Waves & Packets
Aug. 3, 2013

Zeptosecond x-ray pulses can probe inner electrons and nuclear processes
Physics World
In a Physical Review Letters paper a team of physicists has proposed a plausible method for generating zeptosecond (10-21 s) x-ray pulses via IR excitation of an atomic gas. If the technique can be realized in the lab, then it could produce x-ray flashes brief enough to capture the movement of an atom's inner electrons or perhaps even look directly at the movement of protons and neutrons during nuclear fission or fusion. The proposition is that atomic electrons in IR laser field oscillate about the nucleus. Some of them actually collide with the nucleus, either in a first push by the laser field, or in a second pull when the EM field reverses direction. In the collisions the electrons give up kinetic energy, emitting a burst of broadband, coherent x-ray radiation. The to and fro collisions result in x-rays of slightly different frequencies, but the beat notes resulting from the superposition lead to sub-attosecond pulses. The team is now developing the laser technology to realize their proposition.More

Physicists discover universal law for light absorption in 2D semiconductors
Lawrence Berkeley Laboratory
Working with ultrathin membranes of the semiconductor indium arsenide, a team of researchers has discovered a quantum unit of photon absorption that should be general to all 2D semiconductors, including compound semiconductors of the III-V family that are favored for solar films and optoelectronic devices. Previous work has shown that graphene has a universal value of light absorption. In work reported in the Proceedings of the National Academy of Sciences of the United States of America, the team has now found that a similar generalized law applies to all 2D semiconductors. This discovery not only provides new insight into the basic understanding of electron–photon interactions under strong quantum confinement, i.e., the optical properties of 2D semiconductors and quantum wells, it should also open doors to exotic new optoelectronic and photonic technologies.More

Physicists control magnetic dipole in a single molecule
Karlsruhe Institute of Technology
A team of physicists have stabilized a magnetic dipole in a single-molecule junction that provides scientists with a new tool to better understand magnetism as an elementary phenomenon of physics. The molecule in the junction contained two cobalt ions, and the magnetic moment of each could be controlled by the current sent through the molecule. The magnetic state in the entire molecule became visible as Kondo anomaly, as the organometallic compound has a complex mixture of quantum states and splittings. The researchers succeeded in switching this Kondo effect on and off via the applied voltage. The experiments are described in detail in Nature Nanotechnology.More

Physicists see experimental signs of a 'new physics' beyond the Standard Model
Universitat Autònoma de Barcelona
At the EPS 2013 international conference on particle physics scientists in the LHCb collaboration presented the results of the experimental measurements of the B meson decay that showed deviations with respect to the predictions of the Standard Model. The deviations had been previously predicted, and if they hold up after more experiments it would be the first direct evidence of the existence 'new physics', i.e., a more fundamental theory than the current Standard Model. The LHCb team proved that all these deviations show a coherent pattern, and that has allowed them to identify their origin from a unique source.

In comments to Waves and Packets, Professor Gordon Kane explained that the important process, Bs →μ+μ-, the b quark and the s anti-quark combine into a Bs meson. For the process, B → K* μ+μ-, a pion anti-pion pair from the vacuum emerge, one going with the b quark to make a B meson, and the other with the anti-strange quark to make a K*. New physics can only enter in the underlying quark level process, so it will be present in both or neither. New physics would be a contribution from particles not in the Standard Model as intermediate states or in loops. But Kane expects that the B → K* one is just a fluctuation, or an artifact of systematic issues in looking at angular correlations, i.e., no new physics.

Nevertheless, in the current work, described in detail in paper posted to arXiv, researchers explain the observed pattern of deviations through a large new physics contribution to the Wilson coefficients.More

NASA's Cassini spacecraft reveals forces controlling Saturn moon jets
NASA Jet Propulsion Laboratory
The intensity of jets of water ice and organic particles that shoot out from Saturn's moon Enceladus depends on the moon's proximity to the ringed planet, according to data obtained by the Cassini spacecraft. Cassini, which has been orbiting Saturn since 2004, discovered the jets that form the plume in 2005. For years scientists hypothesized the intensity of the jets likely varied over time but no one had been able to show they changed in a recognizable pattern. These results, reported in Nature, and obtained through long term data collection using Cassini's visual and infrared mapping spectrometer, represent the first clear observation the bright plume emanating from Enceladus' south pole varies predictably. The proposition is that the planet's gravitational force puts mechanical pressure on the moon, which simply modulates the amount of material ejected from the surface just like pinching waterhose modulates the volumetric flow rate. The results also add to evidence that a body of liquid water lurks under the icy surface of the moon.More

Exoplanet found by x-ray telescope for the 1st time
Chandra X-ray Observatory
Exoplanets have primarily been determine photometrically, i.e., through optical methods. For the 1st time astronomers have found a new planet through x-ray observations. An advantageous alignment of a planet and its parent star in the system HD 189733, which is 63 light-years from Earth, enabled NASA's Chandra x-ray Observatory and the European Space Agency’s XMM Newton Observatory to observe a dip in x-ray intensity as the planet transited the star. The observations are to be reported in the Astrophysical Journal.

The planet, known as HD 189733b, is a hot Jupiter, meaning it is similar in size to Jupiter in our solar system but in very close orbit to its star. HD 189733b is more than 30 times closer to its star than Earth is to our Sun. It orbits the star once every 2.2 days. Previously astronomers used NASA's Kepler space telescope to study it at optical wavelengths, and NASA's Hubble Space Telescope was used to confirm it is blue in color as a result of the preferential scattering of blue light by silicate particles in its atmosphere.

The x-ray observations allowed astronomers to gather new knowledge about HD 189733b's atmosphere. The x-ray data suggest there are extended layers of the planet's atmosphere that are transparent to optical light but opaque to x-rays. Also astronomers have known for about a decade that ultraviolet and x-ray radiation from the main star in HD 189733 are evaporating the atmosphere of HD 189733b over time. But with these new observations the team estimates that the planet is losing 100 million to 600 million kilograms of mass per second, and that atmosphere appears to be thinning 25 percent to 65 percent faster than it would be if the planet's atmosphere were smaller.More

Speed limit for electrical switching revealed
An optical laser pulse has shattered the ordered electronic structure in an insulating sample of magnetite, switching the material to electrically conducting in a picosecond. Scientists have known the basic properties of magnetite for thousands of years, but its more exotic electronic properties are now just being learned. To affect the switch from conductor to insulator, scientists used the Linac Coherent Light Source x-ray laser to send pulses of visible laser light at the mineral. A subsequent pulse from an ultrabright, ultrashort x-ray source enabled the investigators to study the timing and details of changes in the sample excited by the initial laser strike. They discovered that it took only a picosecond to flip the on/off electrical switch in magnetite, which is thousands of times faster than in transistors now in use. In just a few hundred femotseconds after the laser pulse struck the magnetite, its electronic structure rearranged into nonconducting "islands" surrounded by electrically conducting regions. The experiments and results are described in Nature Materials.More

Letter to the editor: On rare Bs meson decays and SUSY
Waves and Packets
Dear editor: The LHC machine and experiments have performed tremendously well providing a wealth of information about the behaviour and properties of elementary particles at the electroweak scale and beyond. Recently, the LHCb and CMS experiments announced the observation of the decay of Bs mesons into muon-antimuon pairs, and some physicists have argued that these results imply that the idea of supersymmetry is in trouble. However, what these observations really imply for supersymmetry requires careful consideration. The existing Higgs boson and Bs data is not in conflict with supersymmetry.More

National Society of Black Physicists jobs board postings
Visiting Faculty Position
Scientific Director -SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East)
Staff Scientist -SLAC National Accelerator Laboratory
Department Chairperson - Howard University Physics & Astronomy
Scholar Scientist in Experimental Condensed Matter Physics and Materials Science
Director of DC Magnet Program Experimental Condensed Matter Physics and Materials Science
Stanford Synchrotron Radiation Lightsource Director
Director of SLAC Linac Coherent Light Source
BNL Postdoctoral Research Associate PositionsMore

Physicists control magnetic dipole in a single molecule
Karlsruhe Institute of Technology
A team of physicists have stabilized a magnetic dipole in a single-molecule junction that provides scientists with a new tool to better understand magnetism as an elementary phenomenon of physics.More

Physicists make new experimental verification of complementarity
Researchers in Australia have demonstrated that, contrary to what the Heisenberg uncertainty relation may suggest, particle properties such as position and momentum can be measured simultaneously with high precision.More

Observation of Bs meson decay to muons said to spell end to string theory. But is it?
The LHCb and CMS experiments at CERN have announced the first definitive observation B0s→μ+μ− decay. This is one of the rarest processes in fundamental physics, predicted by the Standard Model to occur only about 3 times in every billion.More

Latest research from Measurement Science and Technology
IOP Publishing
Development of novel optical fiber sensors for measuring tilts and displacements of geotechnical structures

Measurement scheme and simulation for the main reflector of FAST

The use of Walsh code in modulating the pump light of high spatial resolution phase-shift-pulse Brillouin optical time domain analysis with non-return-to-zero pulses

The development and characterization of a square ring shaped force transducer

Two-dimensional surface temperature diagnostics in a full-metal engine using thermographic phosphors More

Latest research from Reviews of Modern Physics
American Physical Society
Nobel Lecture: Controlling photons in a box and exploring the quantum to classical boundary

Nobel Lecture: Superposition, entanglement, and raising Schrödinger’s cat

White organic light-emitting diodes: Status and perspective

The molecular universe

Pregalactic metal enrichment: The chemical signatures of the first stars

Hydrodynamics of soft active matter

Modeling friction: From nanoscale to mesoscale

New physics search with flavor in the LHC era

Models of wave-function collapse, underlying theories, and experimental tests More