Physicists have wondered in recent years if they could control how atoms interact using light. Now they know that they can, by demonstrating games of quantum billiards with unusual new rules.
In an article published in the Oct. 5 issue of Physical Review Letters, a team of University of Chicago physicists explains how to tune a laser to make atoms attract or repel each other in an exotic state of matter called a Bose-Einstein condensate.
This image shows how a laser (yellow) can affect collisions between atoms (red spheres). The blue spheres depict a molecule. The laser leaves the energy of single atoms unaffected, as represented by the red surface. But the laser lowers the energy of the molecules, leading to the cup-shape of the blue surface. The stronger the laser, the more the two atoms attract each other if they collide inside the laser beam.
Credit: Chin Group/University of Chicago
"This realizes a goal that has been pursued for the past 20 years," said Cheng Chin, professor in physics at the University of Chicago, who led the team. "This exquisite control over interactions in a many-body system has great potential for the exploration of exotic quantum phenomena and engineering of novel quantum devices."
Many research groups in the United States and Europe have tried various ideas over the last decade. It was Logan Clark, a graduate student in Chin's group, who came up with the first practical solution. He has now demonstrated the idea in the lab with cesium atoms chilled to temperatures just billionths of a degree above absolute zero, and the technique can be widely applied to other atomic species.
Clark compared the process to a billiards game, when one ball encounters another. "Normally, as soon as the surfaces touch, the balls repel each other and bounce away," Clark said. In Chin's lab, cesium atoms replace the billiard balls, and ordinarily they repel each other when they collide. But by turning up the laser while operating at a "magic" wavelength, Clark showed that the repulsion between atoms can be converted into attraction.
"The atoms exhibit fascinating behavior in this system," he said. By exposing different parts of the sample to different laser intensities, "We can choose to make the atoms attract or repel each other, or pass right through each other without colliding."
Alternatively, by oscillating their interactions, analogous to making the billiard balls rapidly grow and shrink while they roll, the atoms stick to each other in pairs.
The researchers explained two fundamental ways that lasers influence the atomic motion. One is to create potentials, like a bump or valley on the billiard table, proportional to laser intensity. The new way is to alter how billiard balls collide.
"We want our laser to control collisions, but we don't want it to create any hills or valleys," Clark said. When the laser is tuned to a "magic wavelength," the beam creates no hills or valleys, but only affects collisions.
"This is because the magic wavelength happens to be in between two excited states of the atom, so they 'magically' cancel each other out," he said.
Magic is a concept that has no place in science, though the word does enjoy fairly common use among atomic physicists. "Generally it is used to refer to a wavelength at which two effects cancel or are equal, in particular when this cancellation or equality is useful for some technological goal," Clark said.
Steve Koppes | EurekAlert!
Electrocatalysis can advance green transition
23.01.2017 | Technical University of Denmark
Quantum optical sensor for the first time tested in space – with a laser system from Berlin
23.01.2017 | Ferdinand-Braun-Institut Leibniz-Institut für Höchstfrequenztechnik
For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.
According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
23.01.2017 | Health and Medicine
23.01.2017 | Physics and Astronomy
23.01.2017 | Process Engineering