Laser-Based Maxwell's Demon
Jeremy J. Thorn, Elizabeth A. Schoene, Tao Li, and Daniel A. Steck
Physical Review Letters, Editor's Suggestion (forthcoming)
A team of physicists at the University of Oregon has built a trap door for neutral atoms. The device could lead to new ways to cool atoms as well as potentially serving to guide atoms on microchips that may someday perform challenging quantum calculations.
The trap door consists of two lasers that cross the paths of neutral atoms stuck in a magneto-optical trap. The device selectively allows atoms to pass provided they are in their ground state, which means all the electrons surrounding the atoms are at the lowest energy levels they can have. The first laser is tuned to let ground state atoms through the trap door, and reject all others. The second laser is tuned to excite an atom from its ground state and into its first excited state. If an atom makes its way past the first laser and is excited by the second laser, it will not be allowed to return through the first laser again, which leaves it trapped on the downstream side of the laser doorway.
The authors describe the device as a realization of a demon imagined by nineteenth century physicist James Maxwell, who dreamed of a creature that could violate the laws of thermodynamics. The demon, Maxwell proposed, would let certain atoms through a trap door based on how hot the atoms are. Potentially, the demon could separate hot and cold atoms and use the resulting temperature difference to run a motor. Ultimately, the demon fails to violate physical laws because he is part of the system, and any gain he derives from separating atoms is wasted in the processes that keep the demon himself going.
Similarly, any thermodynamic benefit that comes from separating atoms based on their energy levels with the newly invented laser system is lost as the photons in the lasers trapping them are scattered. The laws of physics are safe from the artificial demon, but atom traps and coolers are still promising applications of the laser trap door. -JR
Speedy Sound and Cosmic Structure
Joao Magueijo
Physical Review Letters (forthcoming)
Maverick physicist Joao Magueijo (Imperial College, London) is an outspoken proponent of the idea that light may have changed speed as the universe evolved. His Varying Speed of Light (VSL) theory addresses a number of the most important features of the universe, but doesn't seem to account for some of the structures revealed in the striking images of ancient light left over from the Big Bang (also known as the Cosmic Microwave Background or CMB).
Magueijo is now arguing that gaps in the VSL theory could be filled in if cosmologists consider the effect of super high speed sound in the early universe. The modified theory provides an explanation for the fact that images of the microwave background look essentially the same regardless of how much you zoom in or out. The high speed sound offers a way that information could have been shared across the young universe, leading to the microwave structures we see today. As the universe expanded, the sound speed slowed and the patterns in the CMB were frozen in place
The proposal that light has slowed down since the Big Bang and that sound speeds may have been extraordinarily high in the early universe is a radical idea that's outside the mainstream view of most cosmologists. The general consensus in the field is that the structure of the universe and the patterns in the CMB were formed when the universe was very small and that the great distances between places that were once in intimate contact resulted from a brief phase of extreme expansion known as cosmic inflation. Although Magueijo's theories represent a drastic departure from contemporary cosmology, such long-shot ideas occasionally pay off in a big way.
For further information on Magueijo and his impassioned case for a VSL theory, see his recent special on the Science Channel, "
Joao Magueijo's Big Bang," and his popular science book
Faster than the Speed of Light.
Tilting at Electron Windmills
S. W. D. Bailey, I. Amanatidis, and C. J. Lambert
Physical Review (forthcoming)
Researchers at Lancaster University in the U. K. have calculated that electrons moving through a carbon nanotube made of atoms arranged in a pattern with a slight twist act much like the wind blowing through a pinwheel, creating enough force to rotate the cylindrical carbon molecules. Their calculations suggest a new way of designing carbon based nanomotors.
These super-tiny motors could be used as microscopic transporters in many new technologies, including the creation of nanoscale memory devices. Electron windmills could also be used to drive the movement of molecules in nanofluidic pumps, and can be applied to methods of detecting individual molecules for study. Nanofluidic pumps and single molecule detection have many applications in environmental technologies, electronics, and biology and medicine, particularly drug delivery and gene therapy. - N.R.
Beetles are a Girl’s Best Friend: Diamond Based Photonic Crystals
Jeremy W. Galusha, Lauren R. Richey, John S. Gardner, Jennifer N. Cha, and Michael H. Bartl
Physical Review E (forthcoming)
There’s more than meets the eye in the glittering green color found on the scaly shell of a Brazilian beetle called L. augustus. Using a combination of high- resolution imaging techniques, researchers at the University of Utah discovered that the beetle owes its gem-like beauty to microscopic structures that resemble the arrangements of atoms in diamond.
Naturally occurring iridescent color is often caused by tiny microstructures called photonic crystals, which manipulate light in various ways depending on their structure, rather than relying on colored pigments. Viewing the crystals from different angles results in the appearance of iridescent shifting colors, in hues as numerous as those found on the feathers of a peacock.
Unlike the color-shifting iridescence of many butterfly wings and bird feathers, L. augustus is a brilliant green color when viewed from all angles. The researchers found that the uniform color is a result of many photonic crystals arranged with slightly different angles on each of the scales that make up the weevil’s shell.
The surprisingly sophisticated source of L. augustus’ color is serving as the inspiration for manmade structures that could potentially lead to new ways to manipulate light for communication systems and optical computers. As a first step, the Utah researchers are currently attempting to make synthetic versions of the beetle’s photonic crystals by taking molds of the diamond-like scales, which they plan to reproduce in materials more suitable for computers and microelectronics than natural beetle shell. - N.R.
50 Years of PRL
Martin Blume
Physical Review Letters turns 50 this year. Martin Blume is celebrating the green journal’s birthday by summarizing the most intriguing papers to appear in PRL each year since 1958.
Past editions of Marty's Milestone PRL project.
This week, Marty is taking a look at a milestone paper from 1975 which led to the Nobel Prize in Physics in 1995 . . .
Evidence for Anomalous Lepton Production in e+-e- Annihilation
M. L. Perl et al.
Phys. Rev. Lett. 35, 1489 (1975)
When Martin Perl began his studies in the 1960's of the elementary particles called leptons there were two known members of that class: the electron and the muon, each with their associated neutrinos (see the 1962 Milestones). He was looking for the possible existence of another heavier lepton. It was not until the availability of electron-positron colliding beam storage rings that the ideal instrument for those studies became available. The SPEAR instrument at the Stanford Linear Accelerator Center, which was involved in the discovery of the psi; particle featured in the 1974 Milestones, was also used by Perl and his collaborators for the search. In the last paragraph of this Letter a claim was made by the authors for the discovery of something new, but they held back from stating that it was a new lepton. It was a long path involving many additional studies by Perl's group and by many others until other explanations of the results could be eliminated and a clear case made for the discovery of what was named the tau lepton and its associated neutrino. This "third generation" of leptons was followed also by a third generation of quarks, a parallel development for hadrons.
The 1995 Nobel Prize in Physics was awarded "for pioneering experimental contributions to lepton physics" to Martin Perl ("for the discovery of the tau lepton") and to Frederick Reines ("for the detection of the Neutrino"). The latter's research was first published in Physical Review in 1953 [Phys. Rev. 92, 830 (1953)], prior to the establishment of Physical Review Letters. See the Focus story Phys. Rev. Focus 19, story 13, for a description of this work. For further information see the Nobel press release and a recent essay by Martin Perl in Physical Review Letters.
James Riordon and Nadia Ramlagan contributed to this Tip Sheet.
