Light almost stopped

This is not a new piece of work [1] to be spoken of here. It was released some a decade ago. The reason I recalled it here is because of one possible interesting demonstration with extremely slow light. Before discussing the idea, I'd like to quote the abstract of [1] below :

Techniques that use quantum interference effects are being
actively investigated to manipulate the optical properties of
quantum systems1. One such example is electromagnetically
induced transparency, a quantum effect that permits the propagation
of light pulses through an otherwise opaque medium2±5.Here
we report an experimental demonstration of electromagnetically
induced transparency in an ultracold gas of sodium atoms, in
which the optical pulses propagate at twenty million times slower
than the speed of light in a vacuum. The gas is cooled to
nanokelvin temperatures by laser and evaporative cooling6±10.
The quantum interference controlling the optical properties of
the medium is set up by a `coupling' laser beam propagating at a
right angle to the pulsed `probe' beam. At nanokelvin temperatures,
the variation of refractive index with probe frequency can
be made very steep. In conjunction with the high atomic density, this results in the exceptionally low light speeds observed. By
cooling the cloud below the transition temperature for Bose±
Einstein condensation11±13 (causing a macroscopic population of
alkali atoms in the quantum ground state of the con®ning
potential), we observe even lower pulse propagation velocities
(17ms-1) owing to the increased atom density. We report an
inferred nonlinear refractive index of 0.18 cm2W-1 and ®nd that
the system shows exceptionally large optical nonlinearities, which
are of potential fundamental and technological interest for quantum
optics.

Now let me talk about a possible use of the above work. As we know, there is interactions between photons, although such interactions are usually very weak. In vacuum, such interaction happens at about a frequency inversely proportional to the eighth power of bare (vacuum) light speed, c. The interactions can be understood in either quantum electrodynamics or classical ones (QED or CED). For simplicity, let's illustrate this with CED. According Maxwell equations, the EM fields are produced by sources, which are electrical charges and currents. These charges and currents come from of course matters (vacuum is also a kind of matter in the quantum sense, that vacuum can also interaction with other things). The whole system is thus a complex of both matter and EM fields. The laws governing the dynamics of this global system are expressed as two schools of equations: Maxwell ones and Newton's equations, the former telling EM fields how to behave while the latter dictating the matter how to behave. These two schools of equations are coupled: (1)Maxwell equations containing sources in terms of variables of matter; (2)Newton's equations containing forces coming from EM field strengths. Now if one express the matter variables in terms of EM fields through solving Newton's equations, one is able to obtain a highly nonlinear and anharmonic equations for EM fields by substituting the sources in terms of EM fields as obtained. The anharmonicity directly results in photon-photon interaction, which means, the superposition principle does not hold exactly true. Such anharmonicity is quite hard to capture in usual experiments, because it is of the order of 1/c^8 in the vacuum. On the other hand, if we can reduce light speed, such interaction shall increase. Now my idea is this: fire two light beams opposite to each other upon the sodium gas as described in [1], and these two beams shall linger in the gas due to slowing down and interact repeatedly, via generating electron-hole pairs, much the same way as in vacuum. The calculations can be easily done.

[1]Light speed reduction to 17 metres per second in an ultracold atomic gas
Lene Vestergaard Hau*², S. E. Harris³, Zachary Dutton*²
& Cyrus H. Behroozi*§
* Rowland Institute for Science, 100 Edwin H. Land Boulevard, Cambridge,
Massachusetts 02142, USA
² Department of Physics, § Division of Engineering and Applied Sciences,
Harvard University, Cambridge, Massachusetts 02138, USA
³ Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305,
USA

neutrino and antineutrino with differing masses?

This will rewrite the rules of particle physics, if it is to be confirmed:

The two experiments -- MINOS and MiniBooNE -- in their own unique ways search for a phenomenon where one type, or flavor, of neutrino (there are three: electron, muon and tau) changes into another flavor while traveling through space. Previous experiments, including MINOS, have reported evidence for such transitions, the existence of which indirectly prove that the ghostly neutrinos have non-zero, albeit tiny, masses.

In the MINOS (Main Injector Neutrino Oscillation Search) experiment a proton beam is sent to a carbon target, creating subatomic particles that decay into muon neutrinos and antineutrinos. The beam is sent 735 kilometers through solid earth, first through a near particle detector at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., and then through a 5,000-ton far particle detector in Minnesota. Scientists then measure the rates that muon neutrinos and antineutrinos convert, respectively, to tau neutrinos and antineutrinos.

Providing critical contributions to the new result, and also one of the largest groups in the MINOS collaboration, is the Indiana University High Energy & Astroparticle Physics (HEAP) group led by IU faculty members Mark Messier, Stuart Mufson, Jon Urheim and James Musser.

Urheim, an associate professor of physics, has served as one of the organizers of the working group responsible for the new measurement, providing scientific leadership during the early stage analysis; Musser, a professor of physics, has for years directed the development of the software algorithms used to convert data into physically meaningful quantities; Messier, a professor of physics, led early development of the MINOS neutrino beam model and with IU graduate and post-doctoral students has refined and improved the model over time; Mufson, an astronomy professor, is leading the analysis effort looking for violations in the expected independence of the laws governing neutrino behavior with respect to speed and direction, which might be related to the new result. The IU group, including research scientist Chuck Bower, also played key roles in the construction of MINOS.

The Standard Model of particle physics holds that particle and antiparticle masses should be equal, with no discrepancy in masses inferred from the energy scale at which the conversion process from muon to tau occurs separately for neutrinos and antineutrinos. But MINOS scientists found that not to be the case: the new results indicate that neutrino and antineutrino masses differ by about 40 percent.

"Interpreted as measurements of neutrino mass, the MINOS results give different values for neutrino and antineutrino masses," Urheim said. "Equivalence of particle and antiparticle masses is a fundamental underpinning of the well-tested Standard Model of particle physics. So, if the neutrino-antineutrino difference persists, it will necessitate a radical modification of our understanding of particle physics."

At the same time the new differences in neutrino and antineutrino behavior were being announced last week by the MINOS team, the group of MiniBooNE (Mini Booster Neutrino Experiment) scientists that includes IU associate professor of physics Rex Tayloe found muon antineutrinos turning into electron antineutrinos at a higher rate than expected. With a second discrepancy in neutrino oscillation (flavor change) uncovered, IU scientists realized the momentum building toward a reworking of the long-held Standard Model of particle physics.

"Both of these experiments indicate that neutrinos are behaving differently compared to the antineutrinos, and if either of these results hold up under further scrutiny, the implications are profound," said Tayloe, who works out of the IU Center for the Exploration of Energy and Matter (formerly the IU Cyclotron Facility). "It would likely help us to understand the imbalance of matter and anti-matter in the universe which, currently, defies explanation and is one of the 'holy grails' of current physics exploration."

Counting the number of muon antineutrinos oscillating into electron antineutrinos over a half-kilometer distance at Fermilab, MiniBooNE scientists were able to confirm a result consistent with findings from the Liquid Scintillator Neutrino Detector experiment conducted in 1990 at Los Alamos National Laboratories that found electron antineutrinos appearing about 0.25 percent of the time. But Tayloe said excitement should remain contained until the new findings are confirmed over what could be several years of continued data collection and careful checks of alternate explanations.

"Enthusiasm for these results is tempered somewhat by the realities of these very difficult experiments," he said. "The number of neutrinos/antineutrinos observed in both experiments is quite small, which means that each of these observed results could have happened by chance about 5 percent of the time even if neutrinos and anti-neutrinos behave the same. Further data collection will help to resolve this problem."

Urheim said MINOS may only double its antineutrino data set over the next few years and so noted the importance of new detectors like the $278 million NOvA (NuMI Off-Axis Electron Neutrino Appearance) detector, with which IU is also heavily involved, coming on line to further compare neutrino oscillation events.

The results of both experiments will be submitted for publication in upcoming editions of Physical Review Letters. The work is also expected to generate discussion among an international cast of scientists visiting IU Bloomington for the upcoming CPT and Lorentz Symmetry Conference, June 28-July 2, that is being hosted by the IU Physics Department and organized by IU distinguished professor of physics Alan Kostelecky.

About MINOS

Ground was broken in 2000 and data collection began in 2003. IU is a charter member of the experiment, which involves more than 140 scientists, engineers, technical specialists and students from 30 institutions in five countries: Brazil, Greece, Poland, the United Kingdom and the U.S. Funding comes from the U.S. Department of Energy and the National Science Foundation in the U.S., the Science and Technology Facilities Council in the U.K., the University of Minnesota in the U.S.; the University of Athens in Greece, and Brazil's Foundation for Research Support of the State of São Paulo and National Council of Scientific and Technological Development.

About MiniBooNE

The project began in 1997, the first beam-induced neutrino events were detected in September 2002, and the first anti-neutrino events were detected in January 2006. The experiment includes more than 80 scientists from 18 institutions in the U.S.

Provided by Indiana University (news : web)

Brownian motions under direct observation

Here is surely a very interesting report, which shall reveal a lot of details about the motions under noices. In my opinion, although many have been learned of such motions, they remain mysterious in short-time scale dynamics. Further, what about a quantum particle in noices.

Science 25 June 2010:
Vol. 328. no. 5986, pp. 1673 - 1675
DOI: 10.1126/science.1189403

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Reports
Measurement of the Instantaneous Velocity of a Brownian Particle
Tongcang Li, Simon Kheifets, David Medellin, Mark G. Raizen*

Brownian motion of particles affects many branches of science. We report on the Brownian motion of micrometer-sized beads of glass held in air by an optical tweezer, over a wide range of pressures, and we measured the instantaneous velocity of a Brownian particle. Our results provide direct verification of the energy equipartition theorem for a Brownian particle. For short times, the ballistic regime of Brownian motion was observed, in contrast to the usual diffusive regime. We discuss the applications of these methods toward cooling the center-of-mass motion of a bead in vacuum to the quantum ground motional state.

Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, TX 78712, USA.

* To whom correspondence should be addressed. E-mail: raizen@physics.utexas.edu

glass transition dynamics and surface layer mobility in unentangled polystyrene films

Science 25 June 2010: Vol. 328. no. 5986, pp. 1676 - 1679 DOI: 10.1126/science.1184394

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Reports

Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films

Zhaohui Yang,¹ Yoshihisa Fujii,¹ Fuk Kay Lee,^1,2 Chi-Hang Lam,² Ophelia K. C. Tsui^1,*

Most polymers solidify into a glassy amorphous state, accompanied by a rapid increase in the viscosity when cooled below the glass transition temperature (T_g). There is an ongoing debate on whether the T_g changes with decreasing polymer film thickness and on the origin of the changes. We measured the viscosity of unentangled, short-chain polystyrene films on silicon at different temperatures and found that the transition temperature for the viscosity decreases with decreasing film thickness, consistent with the changes in the T_g of the films observed before. By applying the hydrodynamic equations to the films, the data can be explained by the presence of a highly mobile surface liquid layer, which follows an Arrhenius dynamic and is able to dominate the flow in the thinnest films studied.

¹ Department of Physics, Boston University, Boston, MA 02215, USA.
² Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong.

^* To whom correspondence should be addressed. E-mail: okctsui@bu.edu.

eletron emisson delay experimetally seen

Look at a hydrogen atom made of a proton and an electron. Now imagine a photon impinges upon it, and the electron may be kicked out. The probability for such an event can be easily evaluated with quantum mechanics. And, according to quantum mechanics, the physics here is simple: the moment the photon disappears, the elctron is emitted. However, this is not so for a multi-electron atom. For such atoms, how an electron is thrust out by a photon is still being investigated, due to electron interactions. In this case, a senseful scenario might be like this: the photon is aborbed by the electron cloud of this atom, meanwhile the electron cloud changes to a higher energy state, and later on, this cloud relaxes to a lower energy state in the accompany of electron emission. Thus, there is a delay between the photon vanishing and electron escape. This delay is of the order of a thousandth of femtosecond, difficult to be spotted. A recent study [1] just attacks this barrier.

[1] M. Schultze et al., Science 328, 1658 (2010).

A perspective and a useful list of references on this work is found here.

Invisibility in visible light has to remain tiny?

Manipulation of light rays has entered a new era since the first proposal based on matamaterials. Such materials feature negative refraction index. The reason is because they have both negative dielectric constant and magnetic permittivity. This double-fold negativeness makes an unusual left-handed system of electric field, magnetic field and the energy current vector (which defines the light propagation direction), thus, when considering the continuity of these fields along the tangent at the interface of two meeting media, the incident light shall be deflected in a counter-intuitive manner. This behavior has been utilized to make cloaks that enables the undetection of things beneath it. Up to now, all designs apply to only longwavelength detecting rays. Is it plausible to make a cloak that works under visible light, and how ?

A recent work published in PRL seems detering the interest. It claims that, cloaks for visible light, if feasible, shall be very tiny and can not cover large objects. Nonetheless, there are oppositions to this claim, arguing that, it is rational only for resonant-type devices. So, how will this dubious topic advance further ? Let's see.

Science 25 June 2010:
Vol. 328. no. 5986, p. 1621
DOI: 10.1126/science.328.5986.1621-a

Even so, a broadband cloak cannot be much bigger than the wavelengths at which it works, Johnson and colleagues argue. In a paper in press at Physical Review Letters, they consider a simple scenario in which a pulse of light with a range of wavelengths descends on a flat object covered by a cloaking layer. If the object were not there, the light pulse would take more time to reach the surface and bounce back. So to hide the object, the cloak must delay the light pulse. And for the cloak to do that correctly over the entire wavelength range, its thickness must increase in proportion to the height of the hidden object, Johnson argues.

The thicker the cloaking layer, however, the longer the light pulse will remain in the material and the more light the cloak will absorb or scatter. If the cloak is too thick, that light loss becomes noticeable. Johnson and colleagues estimate that researchers might someday beat down the losses enough to cloak a meter-sized object at microwave wavelengths. At optical wavelengths, the losses are orders of magnitude too high to conceal such a large object, they say. A cloak for infrared or visible light cannot be more than a few micrometers across, they conclude.

Not everyone is convinced. Johnson's argument applies only to resonant systems, Pendry contends; it does not prove you cannot make a large nonresonant cloak. "It's not Moses descending from the mountain and saying you can't do it," Pendry says. "It's a rider saying that there may be some complications." Johnson says the result is general.

Cloaking is only one application for the concept of "transformation optics" that Pendry has pioneered, and others could prove more important. Still, it would be disappointing if all you could hide in your personal invisibility cloak were an eyelash.

Royal Society at its 350 anniversary

Science 25 June 2010: Vol. 328. no. 5986, p. 1611 DOI: 10.1126/science.1193400

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Editorial

The Royal Society's Wider Role

Martin Rees

The royal society is currently celebrating its 350th anniversary. In its earlier years, Christopher Wren, Robert Hooke, Robert Boyle, Samuel Pepys, and other "ingenious and curious gentlemen" met regularly in London. Their motto was to "accept nothing on authority." They did experiments, peered through newly invented telescopes and microscopes, and dissected weird animals. But, as well as indulging their curiosity, they were immersed in the practical agenda of their era: improving navigation, exploring the New World, and rebuilding London after the Great Fire of 1666. Today, our horizons have hugely expanded. Earth no longer offers an open frontier but seems constricted and crowded—a "pale blue dot" in the immense cosmos. But the Royal Society's core values have enduring relevance. Today's scientists, like their forbears, probe nature and nature's laws by observation and experiment, but they should also engage broadly with the needs of society and with public affairs.

Martin Rees is Master of Trinity College, Cambridge, UK, and president of the Royal Society.