|
Stunt doubles: Ultracold atoms could replicate the electron 'jitterbug'
March 11, 2008Ultracold atoms moving through a carefully designed arrangement of laser beams will jiggle slightly as they go, two NIST scientists have predicted.* If observed, this never-before-seen "jitterbug" motion would shed light on a little-known oddity of quantum mechanics arising from Paul Dirac's 80-year-old theory of the electron.
Dirac's theory, which successfully married the principles of Einstein's relativity to the quantum property of electrons known as spin, famously predicted that the electron must have an antiparticle, subsequently discovered and named the positron. More enigmatically, the Dirac theory indicates that an isolated electron moving through empty space will vibrate back and forth. But this shaking-named Zitterbewegung from the German for 'trembling motion'-is so rapid and so tiny in amplitude that it has never been directly observed.
Jay Vaishnav and Charles Clark of the Joint Quantum Institute, a partnership of NIST and the University of Maryland, have devised an experimental arrangement in which atoms are made to precisely mimic the behavior of electrons in Dirac's theory. The atoms will show Zitterbewegung-but with vibrations that are slow enough and large enough to be detected.
Vaishnav and Clark's proposal begins with an atom-rubidium-87 is an example-that has a 'tripod' arrangement of electron energy levels, consisting of one higher energy level above three equal-energy lower levels. Suppose, say the researchers, that such atoms are placed in a region crisscrossed by lasers at specific frequencies. Two pairs of laser beams face each other, creating a pattern of standing waves, while a third laser beam is set perpendicular to the other two.
Given the proper frequencies of light, a perfectly stationary "tripod" atom at the intersection will have the energy of its upper state and one of the three lower states slightly changed. To a moving atom, however, the electromagnetic field will look a little different, and in that case the energies of the other two lower states also change slightly.
Remarkably, those two states, moving in this particular arrangement of laser light, are governed by an equation that's exactly analogous to the Dirac equation for the two spin states of an electron moving in empty space. In particular, as the atom moves, it flips back and forth between the two states, and that flipping is accompanied by a jiggling back and forth of the atom's position-a version of Zitterbewegung with a frequency measured in megahertz, a hundred trillion times slower than the vibration of a free electron.
Other arrangements of lasers and atoms have been used to cleanly simulate a variety of quantum systems, says Vaishnav. Examples includes recent studies of the mechanisms of quantum magnetism and high-temperature superconductivity.** What's unusual about this new proposal, she adds, is that it offers a simulation of a fundamental elementary particle in free space and may offer access to an aspect of electron behavior that would otherwise remain beyond observational scrutiny.
###
* J.Y. Vaishnav and C.W. Clark. Observation of zitterbewegung in ultracold atoms. Presented at the March Meeting of the American Physical Society, March 10, 2008, New Orleans, La., Session A14.00003.
** I. Bloch. Towards quantum magnetism with ultracold quantum gases in optical lattices. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La., Session P7.00003. and A.M. Rey. Probing and controlling quantum magnetism with ultra-cold atoms. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La., Session P7.00004.
National Institute of Standards and Technology (NIST)
Vaishnav and Clark's proposal begins with an atom-rubidium-87 is an example-that has a 'tripod' arrangement of electron energy levels, consisting of one higher energy level above three equal-energy lower levels. Suppose, say the researchers, that such atoms are placed in a region crisscrossed by lasers at specific frequencies. Two pairs of laser beams face each other, creating a pattern of standing waves, while a third laser beam is set perpendicular to the other two.
Given the proper frequencies of light, a perfectly stationary "tripod" atom at the intersection will have the energy of its upper state and one of the three lower states slightly changed. To a moving atom, however, the electromagnetic field will look a little different, and in that case the energies of the other two lower states also change slightly.
Remarkably, those two states, moving in this particular arrangement of laser light, are governed by an equation that's exactly analogous to the Dirac equation for the two spin states of an electron moving in empty space. In particular, as the atom moves, it flips back and forth between the two states, and that flipping is accompanied by a jiggling back and forth of the atom's position-a version of Zitterbewegung with a frequency measured in megahertz, a hundred trillion times slower than the vibration of a free electron.
Other arrangements of lasers and atoms have been used to cleanly simulate a variety of quantum systems, says Vaishnav. Examples includes recent studies of the mechanisms of quantum magnetism and high-temperature superconductivity.** What's unusual about this new proposal, she adds, is that it offers a simulation of a fundamental elementary particle in free space and may offer access to an aspect of electron behavior that would otherwise remain beyond observational scrutiny.
###
* J.Y. Vaishnav and C.W. Clark. Observation of zitterbewegung in ultracold atoms. Presented at the March Meeting of the American Physical Society, March 10, 2008, New Orleans, La., Session A14.00003.
** I. Bloch. Towards quantum magnetism with ultracold quantum gases in optical lattices. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La., Session P7.00003. and A.M. Rey. Probing and controlling quantum magnetism with ultra-cold atoms. Presented at the March Meeting of the American Physical Society, March 12, 2008, New Orleans, La., Session P7.00004.
National Institute of Standards and Technology (NIST)
Ultracold Atoms News and Current Ultracold Atoms Events RSSNew method to directly probe the quantum collisions of individual atoms
The first demonstration of a fundamentally new method for measuring a particular quantum property of individual atoms will be described in a research paper to be published in the 19 April 2007 edition of the journal Nature.
Atom 'noise' may help design quantum computers
As if building a computer out of rubidium atoms and laser beams weren't difficult enough, scientists sometimes have to work as if blindfolded: The quirks of quantum physics can cause correlations between the atoms to fade from view at crucial times.
'Vortex lattices' may help explain material defects
What do you get when you superimpose a rotating pattern of intersecting laser beams on a spinning cloud of ultracold atoms in a thin gas? Pretty pictures, for one thing-but also a new method that could be used to simulate why and how defects arise in superconductors, important materials that are difficult to study directly.
Ultracold atoms produce long-sought quantum mix
In the bizarre and rule-bound world of quantum physics, every tiny speck of matter has something called "spin" - an intrinsic trait like eye color.
Ultracold test produces long-sought quantum mix
In the bizarre and rule-bound world of quantum physics, every tiny spec of matter has something called "spin"-an intrinsic trait like eye color-that cannot be changed and which dictates, very specifically, what other bits of matter the spec can share quantum space with.
MIT physicists create new form of matter
MIT scientists have brought a supercool end to a heated race among physicists: They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity.
Nature press release for 14 March issue
LIFELINES: DOUBTS CAST ON ADULT STEM CELL CLAIMS DOI: 10.1038/nature729 (Smith) 10.1038/nature730 (Terada)
Nature press release for 19 July issue
[412352] LIFELINES: TRIPLE CHECK (pp352-355; N&V) There are currently two well established main checkpoints in cell division. In this week’s Nature, researchers report a new type of checkpoint in yeast. This finding could lead to a better understanding of how cells form different tissues. For cell division to work, each daughter cell must get one complete set of chromosomes. To achieve this, the chromosomes attach to a framework of proteins called the spindle, which aligns them and pulls them to opposite poles of the cell. The newly discovered checkpoint ensures that the spindle forms in the correct position by monitoring another network of filaments, made of the protein actin, that c
More Ultracold Atoms News Articles
| © 2008 BrightSurf.com |