Synchronized lasers measure how light changes matter
Berkeley Lab scientists and their colleagues have successfully probed the effects of light at the atomic scale by mixing x-ray and optical light waves at the Linac Coherent Light Source
Light changes matter in ways that shape our world. Photons trigger changes in proteins in the eye to enable vision; sunlight splits water into hydrogen and oxygen and creates chemicals through photosynthesis; light causes electrons to flow in the semiconductors that make up solar cells; and new devices for consumers, industry, and medicine operate with photons instead of electrons. But directly measuring how light manipulates matter on the atomic scale has never been possible, until now.
An international team of scientists led by Thornton Glover of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) used the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory to mix a pulse of superbright x-rays with a pulse of lower frequency, "optical" light from an ordinary laser. By aiming the combined pulses at a diamond sample, the team was able to measure the optical manipulation of chemical bonds in the crystal directly, on the scale of individual atoms.
The researchers report their work in the August 30, 2012 issue of the journal Nature.
Mixing x-rays with light in x-ray diffraction
X-ray and optical wave-mixing is an x-ray diffraction technique similar to that long used in solving the structures of proteins and other biological molecules in crystalline form. But in contrast to conventional diffraction, wave mixing selectively probes how light reshapes the distribution of charge in a material. It does this by imposing a distinction between x-rays scattered from optically perturbed charge and x-rays scattered from unperturbed charge.
"You can think of the electrons orbiting atoms in a material as belonging to one of two groups," says Glover. "The 'active' electrons are the outer, loosely bound valence electrons that participate in chemical reactions and form chemical bonds. The 'spectator' electrons are the ones tightly wrapped around the nucleus at the atom's core."
Glover explains that "because the x-ray photon energy is large compared to the electron binding energy, in a typical scattering experiment all electrons scatter with comparable strength and are therefore more or less indistinguishable." The core-electron signal usually swamps the weaker valence-charge signal because there are many more core electrons than valence electrons.
"So x-rays can tell you where atoms are, but they usually can't reveal how the chemically important valence charge is distributed," Glover says. "However, when light is also present with the x-rays, it wiggles some portion of the chemically relevant valence charge. X-rays scatter from this optically driven charge, and in doing so the x-ray photon energy is changed."
The modified x-rays have a frequency (or energy) equal to the sum of the frequencies of both the original x-ray pulse and the overlapping optical pulse. The change to a slightly higher energy provides a distinct signature, which distinguishes wave mixing from conventional x-ray diffraction.
"Conventional diffraction does not provide direct information on how the valence electrons respond to light, nor on the electric fields that arise in a material because of this response," says Glover. "But with x-ray and optical wave mixing, the energy-modified x-rays selectively probe a material's optically responsive valence charge."
Beyond the ability to directly probe atomic-scale details of how light initiates such changes as chemical reactions or phase transitions, sensitivity to valence charge creates new opportunities to track the evolution of chemical bonds or conduction electrons in a material – something traditional x-ray diffraction does poorly. Different components of the valence charge can be probed by tuning the so-called optical pulse; higher-frequency pulses of extreme ultraviolet light, for example, probe a larger portion of valence charge.
Because mixing x-ray and optical light waves creates a new beam, which shows up as a slightly higher-energy peak on a graph of x-ray diffraction, the process is called "sum frequency generation." It was proposed almost half a century ago by Isaac Freund and Barry Levine of Bell Labs as a technique for probing the microscopic details of light's interactions with matter, by separating information about the position of atoms from the response of valence charge exposed to light.
But sum frequency generation requires intense x-ray sources unavailable until recently. SLAC's LCLS is just such a source. It's a free-electron laser (FEL) that can produce ultrashort pulses of high-energy "hard" x-rays millions of times brighter than synchrotron light sources, a hundred times a second.
"The breadth of the science impact of LCLS is still before us," says Jerome Hastings, a professor of photon science at the LCLS and an author of the Nature article. "What is clear is that it has the potential to extend nonlinear optics into the x-ray range as a useful tool. Wave mixing is an obvious choice, and this first experiment opens the door."
Diamonds are just the beginning
Glover's team chose diamond to demonstrate x-ray and optical wave mixing because diamond's structure and electronic properties are already well known. With this test bed, wave mixing has proved its ability to study light-matter interactions on the atomic scale and has opened new opportunities for research.
"The easiest kinds of diffraction experiments are with crystals, and there's lots to learn," Glover says. "For example, light can be used to alter the magnetic order in advanced materials, yet it's often unclear just what the light does, on the microscopic scale, to initiate these changes."
Looking farther ahead, Glover imagines experiments that observe the dynamic evolution of a complex system as it evolves from the moment of initial excitation by light. Photosynthesis is a prime example, in which the energy of sunlight is transferred through a network of light-harvesting proteins into chemical reaction centers with almost no loss.
"Berkeley Lab's Graham Fleming has shown that this virtually instantaneous energy transfer is intrinsically quantum mechanical," Glover says. "Quantum entanglement plays an important role, as an excited electron simultaneously samples many spatially separated sites, probing to find the most efficient energy-transfer pathway. It would be great if we could use x-ray and optical wave mixing to make real-space images of this process as it's happening, to learn more about the quantum aspects of the energy transfer."
Such experiments will require high pulse-repetition rates that free electron lasers have not yet achieved. Synchrotron light sources like Berkeley Lab's Advanced Light Source, although not as bright as FELs, have inherently high repetition rates and, says Glover, "may play a role in helping us assess the technical adjustments needed for high repetition-rate experiments."
Light sources with repetition rates up to a million pulses per second may someday be able to do the job. Glover says, "FELs of the future will combine high-peak brightness with high repetition rate, and this combination will open new opportunities for examining the interactions of light and matter on the atomic scale."
"X-ray and optical wave mixing," by T.E. Glover, D.M. Fritz, M. Cammarata, T.K. Allison, Sinisa Coh, J.M. Feldkamp, H. Lemke, D. Zhu, Y. Feng, R.N. Coffee, M. Fuchs, S. Ghimire, J. Chen, S. Shwartz, D.A. Reis, S.E. Harris, and J. B. Hastings, appears in the August 30, 2012 issue of Nature. The work was principally supported by the U.S. Department of Energy's Office of Science.
Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.
The Linac Coherent Light Source (LCLS), a division of SLAC National Accelerator Laboratory and a National User Facility, is operated by Stanford University for the US Department of Energy, Office of Science.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at http://science.energy.gov/.
Original release: http://www.eurekalert.org/pub_releases/2012-08/dbnl-slm082712.php


In 2007, a supergiant star two hundred times bigger than the sun was utterly obliterated by runaway thermonuclear reactions triggered by gamma ray-driven antimatter production. The resulting blast was visible for months because it unleashed a cloud of radioactive material over fifty times the size of our own star, giving off a nuclear fission glow visible from galaxies away.
SN 2007bi was discovered by the international Nearby Supernova Factory based at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The explosion ejected more than 22 solar masses of silicon and other heavy elements into space, including more than six solar masses of radioactive nickel which caused the expanding gases to glow brightly for many months.
Continue reading ""The Antimatter Supernova" --One of the Largest Cosmic Explosions Ever Recorded" »
It's no accident that we see stars in the sky, says famed Oxford biologist Richard Dawkins: they are a vital part of any universe capable of generating us. But, as Dawkins emphasizes, that does not mean that stars exists in order to make us."It is just that without stars there would be no atoms heavier than lithium in the periodic table," Dawkins wrote in The Ancestors Tale -- A Pilgrimage to the Dawn of Evolution, "and a chemistry of only three elements is too impoverished to support life. Seeing is the kind of activity that can go on only in the kind of universe where what you see is stars."
Continue reading ""Alien Edens" ----Evolutionary Biologist Richard Dawkins: 'Life Exists Elsewhere in the Universe' " »
It came suddenly from the distant reaches of the Constellation Sagittarius, some 50,000 light years away. For a brief instant, a couple of tenths of a second, on December 27, 2004, an invisible burst of energy the equivalent of half a million years of sunlight shone on Earth. Many orbiting satellites electronics were zapped and the Earth's upper atmosphere was amazingly ionized from a massive hit of gamma ray energy.
Continue reading "December 27, 2004 --The Day Planet Earth Survived Its Greatest Space-Ray Attack" »
"The answer may be that other regions of the Universe are not quite so favorable for life as we know it, and that the laws of physics we measure in our part of the Universe are merely ‘local by-laws', in which case it is no particular surprise to find life here," says John Webb of the University of New South Wales .
Continue reading ""Some Regions of the Universe are Not Favorable for Life" " »
"Of all the many glorious images we have received from Saturn, none are more strikingly unusual than those taken from Saturn's shadow," said Carolyn Porco, Cassini's imaging team lead based at the Space Science Institute in Boulder, Colo.
Continue reading "Image of the Day: Inside the Shadow of Saturn" »
In a major paper in Science, Perimeter Faculty member Xiao-Gang Wen reveals a modern reclassification of all 500 phases of matter. Using modern mathematics, Wen and collaborators reveal a new system which can, at last, successfully classify symmetry-protected phases of matter. Their new classification system will provide insight about these quantum phases of matter, which may in turn increase our ability to design states of matter for use in superconductors or quantum computers. The paper provides a revealing look at the intricate and fascinating world of quantum entanglement, and an important step toward a modern reclassification of all phases of matter.
Continue reading "Quantum Entanglement is Creating New Classifications of All Phases of Matter" »
Astronomers have come to realize that the process of star formation, once thought to consist essentially of just the simple coalescence of material by gravity, occurs in a complex series of stages. As the gas and dust in giant molecular clouds comes together into stars, dramatic outflowing jets of material develop around each, as do circumstellar disks (possibly pre-planetary in nature). Other features are present as well: Astronomers in the 1960s were amazed to discover that these star-forming regions sometimes produce natural masers (masers are the bright, radio wavelength analogs of lasers). Clouds of water vapor or methanol vapor in regions of active star formation generate some of the most spectacular masers.
Continue reading "Holiday Weekend Image: A Spectacular Masar" »
The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. As Enrico Fermi asked if the Universe is conducive to intelligent life, “Where is everybody?”
Continue reading "Advanced ET Civilizations May Be Impossible to Detect (Holiday Weekend Feature)" »
"Even if there is only 1 intelligent civilization per galaxy where you have over 100 billion stars per galaxy with some galaxies sporting nearer to a trillion stars. There are over 100 billion galaxies in the visible universe, maybe more. So even assuming you have only 1 species per galaxy, that's still 100 billion x 100 billion possible life sustaining solar systems. Which is probably a small estimate. We know that the building blocks of life are present more or less everywhere in the universe."
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Continue reading "Comment of the Day: Advanced ET Civilizations May Be Impossible to Detect (Holiday Weekend Feature)" »


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One of the responsibilities for us as researchers is to have the courage to challenge accepted "truths" and to seek out new insights. Richard Feynman was a physicist who not only epitomized both of these qualities in his research but also took enormous pleasure in communicating the ideas of physics to students. Feynman won the Nobel Prize for his computational toolkit that we now call Feynman Diagrams. The techniques he developed helped the physics community make sense of Quantum Electrodynamics (QED) after the war, when the entire community was in a state of confusion about how to handle the infinities that appeared all over the place when one tried to make a perturbative expansion in the coupling.
Feynman was the subject of a recent TEDxCaltech conference, fittingly called, "Feynman's Vision: The Next 50 Years." The event was organized in recognition of the 50-year anniversary of Feynman's visionary talk, "There's Plenty of Room at the Bottom," in which he set out a vision for nanoscience that is only now beginning to be realized. It is also 50 years since he gave his revolutionary "Feynman Lectures on Physics," which educated generations of physicists.
I had the honor of speaking about Feynman's contributions to computing, from his days at Los Alamos during the war, his Nobel Prize winning computational toolkit (Feynman Diagrams), and his invention of quantum computing, By striving to think differently, he truly changed the world. The following are some highlights from my presentation.
Parallel Computing Without Computers
Feynman worked on the Manhattan Project at Los Alamos in the 1940s with Robert Oppenheimer, Hans Bethe, and Edward Teller. In order to make an atom bomb from the newly-discovered trans-uranic element, Plutonium, it was necessary to generate a spherical compression wave to compress the Plutonium to critical mass for the chain reaction to start. It was, therefore, necessary to calculate how to position explosive charges in a cavity to generate such a compression wave; these calculations were sufficiently complex that they had to be done numerically. The team assigned to perform these calculations was known as the "IBM team," but it should be stressed that this was in the days before computers and the team operated on decks of cards with adding machines, tabulators, sorters, collators, and so on. The problem was that the calculations were taking too long, so Feynman was put in charge of the IBM team.
Feynman immediately discovered that because of the obsession with secrecy at Los Alamos, the team members had no idea of the significance of their calculations or why they were important for the war effort. He went straight to Oppenheimer and asked for permission to brief the team about the importance of their implosion calculations. He also discovered a way to speed up the calculations. By assigning each problem to a different colored deck of cards, the team could work on more than one problem at once. While one deck was using one of the machines for one stage of the calculation, another deck could be using a different machine for a different stage of its calculation. In essence, this is a now-familiar technique of parallel computing—the pipeline parallelism familiar from the Cray vector supercomputers, for example.
The result was a total transformation. Instead of completing only three problems in nine months, the team was able to complete nine problems in three months! Of course, this led to a different problem when management reasoned that it should be possible to complete the last calculation needed for the Trinity test in less than a month. To meet this deadline, Feynman and his team had to address the more difficult problem of breaking up a single calculation into pieces that could be performed in parallel.
My next story starts in 1948 at the Pocono Conference where all the great figures of physics—Niels Bohr, Paul Dirac, Robert Oppenheimer, Edward Teller, and so on—had assembled to try to understand how to make sense of the infinities in QED. Feynman and Schwinger were the star speakers, but Feynman was unable to make his audience understand how he did his calculations. His interpretation of positrons as negative energy electrons moving backwards in time was just too hard for them to accept. After the conference, Feynman was in despair and later said, "My machines came from too far away."
Less than a year later, Feynman had his triumph. At an American Physical Society meeting in New York, Murray Slotnick talked about some calculations he had done with two different meson-nucleon couplings. He had shown that these two couplings indeed gave different answers. After Slotnick's talk, Oppenheimer got up from the audience and said that Slotnick's calculations must be wrong since they violated Case's Theorem. Poor Slotnick had to confess that he had never heard of Case's Theorem and Oppenheimer informed him that he could remedy his ignorance by listening to Professor Case present his theorem the following day.
That night, Feynman couldn't sleep so he decided to re-do Slotnick's calculations by using his diagram techniques. The next day at the conference, Feynman sought out Slotnick, told him what he had done, and suggested they compare results. "What do you mean you worked it out last night?" Slotnick responded. "It took me six months!" As the two compared answers, Slotnick asked, "What is that Q in there, that variable Q?" Feynman replied that the Q was the momentum transfer as the electron was deflected by different angles. "Oh," Slotnick replied. "I only have the limiting value as Q approaches zero. For forward scattering." Feynman said, "No problem, we can just set Q equal to zero in my formulas!" Feynman found that he had obtained the same answer as Slotnick.
After Case had presented his theorem, Feynman stood up at the back of the audience and said, "Professor Case, I checked Slotnick's calculations last night and I agree with him, so your theorem must be wrong." And then he sat down. That was a thrilling moment for Feynman, like winning the Nobel Prize—which he did much later—because he was now sure that he had achieved something significant. It had taken Slotnick six months to do the case of zero momentum transfer while Feynman had been able to complete the calculation for arbitrary momentum transfer in one evening. The computational toolkit that we now call Feynman Diagrams have now penetrated to almost all areas of physics and his diagrams appear on the blackboards of physicists all around the world. This toolkit is undoubtedly Feynman's greatest gift to physics and the story perfectly illustrates Feynman's preference for concrete, detailed calculation rather than reliance on more abstract theorems.
The Physics of Computation
At the invitation of his friend Ed Fredkin, Feynman delivered a keynote lecture at "The Physics of Computation" Conference at MIT in 1981. Feynman considered the problem of whether it was possible to perform an accurate simulation of Nature on a classical computer. As Nature ultimately obeys the laws of quantum mechanics, the problem reduces to simulating a quantum mechanical system on a classical computer. Because of the nature of quantum objects like electrons, truly quantum mechanical calculations on a classical computer rapidly become impractical for more than a few 10's of electrons.
Feynman then proceeded to consider a new type of computer based on quantum mechanics: a quantum computer. He realized that this was a new type of computer: "Not a Turing machine, but a machine of a different kind." Interestingly, Feynman did not go on to explore the different capabilities of quantum computers but simply demonstrated how you could use them to simulate true quantum systems.
By his presence at the conference, Feynman stimulated interest both in the physics of computation and in quantum computing. At this conference 30 years later, we heard several talks summarizing progress towards actually building a quantum computer. In the last five years of his life, Feynman gave lectures on computation at Caltech, initially with colleagues Carver Mead and John Hopfield, and for the last three years by himself.
I was fortunate enough to be asked by Feynman to write up his "Lectures on Computation." The lectures were a veritable tour de force and were probably a decade ahead of their time. Feynman considered the limits to computation due to mathematics, thermodynamics, noise, silicon engineering, and quantum mechanics. In the lectures, he also gave his view about the field of computer science: He regarded science as the study of natural systems and classified computer science as engineering since it studied man-made systems.
Inspiring Later Generations
Feynman said that he started out very focused on physics and only broadened his studies later in life. There are several fascinating biographies of Feynman but the one I like best is No Ordinary Genius by Christopher Sykes. This is a wonderful collection of anecdotes, interview, and articles about Feynman and his wide range of interests—from physics, to painting, to bongo drums and the Challenger Enquiry. Feynman was a wonderful inspiration to the entire scientific community and his enjoyment of and enthusiasm for physics is beautifully captured in the TV interview, "The Pleasure of Finding Things Out," produced by Christopher Sykes for the BBC. Feynman is forever a reminder that we must try to think differently in order to innovate and succeed.
—Tony Hey, corporate vice president of the External Research Division of Microsoft Research


||It has been suggested that Josephson energy be merged into this article. (Discuss) Proposed since January 2013.|
The Josephson effect is the phenomenon of supercurrent—i.e. a current that flows indefinitely long without any voltage applied—across a device known as a Josephson junction (JJ), which consists of two superconductors coupled by a weak link. The weak link can consist of a thin insulating barrier (known as a superconductor–insulator–superconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivity at the point of contact (S-s-S).
The Josephson effect is an example of a macroscopic quantum phenomenon. It is named after the British physicist Brian David Josephson, who predicted in 1962 the mathematical relationships for the current and voltage across the weak link. The DC Josephson effect had been seen in experiments prior to 1962, but had been attributed to "super-shorts" or breaches in the insulating barrier leading to the direct conduction of electrons between the superconductors. The first paper to claim the discovery of Josephson's effect, and to make the requisite experimental checks, was that of Philip Anderson and John Rowell. These authors were awarded patents on the effects that were never enforced, but never challenged.
Before Josephson's prediction, it was only known that normal (i.e. non-superconducting) electrons can flow through an insulating barrier, by means of quantum tunneling. Josephson was the first to predict the tunneling of superconducting Cooper pairs. For this work, Josephson received the Nobel prize in physics in 1973. Josephson junctions have important applications in quantum-mechanical circuits, such as SQUIDs, superconducting qubits, and RSFQ digital electronics.
The basic equations governing the dynamics of the Josephson effect are
- (superconducting phase evolution equation)
- (Josephson or weak-link current-phase relation)
where U(t) and I(t) are the voltage and current across the Josephson junction, is the "phase difference" across the junction (i.e., the difference in phase factor, or equivalently, argument, between the Ginzburg–Landau complex order parameter of the two superconductors composing the junction), and Ic is a constant, the critical current of the junction. The critical current is an important phenomenological parameter of the device that can be affected by temperature as well as by an applied magnetic field. The physical constant is the magnetic flux quantum, the inverse of which is the Josephson constant.
The three main effects predicted by Josephson follow from these relations:
- The DC Josephson effect
- This refers to the phenomenon of a direct current crossing from the insulator in the absence of any external electromagnetic field, owing to tunneling. This DC Josephson current is proportional to the sine of the phase difference across the insulator, and may take values between and .
- The AC Josephson effect
- With a fixed voltage across the junctions, the phase will vary linearly with time and the current will be an AC current with amplitude and frequency . The complete expression for the current drive becomes . This means a Josephson junction can act as a perfect voltage-to-frequency converter.
- The inverse AC Josephson effect
- If the phase takes the form , the voltage and current will be
The DC components will then be
Hence, for distinct AC voltages, the junction may carry a DC current and the junction acts like a perfect frequency-to-voltage converter.
The Josephson effect has found wide usage, for example in the following areas:
- SQUIDs, or superconducting quantum interference devices, are very sensitive magnetometers that operate via the Josephson effect. They are widely used in science and engineering.
- In precision metrology, the Josephson effect provides an exactly reproducible conversion between frequency and voltage. Since the frequency is already defined precisely and practically by the caesium standard, the Josephson effect is used, for most practical purposes, to give the definition of a volt (although, as of July 2007, this is not the official BIPM definition).
- Single-electron transistors are often constructed of superconducting materials, allowing use to be made of the Josephson effect to achieve novel effects. The resulting device is called a "superconducting single-electron transistor." The Josephson effect is also used for the most precise measurements of elementary charge in terms of the Josephson constant and von Klitzing constant which is related to the quantum Hall effect.
- RSFQ digital electronics is based on shunted Josephson junctions. In this case, the junction switching event is associated to the emission of one magnetic flux quantum that carries the digital information: the absence of switching is equivalent to 0, while one switching event carries a 1.
- Josephson junctions are integral in superconducting quantum computing as qubits such as in a flux qubit or others schemes where the phase and charge act as the conjugate variables.
- Superconducting tunnel junction detectors (STJs) may become a viable replacement for CCDs (charge-coupled devices) for use in astronomy and astrophysics in a few years. These devices are effective across a wide spectrum from ultraviolet to infrared, and also in x-rays. The technology has been tried out on the William Herschel Telescope in the SCAM instrument.
- Quiterons and similar superconducting switching devices.
- Josephson effect has also been observed in SHeQUIDs, the superfluid helium analog of a dc-SQUID.
|Wikimedia Commons has media related to Josephson effect.|
- Andreev reflection
- Fractional vortices
- Ginzburg–Landau theory
- Macroscopic quantum phenomena
- Macroscopic quantum self-trapping
- Pi Josephson junction
- Varphi Josephson junction
- Quantum computer
- Quantum gyroscope
- Rapid single flux quantum (RSFQ)
- Superconducting tunnel junction
- Zero-point energy
- Josephson, B. D., "Possible new effects in superconductive tunnelling," Physics Letters 1, 251 (1962) doi:10.1016/0031-9163(62)91369-0
- Josephson, B. D. (1974). "The discovery of tunnelling supercurrents". Rev. Mod. Phys. 46 (2): 251–254. Bibcode:1974RvMP...46..251J. doi:10.1103/RevModPhys.46.251.
- Josephson, Brian D. (December 12, 1973). "The Discovery of Tunneling Supercurrents (Nobel Lecture)".
- Anderson, P W; Rowell, J M (1963). "Probable Observation of the Josephson Tunnel Effect". Phys. Rev. Letters 10: 230. Bibcode:1963PhRvL..10..230A. doi:10.1103/PhysRevLett.10.230.
- The Nobel prize in physics 1973, accessed 8-18-11
- Anderson, P. W., and Dayem, A. H., "Radio-frequency effects in superconducting thin film bridges," Physical Review Letters 13, 195 (1964), doi:10.1103/PhysRevLett.13.195
- Dawe, Richard (28 October 1998). "SQUIDs: A Technical Report - Part 3: SQUIDs" (website). http://rich.phekda.org. Retrieved 2011-04-21.
- Barone, A.; Paterno, G. (1982). Physics and Applications of the Josephson Effect. New York: John Wiley & Sons. ISBN 0-471-01469-9.
- International Bureau of Weights and Measures (BIPM), SI brochure, section 2.1, accessed 4-17-12
- Fulton, T.A.; et al. (1989). "Observation of Combined Josephson and Charging Effects in Small Tunnel Junction Circuits". Physical Review Letters 63 (12): 1307–1310. Bibcode:1989PhRvL..63.1307F. doi:10.1103/PhysRevLett.63.1307. PMID 10040529.
- Bouchiat, V.; Vion, D.; Joyez, P.; Esteve, D.; Devoret, M. H. (1998). "Quantum coherence with a single Cooper pair". Physica Scripta T 76: 165. Bibcode:1998PhST...76..165B. doi:10.1238/Physica.Topical.076a00165.
- Physics Today, Superfluid helium interferometers, Y. Sato and R. Packard, October 2012, page 31


Technology Research News
Give an electron two paths to get to one
location and it will usually take both. This fact of quantum physics plays
a leading role in a computer architecture that could replace today's chip
technology when it reaches its limits in a decade or so.
According to the laws of quantum physics, electrons are waves as well
as particles. Like ocean waves, where two crests meet they reinforce each
other and where a crest and trough meet they cancel each other out. Researchers
at University of Missouri at Rolla have devised a scheme for using electron
wave interference to represent the ones and zeros of digital
Traditional electronic computers use combinations of transistors, which
are tiny electronic switches, as the logic units that perform the binary
arithmetic at the heart of digital computing. Electron wave computers
would use networks of microscopic wire rings that form the two paths for
the electron waves to follow, said Cheng-Hsiao Wu, a professor of electrical
and computer engineering at the University of Missouri at Rolla.
"You do not need transistors to control the flow of charge if all the
devices involved are very small and at low temperature," said Wu.
The researchers' proposal involves using modified forms of Aharonov-Bohm
rings, which are used in basic physics research, to form the logic gates
of computers. Aharonov-Bohm rings are circles of extremely thin wire and
are commonly made several times smaller than a red blood cell. Due to
their wave nature, electrons entering the Aharonov-Bohm rings travel in
both directions at once, meeting -- and reinforcing each other -- at the
Using a magnetic field perpendicular to the ring, researchers can speed
up or slow down the electron wave traveling in one side of the ring, throwing
the waves in the two sides out of sync and causing the waves to cancel
each other out when they meet at the other end. The reinforced waves and
the canceled waves could represent the ones and zeros of computing, according
Aharonov-Bohm rings have an input and an output terminal. The researchers'
scheme calls for making three- and four-terminal Aharonov-Bohm rings.
Their work shows that three-terminal rings could be combined to form IF-THEN,
XOR, OR, AND and INVERTER logic units. These logic units could, in turn,
be combined to form half adders and full adders. A half adder adds two
binary numbers but cannot carry, and a full adder includes the carry function.
A single, four-terminal Aharonov-Bohm ring could also be used as a half
adder, said Wu. "It replaces eight transistors for the same function."
And two connected four-terminal Aharonov-Bohm rings could serve as a full
adder. "This replaces about two dozen transistors in traditional microelectronic
circuits," he said.
In addition to the potential for making smaller, and therefore faster,
computer circuits, electron wave computers could solve certain problems
faster than even the fastest ordinary computer by examining all of the
possible solutions to a problem at once, according to Wu.
Electron wave interference could be used to make massively parallel processing
computers, he said. "Millions of inputs enter a large network [of rings]
simultaneously with desirable outputs when the waves arrive at the output
terminals. This is similar to optical computing."
Optical computers use light waves that reinforce and cancel each other
out. Last year, researchers at the University of Rochester demonstrated
an optical computer running a quantum search algorithm.
The electron wave scheme is an idea worth trying, said Ian Walmsley, a
professor of experimental physics at the University of Oxford and a professor
of optics at the University of Rochester. "The nice thing about electrons
is that [their] wavelengths are inherently smaller than optical wavelengths,
so the whole machine can be smaller. At present I see the advance as a
technical one rather than a fundamental one," he added.
"It's a very neat idea but... completely theoretical," said Mike Lea,
a professor of physics at the University of London. "I'd be quite skeptical
about claims without at least some analysis of the likely practicalities
based on real experiments," he said.
The researchers are working out the physics for larger networks of Aharonov-Bohm
rings, said Wu. "I would like to convince experimentalists elsewhere to
simply extend the original Aharonov-Bohm effect to three or four terminals.
I promise nice results will come out of such a simple extension," he said.
Given that today's semiconductor technology is likely to reach its limits
by the year 2015, researchers and engineers should have a good idea of
how to build devices smaller than 10 nanometers by then, said Wu. At that
point, electron wave computing could be a contender for the next generation
computer architecture, he said.
Wu's research colleague was Diwakar Ramamurthy. They published the research
in the February 15, 2002 issue of the journal Physical Review B. The research
was funded by the university.
Timeline: 13 years
TRN Categories: Quantum Computing and Communications; Integrated
Story Type: News
Related Elements: Technical paper, "Logic Functions from
Three-Terminal Quantum Resistor Networks for Electron Wave Computing,"
Physical Review B, February 15, 2002
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Introduced in Alan Turing
's 1936 paper On computable numbers, with an application to the Entscheidungsproblem
, a universal Turing machine is a mathematical idealisation of a general purpose computer
. Able to act, with appropriate input, as literally any
other possible Turing Machine
, Turing's invention, essentially the concept of a general purpose cpu
executing a stored program
, was probably the largest single step taken in the development of the computer, and is often regarded as the start of computer science
A Turing machine (TM) consists of a tape, a head which can mark and erase the tape, and a set of states. Depending on whether the tape is currently marked, and which state is occupied, the TM will erase or mark the tape or not, and move it one square left or right, at which point the next state kicks in.
Additionally, there is a state which causes the TM to halt, if it is reached.
The tape is considered to be of arbitrary length and composed of discrete units which are accessible to the head in strict order, singly and wholly - that is the tape is an idealised one-bit erasable paper tape which never stretches, breaks, folds, runs out, or breaks other rules which are harder to think of.
The critical thing is that though the tape may be arbitrarily large, each step of the operation of a TM is completely determined by a finite number of simple and unambiguous rules. It is completely mechanical in its operation, and always behaves in the same way for any particular state and input.
These rules defining a TM (the set of states) can be written out in a standard form as marks on a tape. The interpretation of such an on-tape representation of a TM is then a mechanical procedure which can be realised by some TM with a suitable set of states.
A universal Turing machine (UTM) is a particular TM so constructed that its tape can encode any TM whatsoever, with the guarantee that the UTM will then do just what the encoded TM would do.
Suppose we have a machine M, then its output with initial tape t can be written M(t). Then a UTM U is a TM such that:
for all outputs Mi(tj) there's some ei,j such that U(ei,j) = Mi(tj)
We'd call ei,j the encoding of Mi(tj).
It's also required that the UTM can recognise input that is not a valid encoding of a TM and produce a predetermined response when this occurs.
Turing proved the existence of such UTM's by specifying one in his paper - it turned out not to be very complex - and showing it had the characteristic required, of replicating the behaviour of an arbitrary TM which is encoded on its tape. This is the essence of the modern computer, that given sufficient storage it can carry out an arbitrary program, encoded into some specific "language". The choice of a particular UTM defines a particular language.
Turing's insight was that an algorithm, when encoded, is just so much data that can then be operated on by another algorithm. The idea of encoding a TM as input for execution by a UTM is pretty much all you need for the general idea of a computer program.
The fact that a UTM can emulate any TM at all makes it easy to establish fundamental equivalences between various computational methods. If a particular method can produce a UTM, then it's obvious it can compute anything computable by an arbitrary TM. Such a formalism or language is said to be Turing complete. Specifications for UTM's have been written in formalisms as diverse as XSLT, sendmail.cf and cellular automata such as Conway's game of life.
This property of universality shifts the competition from what can be computed to the number of steps and amount of input required. No matter how featureful, elegant and concise the programming language you construct, whatever computations it can perform can be done in sendmail.cf or brainfuck.
Universality has been of interest to some heterodox physicists, such as Ed Fredkin and Steven Wolfram. Fredkin, on a suggestion of Feynman's, has been investigating the possibility of using cellular automata as a physics model and suggests suitable automata must be both universal (i.e. Turing complete) and reversible. Wolfram (also big on CA) sees in the UTM an upper bound to the complexity of the makeup of the universe. David Deutsch has proposed that "every finitely realizable physical system can be perfectly simulated by a universal model computing machine operating by finite means", and has attempted to extend the idea of a UTM to quantum computing.
Mathematician Gregory Chaitin has used the UTM as a building block in his algorithmic information theory, refining the notion by specifying that the encoding for the TM's must instruct the UTM how long they are (Chaitin says they are 'self-delimiting') and using them to define the algorithmic complexity of a string relative to a given UTM - the length of the shortest input that will cause the UTM to output that string - and to formulate his bizarre constant Omega - the probability, for some self-delimiting UTM, that it will halt with random input. Chaitin imagines flipping a coin to determine the state of each successive bit of the unread tape, as the UTM reads in its program. It's required to be self-delimiting so that the UTM knows when to stop reading and Chaitin knows when to stop flipping coins.
Gregory Chaitin, Foundations of Mathematics at:
For Fredkin, see:


Rise of the Boson-Sampling Computer
OXFORD, England, and ST. LUCIA, Australia, Jan. 2, 2013 — Despite the widespread research on quantum computing, nobody has built a machine that uses quantum mechanics to solve a computational problem faster than a classical silicon-based computer. Now scientists from universities in England and Australia have developed device called a boson sampling computer that rivals a quantum computer.
Although boson sampling computers are not believed to have all the problem solving ability of a full quantum computer, they can solve some problems faster than today’s machines, and can be much easier to build experimentally with existing photonic technology. The device could pave the way to larger devices that could offer the first definitive quantum-enhanced computation.
Boson sampling requires three main ingredients: single bosons, the large-scale linear manipulation of bosons, and single-boson-sensitive detectors.
The 8-cm-long silica-on-silicon photonic chip in the center of the picture served as the four-photon quantum boson sampling machine. Arrays of single-mode fibers are glued to the left and right sides of the chip. For viewing purposes, a red laser is coupled into two of the single-mode fibers (right side of picture), which illuminate a portion of the on-chip interferometric network. For the boson sampling experiment, the red laser was replaced with single-photon sources. There are five thermal phase shifting elements on top of the chip, although they were not used in this experiment. This image relates to the paper by Dr. Justin Spring and colleagues. Courtesy of Dr. James C. Gates.
Photons are identical at a fundamental level, exhibiting a strong quantum level of entanglement. If two sufficiently identical photons come together, they behave in a connected way — almost as if they clump together. When scaled up to multiple input photons, these entanglements cause the outputs of a boson-sampling circuit to clump together in a characteristic way, predictable by quantum mechanics but difficult to calculate using conventional computers.
In their experiment, Oxford University’s Justin Spring and colleagues used single photons and quantum interference to perform a calculation that is believed to be very difficult on a classical computer.
“Boson sampling provides a model of quantum-enhanced computation that is experimentally feasible with existing photonic technology,” Spring said. “Future generations of boson sampling machines will benefit from ongoing advances in integrated photonics.”
The experiment was performed on a photonic chip developed by professor Peter Smith and Dr. James Gates from the Optoelectronics Research Center at the University of Southampton.
The logo of the Quantum Technology Lab spelled out with the laser beams used in the BosonSampling device. This image relates to the paper by Dr. Matthew Broome and colleagues. Courtesy of Alisha Toft.
“The chip offers a scalable route … to build large linear systems required for larger boson sampling machines,” Gates said. “If one is going to eventually need to move ‘on chip’ with more complex boson sampling machines, there is obvious benefit in building the proof-of-principle devices ‘on chip’ as well. The move to optical processing on a chip format can be likened to the shift to integrated silicon chips in electronics.”
In a separate experiment, Dr. Matthew Broome and colleagues at the University of Queensland built a device they called BosonSampling to determine whether quantum computers are the only way to perform efficient computations, or whether conventional computers can solve the problem almost as quickly. The device implemented a form of quantum computation where a handful of single photons were sent through a photonic network and then researchers sampled how often they exited the network outputs.
“Although this sounds simple, for large devices and many photons, it becomes extremely difficult to predict the outcomes using a conventional computer, whereas our measurements remain straightforward to do,” Broome said.
The device — proposed in late 2010 by associate professor Scott Aaronson and Dr. Alex Arkhipov of MIT — will provide strong evidence that quantum computers do indeed have an exponential advantage over conventional computers.
Dr. Matthew Broome at work on the BosonSampling device. This image relates to the paper he wrote in collaboration with colleagues. Courtesy of Alisha Toft.
“Scott and Alex’s proposal was a 94-page mathematical tour de force,” said experimental team leader Andrew White of the University of Queensland. “We genuinely didn’t know if it would implement nicely in the lab, where we have to worry about real-world effects like lossy circuits, and imperfect single photon sources and detectors.”
The BosonSampling device behaves as expected, paving the way for larger and larger instances of this experiment. The prediction is that, with just tens of photons, it can outperform any of today’s supercomputers.
“The first proof-of-principle demonstrations of BosonSampling have been shown — even if only with three photons, rather than the 30 or so required to outperform a classical computer,” Aaronson said. “I did not expect this to happen so quickly.”
The studies appeared in Science
) and (doi: 10.1126/science.1231440
For more information, visit: www.ox.ac.uk


Scientists Score New Victory Over Quantum Uncertainty
ScienceDaily (Feb. 26, 2012) — Most people attempt to reduce the little uncertainties of life by carrying umbrellas on cloudy days, purchasing automobile insurance or hiring inspectors to evaluate homes they might consider purchasing. For scientists, reducing uncertainty is a no less important goal, though in the weird realm of quantum physics, the term has a more specific meaning.
For scientists working in quantum physics, the Heisenberg Uncertainty Principle says that measurements of properties such as the momentum of an object and its exact position cannot be simultaneously specified with arbitrary accuracy. As a result, there must be some uncertainty in either the exact position of the object, or its exact momentum. The amount of uncertainty can be determined, and is often represented graphically by a circle showing the area within which the measurement actually lies.
Over the past few decades, scientists have learned to cheat a bit on the Uncertainty Principle through a process called "squeezing," which has the effect of changing how the uncertainty is shown graphically. Changing the circle to an ellipse and ultimately to almost a line allows one component of the complementary measurements -- the momentum or the position, in the case of an object -- to be specified more precisely than would otherwise be possible. The actual area of uncertainty remains unchanged, but is represented by a different shape that serves to improve accuracy in measuring one property.
This squeezing has been done in measuring properties of photons and atoms, and can be important to certain high-precision measurements needed by atomic clocks and the magnetometers used to create magnetic resonance imaging views of structures deep inside the body. For the military, squeezing more accuracy could improve the detection of enemy submarines attempting to hide underwater or improve the accuracy of atom-based inertial guidance instruments.
Now physicists at the Georgia Institute of Technology have added another measurement to the list of those that can be squeezed. In a paper appearing online February 26 in the journal Nature Physics, they report squeezing a property called the nematic tensor, which is used to describe the rubidium atoms in Bose-Einstein condensates, a unique form of matter in which all atoms have the same quantum state. The research was sponsored by the National Science Foundation (NSF).
"What is new about our work is that we have probably achieved the highest level of atom squeezing reported so far, and the more squeezing you get, the better," said Michael Chapman, a professor in Georgia Tech's School of Physics. "We are also squeezing something other than what people have squeezed before."
Scientists have been squeezing the spin states of atoms for 15 years, but only for atoms that have just two relevant quantum states -- known as spin ½ systems. In collections of those atoms, the spin states of the individual atoms can be added together to get a collective angular momentum that describes the entire system of atoms.
In the Bose-Einstein condensate atoms being studied by Chapman's group, the atoms have three quantum states, and their collective spin totals zero -- not very helpful for describing systems. So Chapman and graduate students Chris Hamley, Corey Gerving, Thai Hoang and Eva Bookjans learned to squeeze a more complex measure that describes their system of spin 1 atoms: nematic tensor, also known as quadrupole.
Nematicity is a measure of alignment that is important in describing liquid crystals, exotic magnetic materials and some high temperature superconductors.
"We don't have a spin vector pointing in a particular direction, but there is still some residual information in where this collection of atoms is pointing," Chapman explained. "That next higher-order description is the quadrupole, or nematic tensor. Squeezing this actually works quite well, and we get a large degree of improvement, so we think it is relatively promising."
Experimentally, the squeezing is created by entangling some of the atoms, which takes away their independence. Chapman's group accomplishes this by colliding atoms in their ensemble of some 40,000 rubidium atoms.
"After they collide, the state of one atom is connected to that of the other atom, so they have been entangled in that way," he said. "This entanglement creates the squeezing."
Reducing uncertainty in measuring atoms could have important implications for precise magnetic measurements. The next step will be to determine experimentally if the technique can improve the measurement of magnetic field, which could have important applications.
"In principle, this should be a straightforward experiment, but it turns out that the biggest challenge is that magnetic fields in the laboratory fluctuate due to environmental factors such as the effects of devices such as computer monitors," Chapman said. "If we had a noiseless laboratory, we could measure the magnetic field both with and without squeezed states to demonstrate the enhanced precision. But in our current lab environment, our measurements would be affected by outside noise, not the limitations of the atomic sensors we are using."
The new squeezed property could also have application to quantum information systems, which can store information in the spin of atoms and their nematic tensor.
"There are a lot of things you can do with quantum entanglement, and improving the accuracy of measurements is one of them," Chapman added. "We still have to obey Heisenberg's Uncertainty Principle, but we do have the ability to manipulate it."
Hamley, C. D., C. S. Gerving, et al. (2012). "Spin-nematic squeezed vacuum in a quantum gas." Nat Phys advance online publication.
The standard quantum limit of measurement uncertainty can be surpassed using squeezed states, which minimize the uncertainty product in Heisenberg’s relation by reducing the uncertainty of one property at the expense of another1. Collisions in ultracold atomic gases have been used to induce quadrature spin squeezing in two-component Bose condensates 2, 3, for which the complementary properties are the components of the total spin vector. Here, we generalize this finding to a higher-dimensional spin space by measuring squeezing in a spin-1 Bose condensate. Following a quench through a quantum phase transition, we demonstrate that spin-nematic quadrature squeezing improves on the standard quantum limit by up to 8–10 dB—a significant increase on previous measurements. This squeezing is associated with negligible occupation of the squeezed modes, and is analogous to optical two-mode vacuum squeezing. The observation has implications for continuous variable quantum information and quantum-enhanced magnetometry.
Delenda est Carthago


A research team from the Institut CatalÓ de Nanotecnologia (ICN), in Barcelona, has demonstrated a device that induces electron spin motion without net electric currents, a key step in developing the spin computers of the future. The results are published in the Dec 17 issue of the journal Science. The authors are Marius V. Costache and Sergio O. Valenzuela, an ICREA Professor who is leader of the Physics and Engineering of Nanodevices Group at ICN.
Spintronics is a branch of electronics that aims to use the electron spin rather than its charge to transport and store information. The electron spin comes in two forms, "spin up" or "spin down", and would allow significantly more data to be stored and analyzed than is possible with current electronics. Moreover, spin computers would be able to process vast amounts of information while using less energy and generating much less heat than conventional computers.
Advances in spintronics have already impacted commercial products, enabling a huge increase in storage capacity of magnetic hard disks. However, the devices comprise ferromagnetic multilayers that act as spin filters and require conventional electrical charge currents in order to work. To garner the full potential of spintronics, further fundamental advances are urgently needed.
Researchers working in this field face a key challenge: how to generate and control spins without the simultaneous generation of electric current, and the resultant energy losses? This would enable not just data storage, but calculations to be realized directly using spin states.
As reported in the journal Science, Prof. Valenzuela and Dr. Costache have proposed and experimentally demonstrated a ratchet concept to control the spin motion. In analogy to a ratchet wrench, which provides uniform rotation from oscillatory motion, such ratchets achieve directed spin transport in one direction, in the presence of an oscillating signal. Most important, this signal could be an oscillatory current that results from environmental charge noise; thus future devices based on this concept could function by gathering energy from the environment.
The efficiency of the ratchet can be very high. Reported results show electron polarizations of the order of 50%, but they could easily exceed 90% with device design improvements. The spin ratchet, which relies on a single electron transistor with a superconducting island and normal metal leads, is able to discriminate the electron spin, one electron at a time. The devices can also function in a "diode" regime that resolves spin with nearly 100% efficacy and, given that they work at the single-electron level, they could be utilized to address fundamental questions of quantum mechanics in the solid state or to help prepare the path for ultrapowerful quantum or spin computers.
The main drawback of the devices is that they work at low temperature. However, this does not represent a problem for quantum computing applications as solid state implementations of quantum computers will most likely require similar working conditions. Future research at the ICN will focus on increasing the spin ratchet efficiency and testing different ratchet protocols to implement a working device at room temperature.
CATALAN INSTITUTE OF NANOTECHNOLOGY (ICN)
The Catalan Institute of Nanotechnology (ICN) is a private foundation created in 2003 and forms part of CERCA, the Network of Research Centers launched by the Catalan Government as a key plank of the long-term strategy to foster the development of a knowledge-based economy. The ICN┤s multicultural team of scientists, representing over 20 nationalities, aims to produce cutting-edge science and develop next-generation technologies by investigating the new properties of matter that arise from the fascinating behavior at the nanoscale.
Research is devoted on one side to the study and understanding of fundamental physical phenomena associated to state variables (electrons, spin, phonons, photons, plasmons, etc.), the investigation of new properties derived from tailored nanostructures, and the opening of new routes and fabrication processes for the conception of new nanodevices.
On the other side, researchers also explore the state of aggregation at the nanometric scale, the development of nanoproduction methods, synthesis, analysis, and manipulation of aggregates and structures of nanometric dimension, and the development of techniques for characterizing and manipulating nanostructures.
These lead to commercially relevant studies such as the functionalization of nanoparticles, the encapsulation of active agents, novel drugs and vaccines, new nanodevices and nanosensors, with applications in health, food, energy, environment, etc.
The Institute actively promotes collaboration among scientists from diverse areas of specialization (physics, chemistry, biology, engineering), and trains new generations of scientists, offering studentships, doctoral and post-doctoral positions.
Institut Catala de Nanotecnologia
Tel: +(34) 93 581 4408, Email: firstname.lastname@example.org, Web: www.icn.cat
Communicacion Dept.: Ana de la Osa, email@example.com
Principal Researcher: ICREA Prof. Dr. Sergio Valenzuela, SOV@icrea.cat
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.


Speed of light
From CreationWiki, the encyclopedia of creation science
The speed of light in vacuum is held to be constant at 299,792,458 m/s (186,282.397 miles per second). Designated by the symbol "c" (for "constant"), it is a fundamental quantity of the universe. According to special relativity it is the universe's speed limit and it is part of the relation between mass and energy:
Some have proposed that the speed of light has decayed since the Creation. While this theory opened the door to scientific solutions to the distant starlight problem, it is not generally accepted by creation scientists.
One-Way Speed of Light
Sagnac proved that light travels at different speeds depending on its direction and its proximity to the center of Earth's gravity, lending weight to the Anisotropic convention.
The one-way speed of light has never been measured. Every known measurement of the speed of light includes reflecting it from another surface. This necessarily changes the nature of light, as it can only be the average of the outbound and inbound leg. Additionally, all electronic means to measure the speed of light cannot themselves operate at the speed of light. This introduces error and constraint into the measurement. If we attempt to embed a signal into a light beam to synchronize two clocks at a distance, the time it takes to both create and to interpret the signal introduce another constraint. In fact, any introduction of a measurement mechanism necessarily constrains the measurement because no measurement mechanism can operate at the speed of light.
Einstein understood the primary paradox of the speed of light, as evidenced by the theory of black holes. A black hole's gravity is so strong that light cannot reach escape velocity. However, gravity can only act in this manner between bodies with mass, which necessarily means that photons have mass. Physicists generally do not accept the notion that photons have mass. If they do not, they would be able to escape a black hole, and it would not be black after all. However, if the photon has mass, then it is a particle with mass traveling at the speed of light. For such particles, time stands still. There is no duration between their departure (from an emitting source) and their destination. Essentially departure and arrival are instantaneous. If this is the case with a photon, then there is no such thing as a light-year in space, and the age of the Cosmos cannot be determined using light as a basis. Moreover, the speed of light is a function of distance and duration: speed = distance/time. However, Einstein asserted that time is relative. If this is true then the speed of light is also relative and cannot be constant.
To resolve this paradox, Einstein side-stepped it by stipulating that the speed of light is constant without ever proving it.
That light requires the same time to traverse the path A > M as for the path B > M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity" (Einstein 1961, p. 23) [emphasis is in the original].
Whenever scientists encounter particle behaviors that defy the speed of light, such as the propensity of particles to instantly share behaviors even across vast distances (e.g. Quantum Entanglement) they still hold to the notion that the speed of light is constant, eliciting the strangest explanations, including the idea that all particles in the universe are connected to all other particles through wormholes. Such oddball theories are the simplest evidence that the "constant" speed of light has been accepted as a reality rather than a stipulation for mathematical purposes.
Albert A. Michelson is credited with developing the method for the definitive measurement of the speed of light. In 1902 he published his classic paper on the speed of light, and in 1907 was awarded the Nobel Prize in Physics for this work. Michelson also proposed the standardization of the international unit of length, the meter, using specified wavelengths of light rather than an artifact. For decades the scientific community used Michelson's standardization method, but finally decided to define the SI unit of length according to the speed of light. Today one meter is defined as exactly 1/299,792,458 of the distance that a beam of light travels in one second.
Many scientists in the past have speculated about possible changes in the values of one or more physical constants and its implications. These speculations were not always greeted with enthusiasm from the scientific community because the implications of any variation in any constant are enormous: it would introduce changes at astronomical levels in the very fiber of the Universe. Yet the idea never totally died out and was never totally suppressed.
Glenn Morton was one of the first persons to put forth a concrete and testable model. He started not from changing fundamental constants, but from another angle. Soon Barry Setterfield came forward with his proposal of variation in the velocity of light. His initial proposal went through several revisions and modifications and creationist publications quoted him widely. Some secular publications also used the information, but the general response was to resist his proposals.
Johnson C. Philip from India put forth the same idea in a broader way in 1982 and did some work with the Physics department of Jiwaji University in India. However, he had to abandon the work in 1984 due to the resistance of some non creationist professors.
The proposal remains promising, and much work can be done. The resistance remains, especially from non creationists. However, the topic might find a revival, now that the secular community has started to consider the idea of changing fundamental constants.
The speed of light has been used to calculate the distance of supernova 1987A from earth with great accuracy, based on observing the time taken for its light to illuminate the Large Magellanic Cloud. It is the standard method for calculating the distance to nearby galaxies.
The part of the SN1987A ring perpendicular to the explosion center (as seen from us) was observed to light up about 8 months after the explosion. The light that took a detour via the ring to us was always a ring radius behind the direct light regardless of the speed of light that prevailed during the trip. The ring radius could be calculated to these 8 months times the speed of light as applied to the year 1987, when the measurement was made. Thus it is not of this observation to deduce if the light has had any different speed before 1987.
The notion of c-decay is currently out of favor even among creationists. Two models for the creation of the universe, i.e. white hole cosmology and cosmological relativity, both assume a constant value of c.
The Anisotropic Synchrony Convention holds for a variable value for c, and likewise provides for c to be relative to the speed of the emitting object. Anisotropism is the actual de-facto convention for Scripture, as God describes things from a human's-eye point-of-view. Even Christ said he would use earthly things to describe heavenly things. The human point-of-view is integrated to the Anisotropic convention, providing for the instantaneous arrival of distant starlight as well as explain local measurement in terms of time dilation.
- Biography of Albert A. Michelson from the Nobel Committee
- An Alternate View of SN1987A by Selva Harris.
- Speed of light may have changed recently by Eugenie Samuel Reich, NewScientist.com


Portland, Ore. - In the search for a physical system that could encode quantum states and thus form the basis for a practical quantum computer, researchers at the University of Michigan and the University of Rochester are turning to photonics.
Photons, like electrons, are quantum particles and can be manipulated with optical devices. By making use of semiconductor structures such as acousto-optic modulators or quantum wells, photons can modify the quantum states of electrons.
In a recent experiment at the University of Michigan, researchers used a magnetic semiconductor material that confined electrons in a quantum well. Subsequently lasing the well with ultrafast pulses entangled the electrons' spin states. Entanglement is the fundamental basis for quantum computing.
"After studying the results of others who have tried all kinds of different approaches to controlling qubits [quantum bits], we found a method based on semiconductor technology that, when combined with advances in nanotechnology, we think holds great promise for practical implementations," said professor Roberto Merlin, a physicist on the project at the university's Optical Physics Interdisciplinary Laboratory.
Another project, at the University of Rochester's Center for Quantum Information, is using methods based on nonlinear optical waveguides to investigate both quantum entanglement between photons and more conventional physics based on photon interference. The work, led by Ian Walmsley, a physicist specializing in ultrafast phenomena, has seen some success on both fronts.
Though not a pure quantum-state operation, photon interference has turned out to be useful in decoding quantum states and might serve as a practical I/O method for a quantum pro-cessor, the Rochester team reports. In addition, the optical interference techniques developed at the lab could be applied to quantum communications over optical fibers, an area that has recently spawned an actual prototype of a secure communications system based on quantum principles.
The Rochester team has developed a new type of high-brightness optical source that achieves tight control of a photon's wavefunction inside of an optical waveguide. The physical technique is to use phase matching to control two-photon interactions. Confining the photons in the waveguide cavity has allowed the researchers to first entangle and then disentangle photon states.
While these experiments have been successful in generating two pairs of entangled photons, the problem facing the researchers is how to generate a large number of pairs in order to achieve some practical information-encoding ability. The probability of generating stable pairs decreases exponentially with the number of pairs.
Researchers worldwide are searching for semiconductors that can house quantum states due to the computational boost that quantum information processing could achieve. Today, experimental single-electron transistors can represent only a digital "1" or "0," depending upon whether the charge is present or absent. However, quantum states encode bits in what is known as a "superposition of states," which means that a single electron or photon can represent both logical values simultaneously.
A quantum parameter such as an electron's spin state can be used as the representation of a qubit. As long as the spin of an electron is undisturbed, the qubit represents both a 1 and a 0 simultaneously. When the spin of one electron interacts with another, the result can perform parallel computations on all the values encoded into their wavefunction.
Unfortunately, the very thing that makes quantum systems useful-their ability to superpose values-makes them even more prone to errors than classical systems. The nebulous state of qubits can be destroyed by a wide variety of factors, all of which boil down to an inadvertent coupling to the environment, resulting in decoherence of the superposed values.
To solve this problem, quantum error-correction methods were proposed as early as 1995 and first demonstrated in 1998. Since then, many groups have refined quantum error-correction encoding techniques, which basically replicate a nebulous qubit's value onto separate physical systems that are "entangled"-that is, their nebulous values are synchronized over time despite different physical locations.
Entanglement enables observers to subsequently "compare" the resultant qubits after a calculation, without "observing" their nebulous values, to see if any differences arose between the copies. Such differences indicate an error, which usually resets the system to try that calculation over again. Entanglement also aids in cryptography by being able to detect eavesdropping.
In the University of Michigan work, Merlin's group achieved entanglement of three noninteracting electrons, by virtue of a 5-watt, 532-nanometer laser producing 130-femtosecond pulses at 82 MHz, focused down to a dot with a diameter of 400 microns. Each laser pulse supplied the energy to create what physicists call an exciton-a bound electron-hole pair-with a diameter of about 5 nm in a cadmium-tellurium quantum well. Electrons within that radius from donor manganese impurities in the quantum well became entangled. In the experiment, three such noninteracting electrons were entangled.
"The source of our qubits is electrons bound to donors-here, manganese impurities in a cadmium-tellurium quantum well," said Merlin. "In principle we could entangle thousands of electrons, making our method very scalable."
The formation of excitons from an electron-hole pair is a coulomb interaction, here resulting from the optical energy added by the laser to confined paramagnetic manganese impurities in the presence of a magnetic field. The distance between the electron and hole within the exciton is called the Bohr radius-in this case, it's 5 nm.
Excitons typically move freely within a bulk semiconductor, but when the exciton is trapped in a well, thin wire or quantum dot with dimensions of the same order as the exciton, a confinement effect occurs. A quantum well confines the exciton in only one dimension, leaving it free in the other two, while a quantum wire confines it in two dimensions, leaving it only one dimension in which to move. A quantum dot confines the exciton in all three dimensions.
"We have shown that electrons can be optically excited to generate many-spin Raman coherences in nonoverlapping ex-citons," Merlin said. "Our procedure is potentially set-specific and scalable for quantumcomputing applications."
In the experiment, the manganese electrons within the radius of the exciton became entangled after three laser bursts. With repeated laser bursts, Merlin proposes to entangle an arbitrary number of electrons using his semiconductor-based method. The entanglement was attributed to resonant transitions between Zeeman split spin states-which can be sensed by detecting a harmonic of the fundamental Zeeman frequency that corresponds to the number of entangled electrons. In the experiment, three electrons were entangled, shown by detecting the third harmonic of the Zeeman frequency.
"Our method, relying on the exchange interaction between localized excitons and paramagnetic impurities, can in principle be applied to entangle an arbitrarily large number of spins," said Merlin.
Next Merlin intends to use a masking method to make it possible to aim the laser beam at specific regions of the semiconductor, so that the semiconductor device can be addressed randomly. "Reading and writing we have demonstrated here, but only for an ensemble of electrons. Right now it's 'almost' like having a quantum computer, except that we are turning on and off all the bits at the same time. Next we want to use masking to selectively address individual qubits," said Merlin.
Also on Merlin's drawing board is a more refined laser pulse that in addition to forming arbitrary excitons also assists in performing specific quantum calculations. "We want to use pulse shaping to put a little bump here or a spike there," he said. "We think that by shaping the pulse we can control the entire wavefunction of the electron, which you will need to do to perform quantum computations."
Merlin's research was funded by ACS Petroleum Research Fund, the National Science Foundation and the Air Force Office of Scientific Research. The lab is part of Michigan's Frontiers in Optical Coherent and Ultrafast Science Center.
- Chappell Brown contributed to this report


*** For immediate use April 19, 2012Long predicted but never observed, coherent quantum phase slip can be harnessed to develop a novel class of quantum devicesA new type of quantum bit called a "phase-slip qubit", devised by researchers at the RIKEN Advanced Science Institute and their collaborators, has enabled the world's first-ever experimental demonstration of coherent quantum phase slip (CQPS). The groundbreaking result sheds light on an elusive phenomenon whose existence, a natural outcome of the hundred-year-old theory of superconductivity, has long been speculated, but never actually observed.
Superconductivity describes a phenomenon in which electrons pass through certain types of materials without any resistance when cooled below a given temperature. Among the most important applications of superconductivity is the Josephson junction, named after physicist Brian Josephson, who in 1962 predicted that a superconducting current could tunnel between superconductors separated by a thin insulating layer. This phenomenon, the Josephson effect, has been applied in a variety of areas including magnetometer design, voltage standardization, and quantum computing.
Researchers have long known of an intriguing theoretical parallel to the Josephson effect in which insulator and superconductor are reversed: rather than electric charges jumping from one superconducting layer to another across an insulating layer, magnetic flux quanta jump from one insulator to another across a superconducting layer (Figure 1). Quantum tunneling of electrons in the Josephson junction is replaced in this parallel by the coherent "slip" of the phase, a quantum variable that, in superconducting circuits, plays a dual role to that of electric charge.Coherent quantum phase slip (CQPS), as this phenomenon is known, has long been limited to theory-but no more. In a paper in Nature, Oleg Astafiev and colleagues at the RIKEN Advanced Science Institute (ASI) and NEC Smart Energy Research Laboratories report on the first direct observation of CQPS in a narrow superconducting wire of indium-oxide (InOx). The wire is inserted into a larger superconducting loop to form a new device called a phase-slip qubit, with the superconducting layer (the thin wire) sandwiched between insulating layers of empty space (Figure 2).By tuning the magnetic flux penetrating this loop while scanning microwave frequencies, the researchers detected a band gap in the energy curves for the two flux states of the system (Figure 3), just as theory predicts. This gap is a result of quantum mechanics, which prevents the two states from occupying the same energy level, forcing them to tunnel across the superconducting layer-and through a quantum phase-slip in the narrow wire-to avoid it. While demonstrating conclusively the existence of CQPS, the successful experiment also ushers in a novel class of devices that exploit the unique functionality of quantum phase-slip to forge a new path in superconducting electronics.For more information, please contact:Tsai Jaw-ShenMacroscopic Quantum Coherence TeamRIKEN Advanced Science InstituteTel: +81-(0)29-850-1161 / Fax: +81-(0)29-850-2624Global Relations OfficeRIKENTel: +81-(0)48-462-1225 / Fax: +81-(0)48-463-3687Email: firstname.lastname@example.orgReach us on Twitter: @rikenresearchReferenceO. V. Astafiev, L. B. Ioffe, S. Kafanov, Yu. A. Pashkin, K. Yu. Arutyunov, D. Shahar, O. Cohen, & J. S. Tsai. "Coherent quantum phase slip." Nature, 2012, DOI: 10.1038/nature10930
About RIKENRIKEN is Japan's flagship research institute devoted to basic and applied research. Over 2500 papers by RIKEN researchers are published every year in reputable scientific and technical journals, covering topics ranging across a broad spectrum of disciplines including physics, chemistry, biology, medical science and engineering. RIKEN's advanced research environment and strong emphasis on interdisciplinary collaboration has earned itself an unparalleled reputation for scientific excellence in Japan and around the world.About the Advanced Science Institute.The RIKEN Advanced Science Institute (ASI) is an interdisciplinary research institute devoted to fostering creative, curiosity-driven basic research and sowing the seeds for innovative new projects. With more than 700 full-time researchers, the ASI acts as RIKEN's research core, supporting inter-institutional and international collaboration and integrating diverse scientific fields including physics, chemistry, engineering, biology and medical science.About NECNEC Corporation is a leader in the integration of IT and network technologies that benefit businesses and people around the world. By providing a combination of products and solutions that cross utilize the company's experience and global resources, NEC's advanced technologies meet the complex and ever-changing needs of its customers. NEC brings more than 100 years of expertise in technological innovation to empower people, businesses and society. For more information, visit NEC athttp://www.nec.com.


In contrast to classical bits of information that are either or , quantum bits—or “qubits”—can be in superposition states of and . Just like classical bits, however, qubits are physical objects that have to be implemented in real physical systems. Researchers have used single photons as physical qubits, with the quantum information encoded in terms of polarization, angular momentum, and many other degrees of freedom. The time-bin degree of freedom (that is, encoding quantum information in terms of relative arrival times of light pulses) offers a particularly robust kind of single-photon qubits, and two recent papers have advanced the use of time-bin qubits in dramatic ways.
Writing in Physical Review Letters, Peter Humphreys and colleagues at the University of Oxford, UK, have developed a technique for optical quantum computing using time-bin qubits . In principle, their concept allows photonic quantum computing using a single optical path (or fiber) rather than a maze of multiple paths, thereby drastically reducing the overall complexity of these kinds of systems. Also in Physical Review Letters, John Donohue and colleagues at the Institute for Quantum Computing, University of Waterloo, Canada, have demonstrated an ultrafast measurement technique for time-bin qubits that could enable higher data rates and fewer errors in photonic systems . These two developments represent a huge step towards the realization of practical quantum information processing devices using single-photon qubits.
Time-bin qubits were originally developed by a group at the University of Geneva, Switzerland . To understand the basic form of these qubits, consider a single-photon wave packet passing through a two-path Mach-Zehnder interferometer: if the two paths have different lengths, the photon wave packet will exit the interferometer in a quantum-mechanical superposition of an “early time bin” and “later time bin.” By adjusting the parameters of the interferometer to control relative phase and amplitude, one can accurately produce arbitrary time-bin qubits. The Geneva group famously showed that these time-bin qubits could propagate over long distances in optical fibers with very little decoherence, allowing much more robust quantum communication systems than those based on polarization-encoded qubits [4, 5].
Extending these ideas from the realm of quantum communication, Humphreys et al. have now shown that it is possible to use time-bin qubits for quantum computing . Their approach is based on the well-known linear optics quantum computing (LOQC) paradigm that uses large numbers of ancilla photons and measurement-based nonlinearities to realize near-deterministic quantum logic gates . Previous work on the LOQC approach has primarily been based on polarization qubits and spatial modes that can quickly escalate into extremely unwieldy nested interferometers with very large numbers of paths that need to be stabilized to subwavelength precision [6, 7, 8]. In contrast, Humphreys et al. have now shown that the use of time-bin qubits enables the LOQC approach in a single spatial mode, offering the possibility of far less experimental complexity and a potential for reduced decoherence mechanisms.
As shown in Fig. 1, their approach involves a large string of time-bin qubits propagating along a single waveguide (such as an optical fiber), with the available polarization degree of freedom used to define a “register” mode for propagation and storage, and a “processing” mode for qubit manipulations. As the qubits propagate along the waveguide, Humphreys et al. pull out various time bins from the register mode, process them with phase shifts, bit flips, and couplings, and then return them to the register mode in a coherent way. The authors used these ideas to propose the full suite of single-qubit operations and two-qubit entangling gates needed for universal quantum computation. The validity of their basic method was demonstrated in a very convincing experiment that used single-photon qubits and linear optical elements for time-bin creation and manipulation .
In any approach to quantum information processing, one of the key requirements is the ability to measure arbitrary qubit states. For the time-bin qubits discussed here, this turns out to mean that the separation between the “early” and “late” time bins has to be much greater than the resolution time of the photon detection system being used. With commercially available devices, this typically requires nanosecond-scale separation of the time bins and limits the effective “data rate” for sending time-bin qubits down a quantum channel. Using a radical departure from traditional time-bin qubit detection techniques, Donohue et al. have now pushed this number down to the picosecond scale, offering the potential for much higher information density .
The approach of Donohue et al. is essentially a clever method for coherently converting time bins into “frequency bins” that can be easily measured with slow detectors—even when the time bins are pushed arbitrarily close together. As illustrated in the inset to Fig. 1, this time-to-frequency conversion is based on qubit frequency conversion techniques that mix a single-photon qubit with an auxiliary strong laser pulse in a nonlinear medium . By oppositely “chirping” the qubit and strong laser signals (i.e., stretching them so that their frequencies vary oppositely in time—like mirror-image rainbows), the authors were able to show that the time-bin information maps perfectly into corresponding frequency bins. The real power of the technique—the ability to make measurements of arbitrary time-bin qubits—arises when the auxiliary laser pulse is also put into a superposition of time bins. Using this approach, Donohue et al. were able to experimentally demonstrate ultrafast measurements on arbitrary time-bin states .
The next steps for moving these two new promising ideas from the research lab towards “practical quantum information processing devices” will be of a more technical nature. For Humphrey’s time-bin LOQC approach, this simply means an emphasis on improving the efficiency of the photonics technologies (switches, phase shifters, etc.) needed, while for Donohue’s ultrafast time-bin qubit detectors, it means improving the efficiency of the time-to-frequency conversion process. Combining these ideas with other recent advances in photonic quantum information processing is also an exciting prospect. For example, chip-based devices have recently demonstrated remarkable stability , and a hybrid scheme involving several spatial modes with Humphrey’s temporal methods  and Donohue’s ultrafast detection scheme  may enable near-term realizations of quantum circuits with more than “a few” single-photon qubits.
- P. C. Humphreys, B. J. Metcalf, J. B. Spring, M. Moore, X-M. Jin, M. Barbieri, W. S. Kolthammer, and I. A. Walmsley, “Linear Optical Quantum Computing in a Single Spatial Mode,” Phys. Rev. Lett. 111, 150501 (2013).
- J. M. Donohue, M. Agnew, J. Lavoie, and K. J. Resch, “Coherent Ultrafast Measurement of Time-Bin Encoded Photons,” Phys. Rev. Lett. 111, 153602 (2013).
- J. Brendel, N. Gisin, W. Tittel, and H. Zbinden, “Pulsed Energy-Time Entangled Twin-Photon Source for Quantum Communication,” Phys. Rev. Lett. 82, 2594 (1999).
- I. Marcikic, H. de Riedmatten, W. Tittel, H. Zbinden, M. Legré, and N. Gisin, “Distribution of Time-Bin Entangled Qubits over 50 km of Optical Fiber,” Phys. Rev. Lett. 93, 180502 (2004).
- J. D. Franson, “Bell Inequality for Position and Time,” Phys. Rev. Lett. 62, 2205 (1989).
- E. Knill, R. LaFlamme, and G. J. Milburn, “A Scheme for Efficient Quantum Computation with Linear Optics,” Nature (London) 409, 46 (2001).
- T. B. Pittman, M. J. Fitch, B. C. Jacobs, and J. D. Franson, “Experimental Controlled-NOT Logic Gate for Single Photons in the Coincidence Basis,” Phys. Rev. A 68,032316 (2003).
- J. L. O’Brien, G. J. Pryde, A. G. White, T. C. Ralph, and D. Branning, “Demonstration of an All-Optical Quantum Controlled-NOT Gate,” Nature (London) 426, 264 (2003).
- J. Huang and P. Kumar, “Observation of Quantum Frequency Conversion,” Phys. Rev. Lett. 68, 2153 (1992).
- A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, “Silica-on-Silicon Waveguide Quantum Circuits,” Science 320, 646 (2008).


Tiny 'spherules' reveal details about Earth's asteroid impacts
Researchers are learning details about asteroid impacts going back to Earth's early history by using a new method for extracting precise information from tiny "spherules" embedded in layers of rock. The spherules were created when asteroids crashed into Earth, vaporizing rock that expanded into space as a giant vapor plume. Small droplets of molten and vaporized rock in the plume condensed and solidified, falling back to Earth as a thin layer. The round or oblong particles were preserved in layers of rock, and now researchers have analyzed them to record precise information about asteroids impacting Earth from 3.5 billion to 35 million years ago.
"What we have done is provide the foundation for understanding how to interpret the layers in terms of the size and velocity of the asteroid that made them," said Jay Melosh, an expert in impact cratering and a distinguished professor of earth and atmospheric sciences, physics and aerospace engineering at Purdue University.
Findings, which support a theory that Earth endured an especially heavy period of asteroid bombardment early in its history, are detailed in a research paper appearing online in the journal Nature on April 25. The paper was written by Purdue physics graduate student Brandon Johnson and Melosh. The findings, based on geologic observations, support a theoretical study in a companion paper in Nature by researchers at the Southwest Research Institute in Boulder, Colo.
The period of heavy asteroid bombardment -- from 4.2 to 3.5 billion years ago -- is thought to have been influenced by changes in the early solar system that altered the trajectory of objects in an asteroid belt located between Mars and Jupiter, sending them on a collision course with Earth.
"That's the postulate, and this is the first real solid evidence that it actually happened," Melosh said. "Some of the asteroids that we infer were about 40 kilometers in diameter, much larger than the one that killed off the dinosaurs about 65 million years ago that was about 12-15 kilometers. But when we looked at the number of impactors as a function of size, we got a curve that showed a lot more small objects than large ones, a pattern that matches exactly the distribution of sizes in the asteroid belt. For the first time we have a direct connection between the crater size distribution on the ancient Earth and the sizes of asteroids out in space."
Because craters are difficult to study directly, impact history must be inferred either by observations of asteroids that periodically pass near Earth or by studying craters on the moon. Now, the new technique using spherules offers a far more accurate alternative to chronicle asteroid impacts on Earth, Melosh said.
"We can look at these spherules, see how thick the layer is, how big the spherules are, and we can infer the size and velocity of the asteroid," Melosh said. "We can go back to the earliest era in the history of Earth and infer the population of asteroids impacting the planet."
For asteroids larger than about 10 kilometers in diameter, the spherules are deposited in a global layer.
"Some of these impacts were several times larger than the Chicxulub impact that killed off the dinosaurs 65 million years ago," Johnson said. "The impacts may have played a large role in the evolutional history of life. The large number of impacts may have helped simple life by introducing organics and other important materials at a time when life on Earth was just taking hold."
A 40-kilometer asteroid would have wiped out everything on Earth's surface, whereas the one that struck 65 million years ago killed only land animals weighing more than around 20 kilograms.
"Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes," Johnson said. "However, the spherule layers, if preserved in the geologic record, provide information about an impact even when the source crater cannot be found."
The Purdue researchers studied the spherules using computer models that harness mathematical equations developed originally to calculate the condensation of vapor.
"There have been some new wrinkles in vapor condensation modeling that motivated us to do this work, and we were the first to apply it to asteroid impacts," Melosh said.
The spherules are about a millimeter in diameter.
The researchers also are studying a different type of artifact similar to spherules but found only near the original impact site. Whereas the globally distributed spherules come from the condensing vaporized rock, these "melt droplets" are from rock that's been melted and not completely vaporized.
"Before this work, it was not possible to distinguish between these two types of formations," Melosh said. "Nobody had established criteria for discriminating between them, and we've done that now."
One of the authors of the Southwest Research Institute paper, David Minton, is now an assistant professor of earth and atmospheric sciences at Purdue.
Findings from the research may enable Melosh's team to enhance an asteroid impact effects calculator he developed to estimate what would happen if asteroids of various sizes were to hit Earth. The calculator, "Impact: Earth!" allows anyone to calculate potential comet or asteroid damage based on the object's mass.
The research has been funded by NASA.
Source: Purdue University
- 'Spherules' tell of asteroid impactsfrom UPIWed, 25 Apr 2012, 22:00:21 EDT
- Tiny 'spherules' reveal details about Earth's asteroid impactsfrom Science DailyWed, 25 Apr 2012, 16:31:03 EDT
- Asteroid orbs offer more precise data than cratersfrom CBC: Technology & ScienceWed, 25 Apr 2012, 14:00:20 EDT
- Tiny 'spherules' reveal details about Earth's asteroid impactsfrom PhysorgWed, 25 Apr 2012, 13:00:39 EDT
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