said. The lab is housed within the National High Magnetic Field Laboratory High B/T Facility at UF, funded by the National Science Foundation. Other laboratories can get to the extreme temperature required, but none of them can sustain it long enough to collect all of the data needed for the experiment.

"It took six months to get the readings," said Liang Yin, an assistant scientist in the UF physics department who operated the equipment in the Microkelvin lab. "Because the we used to control the wave intensity in the sample also heats it up. You have to adjust it very slowly."

Their findings literally rewrote the rule for predicting the conditions under which the transition would occur between the two quantum states.

"All the world should be watching what happens as we uncover properties of systems at these extremely low temperatures," Sullivan said. "A superconducting wire is superconducting because of this Bose-Einstein Condensation concept. If we are ever to capitalize on it for quantum computing or magnetic levitation for trains, we have to thoroughly understand it."

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User comments : 7

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pupsik
2.2 / 5 (5) Sep 19, 2012
If an experiment corrects a prediction of a theory then clearly the theory is either incorrect or incorrectly interpreted.
Ober
5 / 5 (4) Sep 19, 2012
The article states that the prediction is a "rule of thumb", not an absolute prediction. Therefore "rules of thumb" can be corrected without disturbing the underlying theory. Sometimes theory gets so complex that solutions are not easy to come by. In these situations "rules of thumb" are used to overcome the lack of computing power to find solutions. While "rules of thumb" are valuable QM tools, they are only ever accepted as "rules of thumb" and not an absolute prediction from theory. Once our computing power catches up, we will be able to remove "rules of thumb". Also note that "rules of thumb" by their nature, indicate that they are not always followed, it just seems as if they are. Thats how "rules of thumb" get created!!!!
Jitterbewegung
5 / 5 (4) Sep 20, 2012
So what are these new conditions and which rules did they replace?
Hakan1997
not rated yet Sep 20, 2012
I agree with Jitter, why write an article claiming that we need to rewrite a page from the quantum physics rulebook when they are not telling us what rules, what page (I want the page number) and speculating about consequences.

"All the world should be watching what happens as we uncover properties of systems at these extremely low temperatures"

Yes, we are watching with interest but we do not get the facts through Physorg.

antialias_physorg
5 / 5 (3) Sep 20, 2012
If an experiment corrects a prediction of a theory then clearly the theory is either incorrect or incorrectly interpreted.

You forget that a theory can also be incomplete. theories have boundary conditions and ranges for whichthey are good and ranges for which they are not so good (Newtons laws of motion are very good. But when you get to speeds close to c they are not so good. This doesn't make them 'incorrect'. They are still very useful for many applications.)

Theories can be tweaked, refined, augmented, ... ditching a theory just because it is off by a few percent on an observtion is not merited most of the time (and then only if you have a better one)
visual
not rated yet Sep 20, 2012
I was seriously excited by the title, hoping for evidence against the uncertainty principle, or the probability distributions in entangled systems, or something equally epic. Yes, you can say that I don't particularly like QM ;)

In retrospect I should have known better. After all, the experiment was only carried out at the Microkelvin Laboratory within the National High Magnetic Field Laboratory High B/T Facility at UF...

I guess the only experiment that may some day live up to my expectations would have to be at the HEM Building of the IAM department of UU in AM. I'm just not sure if it will be Ponder Stibbons leading it or Hex.
jibbles
not rated yet Sep 20, 2012
"higgledy-piggledy"? is this article written for 5 year olds? is it necessary for popular scientific reporting to disrespect the public's intelligence like this? all hyperbole, no substance -- none.