New method to detect quantum mechanical effects in ordinary objects

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Scanning electron micrograph of a superconducting qubit in close proximity to a nanomechanical resonator. The nanoresonator is the bilayer (silicon nitride/aluminum) beam spanning the length of the trench in the center of the image; the qubit is the aluminum island located to the left of the nanoresonator. An aluminum electrode, located adjacent to the nanoresonator on the right, is used to actuate and sense the nanoresonator's motion. Credit: Electron beam lithography was performed by Richard Muller at JPL. Nanoresonator etch was performed by Junho Suh in the Roukes Lab. Image taken by Junho Suh.
At the quantum level, the atoms that make up matter and the photons that make up light behave in a number of seemingly bizarre ways. Particles can exist in "superposition," in more than one state at the same time (as long as we don't look), a situation that permitted Schrödinger's famed cat to be simultaneously alive and dead; matter can be "entangled" -- Albert Einstein called it "spooky action at a distance" -- such that one thing influences another thing, regardless of how far apart the two are.

Previously, scientists have successfully measured entanglement and superposition in photons and in small collections of just a few atoms. But physicists have long wondered if larger collections of atoms--those that form objects with sizes closer to what we are familiar with in our day-to-day life--also exhibit quantum effects.
"Atoms and photons are intrinsically quantum mechanical, so it's no surprise if they behave in quantum mechanical ways. The question is, do these larger collections of atoms do this as well," says Matt LaHaye, a postdoctoral research scientist working in the laboratory of Michael L. Roukes, a professor of physics, applied physics, and bioengineering at the California Institute of Technology (Caltech) and codirector of Caltech's Kavli Nanoscience Institute.
"It'd be weird to think of ordinary matter behaving in a quantum way, but there's no reason it shouldn't," says Keith Schwab, an associate professor of applied physics at Caltech, and a collaborator of Roukes and LaHaye. "If single particles are quantum mechanical, then collections of particles should also be quantum mechanical. And if that's not the case--if the quantum mechanical behavior breaks down--that means there's some kind of new physics going on that we don't understand."
The tricky part, however is devising an experiment that can detect quantum mechanical behavior in such ordinary objects—without, for example, those effects being interfered with or even destroyed by the experiment itself.
Now, however, LaHaye, Schwab, Roukes, and their colleagues have developed a new tool that meets such fastidious demands and that can be used to search for quantum effects in a ordinary object. The researchers describe their work in the latest issue of the journal Nature.
In their experiment, the Caltech scientists used microfabrication techniques to create a very tiny nanoelectromechanical system (NEMS) resonator, a silicon-nitride beam—just 2 micrometers long, 0.2 micrometers wide, and weighing 40 billionths of a milligram—that can resonate, or flex back and forth, at a high frequency when a voltage is applied.
A small distance (300 nanometers, or 300 billionths of a meter) from the resonator, the scientists fabricated a second nanoscale device known as a single-Cooper-pair box, or superconducting "qubit"; a qubit is the basic unit of quantum information.
The superconducting qubit is essentially an island formed between two insulating barriers across which a set of paired electrons can travel. In the Caltech experiments, the qubit has only two quantized energy states: the ground state and an excited state. This energy state can be controlled by applying microwave radiation, which creates an electric field.
Because the NEMS resonator and the qubit are fabricated so closely together, their behavior is tightly linked; this allows the NEMS resonator to be used as a probe for the energy quantization of the qubit. "When the qubit is excited, the NEMS bridge vibrates at a higher frequency than it does when the qubit is in the ground state," LaHaye says.
One of the most exciting aspects of this work is that this same coupling should also enable measurements to observe the discrete energy levels of the vibrating resonator that are predicted by quantum mechanics, the scientists say. This will require that the present experiment be turned around (so to speak), with the qubit used to probe the NEMS resonator. This could also make possible demonstrations of nanomechanical quantum superpositions and Einstein's spooky entanglement
"Quantum jumps are, perhaps, the archetypal signature of behavior governed by quantum effects," says Roukes. "To see these requires us to engineer a special kind of interaction between our measurement apparatus and the object being measured. Matt's results establish a practical and really intriguing way to make this happen."
More information: The paper, "Nanomechanical measurements of a superconducting qubit," was published in the June 18 issue of Nature.
Source: California Institute of Technology (news : web)

Most Efficient And Stable Source Of Pure White Light Ever Achieved

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ScienceDaily (June 19, 2009) — Researchers are reporting the first use of a fundamentally new approach in the quest to snare the Holy Grail of the lighting industry: An LED (light-emitting diode) — those ultra-efficient, long-lived light sources — that emits pure white light. The new approach yielded what the scientists describe as the most efficient and stable source of pure white light ever achieved. The advance could speed the development of this next-generation technology for improved lighting of homes, offices, displays, and other applications, they say.

Soo Young Park and colleagues note that white LEDs show promise as a brighter, longer-lasting and more energy-efficient light source than conventional lighting, such as incandescent and fluorescent lights, which they may replace in the future. But scientists have had difficulty producing white LEDs that are suitable for practical use. Existing technologies produce tinted shades of white light, require complex components, and become unstable over time.
The researchers describe development of a new, simpler white LED that is the first to achieve stable white light emissions using a single molecule. Their specially engineered molecule combines two light-emitting materials, one orange and one blue, which together produce white light over the entire visible range. In laboratory studies, the scientists showed that light production from an LED using the new molecule was highly efficient and had excellent color stability and reproducibility, features that make it a practical white light source.
Journal reference:
Park et al. A White-Light-Emitting Molecule: Frustrated Energy Transfer between Constituent Emitting Centers. Journal of the American Chemical Society, 2009; 090610145759060 DOI: 10.1021/ja902533f
Adapted from materials provided by American Chemical Society.

ATLAS (LHC,CERN) e-News: Category 1, on shift

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To get any physics out of ATLAS, we must manage the data that will course through its cables, from the shifts in the control room to data distribution and software. Christophe Clement, Run Coordinator of ATLAS, describes this important work as less visible since it doesn’t directly result in papers. “And there’s a lot of it,” he adds. “Nevertheless, this is the work that really makes you feel you are carrying out an experiment which has to do with reality.”Control room tasks make up only about 13 per cent of the operation activities, according to Steinar Stapnes, who deals with Operation Task overall planning in ATLAS almost daily, yet they are essential. “Any failure in coverage can have bad consequences, perhaps for hardware and certainly for data taking,” he says.Each institute needs to take its turn on shift; this critical work cannot be compensated for with other contributions that are easier to accomplish remotely or require less diligent attention. For this reason, the Operation Task Planning group has split the operation tasks into two categories: 1 and 2.Category 1 tasks are the real-time operation and monitoring of detector performance, and first line of defence when problems arise, carried out by shifters in the control room and the experts who are called in at anytime of the day or night, should something go wrong. “We make sure that these very important tasks are well-covered. Everybody should feel responsible for them,” says Steinar.He also emphasizes the tradition in particle physics of making sure that graduate students and post-docs get time in the driver’s seat. “For most young people, it’s incredibly interesting, educational, and rewarding for them to get the experience of being part of the team that operates the detector,” says Steinar.Anything beyond the shifts will be Category 2. This includes data acquisition and core software development and maintenance, databases, calibrations, managing data distribution through the Grid, recalibration of data as the detectors are better understood, and software tuning. Category 2 also comprises other tasks associated with processing the data for analysis and those related to longer-term hardware and software maintenance at Point 1.Along with the special designation for shifts and on-call time, the scheduling system has changed. Run Coordination wants to foster a team spirit among the shifters, bringing groups together multiple times over the course of a week. Christophe explained that in this team-based system, shifters: “Get to know the other crew members better, make new contacts, and become more confident with the operation of their sub-detector. Basically work more as a crew.” “It’s not something new in some sense; other experiments have done similar things,” says Steinar, “but it is different with ATLAS because of a larger crew and a large collaboration.”Since collaborators may only work shifts for a maximum of six consecutive days, Run Coordination tried to make a schedule with eight-day blocks, each shifter taking one day off during the block. However, this was in the end deemed too rigid, both for people travelling to CERN to do shifts and for CERN residents. This resulted in a spontaneously generated version with three- and four-day blocks. An unintended consequence was that visiting physicists were inclined to take two blocks in succession, resulting in seven consecutive shifts. CERN safety regulations must be respected, so Run Coordination adjusted the system to allow shifters to choose two consecutive three-day shifts.

This system is also designed to respect the experts who are on-call. In the pattern above, those who work over the weekend have at least a Friday’s worth of experience. This way, the teams are more likely to be able to handle problems without calling in an expert. Christophe notes that on the first day, shifters tend to do some re-learning, but during the rest of a block: “you’ve done this yesterday, and you know what is the problem and how to fix it.”Also, those who take night shift must have recent experience on a day or evening shift, to avoid exhausting the on-call experts with midnight questions and visits to the Control Room. Between the category definitions and block scheduling for shifts, the running of the ATLAS detector should be smooth and effective, with each institution carrying its weight on the front lines.The system starts up Week 26 (28 June to 4 July). For more information or to book a shift, check the webpage.

Katie McAlpine
ATLAS e-News

ATLAS (LHC,CERN) e-News: Cosmic shakedown

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For the last seven weeks, ATLAS has been going through the motions, practicing and problem-solving in preparation for beam.Like a choir rehearsing ahead of a concert, the first five weeks – so called ‘slice weeks’ – each focused on running different combinations of parts of the detector, to inspect how each performed and cooperated.Week 1, commencing April 13th, was all about the SCT, Pixels, and Beam Condition Monitor.

Week 2 dealt with the Tile and Liquid Argon calorimeters, the L1 Calo trigger system, and some High Level Trigger (HLT) algorithms specific to the calorimeters. The third week concentrated on the suite of muon sub-systems.Week 4 took things up a notch, combining all of the above and focusing on testing HLT algorithms as much as possible with cosmics. Finally, week 5 was the first time that the forward detectors – LUCID and the Zero Degree Calorimeter – had been run together and integrated into the ATLAS data stream. Look out for articles reporting in more detail on these final two weeks in the next issue of e-News (June 15th).Due to ongoing work on the cooling for the silicon detectors, the SCT and Pixel detectors could not be switched on, and so week 1 involved only the off-detector part of Pixel and SCT electronics, with Monte Carlo data being 'plugged' into their readout devices. The rest of the slice weeks were full cosmic runs.The muon detectors with the largest surface areas can detect 1000 cosmic particles per second, but in LHC conditions, up to 100,000 ‘interesting’ events will be sent to the HLT per second. To simulate the stress on the HLT, ‘fake’ so-called random triggers were layered on top of the cosmic ones.“We’ve tested so far up to 80 kilohertz. The bulk of this is fake triggers, with about 1 kilohertz of real cosmic muons,” says Run Coordinator Christophe Clement. “The HLT can filter out the fake triggers, run algorithms on the real cosmic ones, and then write maybe 200 interesting ones per second to Tier 0.”According to Christophe, the slice weeks have been pretty successful, particularly considering how much the landscape has changed since the detectors were last run together, in Autumn 2008; the Detector Control System (DCS) which monitors the hardware has been upgraded, bits of the detectors have been replaced and repaired, the online software and HLT software have both been upgraded, and the whole detector has been opened and is now almost closed.“I think we can say now that we have upgraded all software for Data Acquisition and Trigger as well as the Detector Control System, and we’re more or less at the same level that we were last year in terms of stability,” says Christophe “and then we start to push more at the trigger rates.”Stability tests, where the system is left to run unhampered for extended periods, were performed on the weekends of the slice weeks. “It’s like a test-program for a plane,” explains Christophe, “they’re going to do all possible things: fly it into a storm, try to land it when it’s snowing. That’s what we do during the week. Then on the Friday evening, we say ‘OK, now we’ll just try to fly straight for the weekend, without touching anything, and see if it works for a long flight’.”Most of the sub-systems were able to run well for extended periods, although there were some unexpected instabilities at high rate. This week and next, experts from the calorimeters and L1 Calo will meet in Geneva to try to get to the bottom of those problems.Weekend tests were also run using a simulated beam schedule, to give groups a better sense of how they will need to work during beam time – stopping and starting and reconfiguring between LHC fills. “We were quite positively surprised at how well we were able to do this,” says Christophe, reporting crude data-taking efficiency calculations of 91 per cent during the long muon weekend. Ignoring a glitch on the general power grid on a certain Sunday morning at 3 a.m., the figure for the calorimeter weekend would have been 97 per cent.Since the slice weeks, more tests have been done with the muon system and the TRT, as ATLAS works towards a two-week combined magnet run, due to begin on June 22nd.“For these two weeks, we hope to run cosmics with less debugging,” says Christophe. “The weeks we had so far were really to try to address technical issues. Hopefully [the combined run] will be much smoother, and we can calculate our data taking efficiency much better.”The data taken so far will be analysed for weeks to come, and used to perfect the calibration, alignment, and synchronisation of ATLAS. Over 40 million cosmic events were triggered in the muon slice week alone, and there is now a big push to bring trigger timings for different parts of the detector and different types of triggers into alignment. When real collision particles start shooting through the different layers of the detector, all the electronics must be synchronised and shouting their findings in unison, a choir hitting its notes in time. “We’re fine-tuning this now,” says Christophe. “If we can get everything within 25 to 50 nanoseconds on the cosmics before the beam it would be a great success. And then we can improve with the collisions.”

Ceri Perkins
ATLAS e-News

Manipulating light on a chip for quantum technologies

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An artist's impression of the on-chip quantum metrology experiment (making ultraprecise measurements on chip) Photo by Will Amery, University of Bristol.

(PhysOrg.com) -- A team of physicists and engineers at Bristol University has demonstrated exquisite control of single particles of light — photons — on a silicon chip to make a major advance towards long-sought-after quantum technologies, including super-powerful quantum computers and ultra-precise measurements.

The Bristol Centre for Quantum Photonics has demonstrated precise control of four photons using a microscopic metal electrode lithographically patterned onto a silicon chip.
The photons propagate in silica waveguides — much like in optical fibres — patterned on a silicon chip, and are manipulated with the electrode, resulting in a high-performance miniaturized device.
“We have been able to generate and manipulate entangled states of photons on a silicon chip” said PhD student, Jonathan Matthews, who together with Alberto Politi performed the experiments. “These entangled states are responsible for famously ‘weird’ behaviour arising in quantum mechanics, but are also at the heart of powerful quantum technologies.”
“This precise manipulation is a very exciting development for fundamental science as well as for future quantum technologies.” said Prof Jeremy O’Brien, Director of the Centre for Quantum Photonics, who led the research.
The team reports its results in the latest issue of Nature Photonics [June 2009], a sister journal of the leading science journal Nature, and in a Postdeadline Paper at 'The International Quantum Electronics Conference (IQEC)' on June 4 in Baltimore, USA [IQEC Postdeadline Papers].
Quantum technologies with photons
Quantum technologies aim to exploit the unique properties of quantum mechanics, the physics theory that explains how the world works at microscopic scales.
For example a quantum computer relies on the fact that quantum particles, such as photons, can exist in a “superposition” of two states at the same time — in stark contrast to the transistors in a PC which can only be in the state “0” or “1”.
Photons are an excellent choice for quantum technologies because they are relatively noise-free; information can be moved around at the speed of light; and manipulating single photons is easy.
Making two photons “talk” to each other to generate the all-important entangled states is much harder, but Professor O’Brien and his colleagues at the University of Queensland demonstrated this in a quantum logic gate back in 2003 [Nature 426, 264 (2003)].

Last year, the Centre for Quantum Photonics at Bristol showed how such interactions between photons could be realised on a silicon chip, pointing the way to advanced quantum technologies based on photons [Science 320, 646 (2008)].
Photons are also required to “talk” to each other to realise the ultra-precise measurements that harness the laws of quantum mechanics. In 2007 Professor O’Brien and his Japanese collaborators reported such a quantum metrology measurement with four photons [Science 316, 726 (2007)].
Manipulating photons on a silicon chip
“Despite these impressive advances, the ability to manipulate photons on a chip has been missing,” said Mr Politi. “For the last several years the Centre for Quantum Photonics has been working towards building fully functional quantum circuits on a chip to solve these problems,” added Prof O’Brien.
The team coupled photons into and out of the chip, fabricated at CIP Technologies, using optical fibres. Application of a voltage across the metal electrode changed the temperature of the silica waveguide directly beneath it, thereby changing the path that the photons travelled. By measuring the output of the device they confirmed high-performance manipulation of photons in the chip.
The researchers proved that one of the strangest phenomena of the quantum world, namely “quantum entanglement”, was achieved on-chip with up to four photons. Quantum entanglement of two particles means that the state of either of the particles is not defined, but only their collective state, and results in an instantaneous linking of the particles.
This on-chip entanglement has important applications in quantum metrology and the team demonstrated an ultra-precise measurement in this way.
“As well as quantum computing and quantum metrology, on-chip photonic quantum circuits could have important applications in quantum communication, since they can be easily integrated with optical fibres to send photons between remote locations,” said Alberto Politi.
“The really exciting thing about this result is that it will enable the development of reconfigurable and adaptive quantum circuits for photons. This opens up all kinds of possibilities,” said Prof O’Brien.
A commentary on the work that appeared in the same issue [Nature Photonics 3, 317 (2009)] described it as “an important step in the quest for quantum computation” and concluded: “The most exciting thing about this work is its potential for scalability. The small size of the [device] means that far greater complexity is possible than with large-scale optics.”
The other co-author of the Nature Photonics paper is Dr André Stefanov, formerly a Research fellow in the Centre for Quantum Photonics, and now at the Federal Office of Metrology METAS, Switzerland.
Provided by University of Bristol (news : web)

Researchers make breakthrough in the quantum control of light

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This image represents a quantum state with zero, three and six photons simultaneously. The theory is on left and the experiment is on the right. Image: UCSB.
Researchers at UC Santa Barbara have recently demonstrated a breakthrough in the quantum control of photons, the energy quanta of light. This is a significant result in quantum computation, and could eventually have implications in banking, drug design, and other applications.

In a paper to be published in today's issue of the journal Nature, UCSB physics researchers Max Hofheinz, John Martinis, and Andrew Cleland document how they used a superconducting electronic circuit known as a Josephson phase qubit to prepare highly unusual quantum states using microwave-frequency photons. The breakthrough is the result of four years of work in the laboratories of Cleland and Martinis.
The project is funded by the federal agency called the Intelligence Advanced Research Projects Activity, or IARPA. The government is particularly interested in quantum computing because of the way banking and other important communications are currently encrypted. Using large numbers, with hundreds of digits, encryption codes are changed daily and would take years of traditional computing to break. Quantum computing could potentially break those codes quickly, destroying current encryption schemes.
In the experiments, the photons were stored in a microwave cavity, a "light trap" in which the light bounces back and forth as if between two mirrors. In earlier work, these researchers showed they could create and store photons, one at a time, with up to 15 photons stored at one time in the light trap. The research shows that they can create states in which the light trap simultaneously has different numbers of photons stored in it. For example, it can simultaneously have zero, three, and six photons at the same time. Measuring the quantum state by counting how many photons are stored forces the trap to "decide" how many there are; but prior to counting, the light trap exists in a quantum superposition, with all three outcomes possible.
Explaining the paradoxical simultaneity of quantum states, Cleland said that it's like having your cake and eating it -- at the same time.
"These superposition states are a fundamental concept in quantum mechanics, but this is the first time they have been controllably created with light," Cleland said. Martinis added, "This experiment can be thought of as a quantum digital-to-analog converter." As digital-to-analog converters are key components in classical communication devices (for example, producing the sound waveforms in cell phones), this experiment might enable more advanced communication protocols for the transmission of quantum information.
First author Hofheinz designed and performed the measurements. He is a postdoctoral researcher from Germany who has been working at UCSB for the last two years on this project. The devices used to perform the experiment were made by Haohua Wang, a postdoctoral researcher from China, who is second author on the Nature publication.
The scientists said their research is leading to the construction of a quantum computer, which will have applications in information encryption and in solving or simulating problems that are not amenable to solution using standard computers.
Source: University of California - Santa Barbara (news : web)

Computer Memory May Leap With Solution To Chemical Mystery

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http://www.sciencedaily.com/releases/2007/10/071019123619.htm

ScienceDaily (Oct. 22, 2007) — A Florida State University researcher has helped solve a scientific mystery that stumped chemists for nearly seven decades. In so doing, his team's findings may lead to the development of more-powerful computer memories and lasers.

Naresh S. Dalal, the Dirac Professor of Chemistry and Biochemistry at FSU, recently collaborated with three colleagues, Jorge Lasave, Sergio Koval and Ricardo Migoni, all of the Universidad Nacional de Rosario in Argentina, to determine why a certain type of crystal known as ammonium dihydrogen phosphate, or ADP, behaves the way it does.
"ADP was discovered in 1938," Dalal said. "It was observed to have some unusual electrical properties that weren't fully understood -- and for nearly 70 years, scientists have been perplexed by these properties. Using the supercomputer at SCRI (FSU's Supercomputer Computations Research Institute), we were able to perform in-depth computational analyses that explained for the very first time what causes ADP to have these unusual properties."
ADP, like many crystals, exhibits an electrical phenomenon known as ferroelectricity. Ferroelectric materials are analogous to magnets in that they maintain a positively charged and a negatively charged pole below a certain temperature that is characteristic for each compound.
"Ferroelectric materials can stay in a given state of charge for a long time -- they retain their charge after the external electrical source is removed," Dalal said. "This has made ADP and other materials like it very useful for storing and transmitting data.
ADP is commonly used in computer memory devices, fiber optic technology, lasers and other electro-optic applications."
What researchers found perplexing about ADP was that it often displays a very different electrical phase -- one known as antiferroelectricity.
"With antiferroelectricity, one layer of molecules in a crystal has a plus and a minus pole, but in the next layer, the charges are reversed," Dalal said. "You see this reversal of charges, layer by layer, throughout the crystal."
Using the supercomputer at SCRI enabled Dalal and his colleagues to perform numerous highly complex calculations that couldn't be duplicated in a laboratory environment. For example, they were able to theoretically alter the angles of ADP's ammonium ions and then measure the effects on the crystal's electrical charge. That approach ultimately led to their solution to the seven-decade mystery.
"We found that the position of the ammonium ions in the compound, as well as the presence of stresses or defects in the crystal, determine whether it behaves in a ferroelectric or antiferroelectric manner," Dalal said.
The team's research is important for two main reasons, Dalal said: "First, this allows us to further understand how to design new materials with both ferroelectric and antiferroelectric properties. Doing so could open new doors for computer memory technology -- and possibly play a role in the development of quantum computers.
"Second, our research opens up new ways of testing materials," Dalal said. "Using supercomputers, we can quickly perform tests to see how materials would react under a variety of conditions. Many such tests can't even be performed in the lab."
A paper "Origin of Antiferroelectricity in NH4H2PO4 from First Principles,"describing Dalal, Lasave and Migoni's findings was published recently in Physical Review Letters.
Adapted from materials provided by Florida State University.

Fausto Intilla

www.oloscience.com

New Quantum Dot Transistor Counts Individual Photons

Source:

http://www.sciencedaily.com/releases/2007/10/071011180823.htm

Science Daily — A transistor containing quantum dots that can count individual photons (the smallest particles of light) has been designed and demonstrated at the National Institute of Standards and Technology (NIST). The semiconductor device could be integrated easily into electronics and may be able to operate at higher temperatures than other single-photon detectors--practical advantages for applications such as quantum key distribution (QKD) for "unbreakable" encryption using single photons.

The NIST device, described in a new paper,* can accurately count 1, 2 or 3 photons at least 83 percent of the time. It is the first transistor-based detector to count numbers of photons; most other types of single-photon detectors simply "click" in response to any small number of photons. (See table for a comparison of various types of single-photon detectors used at NIST.)
Counting requires a linear, stepwise response and low-noise operation. This capability is essential for advanced forms of precision optical metrology--a focus at NIST--and could be used both to detect photons and to evaluate single-photon sources for QKD. The new device also has the potential to be cooled electronically, at much higher temperatures than typical cryogenic photon detectors.
Dubbed QDOGFET, the new detector contains about 1,000 quantum dots, nanoscale clusters of semiconductors with unusual electronic properties. The NIST dots are custom-made to have the lowest energy of any component in the detector, like the bottom of a drain. A voltage applied to the transistor produces an internal current, or channel. Photons enter the device and their energy is transferred to electrons in a semiconductor "absorbing layer," separating the electrons from the "holes" they formerly occupied.
As each photon is absorbed, a positively charged hole is trapped by the quantum dot drain, while the corresponding electron is swept into the channel. The amount of current flowing in the channel depends on the number of holes trapped by quantum dots. By measuring the channel response, scientists can count the detected photons. NIST measurements show that, on average, each trapped hole boosts the channel current by about one-fifth of a nanoampere. The detector has an internal quantum efficiency (percentage of absorbed photons that result in trapped holes) of 68 ± 18 percent, a record high for this type of photon detector.
The QDOGFET currently detects single photons at wavelengths of about 800 nanometers. By using different semiconductor materials, NIST researchers hope to make detectors that respond to the longer near-infrared wavelengths used in telecommunications. In addition, researchers hope to boost the external quantum efficiency (percentage of photons hitting the detector that are actually detected), now below 10 percent, and operate the device at faster speeds.
The research is supported in part by the Disruptive Technology Office. The authors include one from Los Alamos National Laboratory and one from Heriot-Watt University, Edinburgh, UK.
* E.J. Gansen, M.A. Rowe, M.B. Greene, D. Rosenberg, T.E. Harvey, M.Y. Su, R.H. Hadfield, S.W. Nam and R.P. Mirin. Photon-number-discriminating detection using a quantum dot, optically gated, field-effect transistor. Nature Photonics. 1, 585 - 588 (2007). Published on-line Oct. 1, 2007.
Note: This story has been adapted from material provided by National Institute of Standards and Technology.

Fausto Intilla

www.oloscience.com

Novel Semiconductor Structure Bends Light 'Wrong' Way -- Exciting Application Potential

Source:

http://www.sciencedaily.com/releases/2007/10/071014163634.htm

Science Daily — A Princeton-led research team has created an easy-to-produce material from the stuff of computer chips that has the rare ability to bend light in the opposite direction from all naturally occurring materials. This startling property may contribute to significant advances in many areas, including high-speed communications, medical diagnostics and detection of terrorist threats.

The new substance is in a relatively new class of materials called "metamaterials," which are made out of traditional substances, such as metals or semiconductors, arranged in very small alternating patterns that modify their collective properties. This approach enables metamaterials to manipulate light in ways that cannot be accomplished by normal materials.
Previous metamaterials were two-dimensional arrangements of metals, which limited their usefulness. The Princeton invention is the first three-dimensional metamaterial constructed entirely from semiconductors, the principal ingredient of microchips and optoelectronics.
"To be useful in a variety of devices, metamaterials need to be three-dimensional," said Princeton electrical engineering professor Claire Gmachl, one of the researchers on the study. "Furthermore, this is made from semiconductors, which are extremely functional materials. These are the things from which true applications are made."
The research team, led by Princeton engineering graduate student Anthony Hoffman, will publish its findings online Oct. 14 in the journal Nature Materials. Other Princeton researchers on the team include graduate students Leonid Alekseyev, Scott Howard and Kale Franz; former Council of Science and Technology fellow Dan Wasserman, now at the University of Massachusetts-Lowell; and former electrical engineering professor Evgenii Narimanov, now at Purdue University. The team also includes collaborators from Oregon State University and telecommunications firm Alcatel-Lucent.
Light waves and other forms of electromagnetic radiation bend whenever they pass from one medium to another. This phenomenon, called refraction, is readily observable when a straw placed into a glass of water appears to be bent or broken. Lenses in reading glasses or a camera work because of refraction.
All materials have an index of refraction, which measures the degree and direction that light is bent as it passes through them. While materials found in nature have positive refractive indices, the material recently invented by Princeton researchers has a negative index of refraction.
In the case of the straw in a glass, normal water would make the underwater portion of the straw appear to bend toward the surface. If water were able to refract light negatively, as the newly invented semiconductor does, the segment of straw under the water would appear as if it were bending away from the surface
Far more than a neat optical illusion, negative refraction holds promise for the development of superior lenses. The positive refractive indices of normal materials necessitate the use of curved lenses, which inherently distort some of the light that passes through them, in telescopes and microscopes. Flat lenses made from materials that exhibit negative refraction could compensate for this aberration and enable far more powerful microscopes that can "see" things as small as molecules of DNA.
In addition, the Princeton metamaterial is capable of negative refraction of light in the mid-infrared region, which is used in a wide range of sensing and communications applications. Its unique composition results in less lost light than previous metamaterials, which were made of extremely small arrangements of metal wires and rings. The semiconductors that constitute the new material are grown from crystals using common manufacturing techniques, making it less complex, more reliable and easier to produce.
"Currently, the typical infrared lens is a massive object -- the setups are bulky," Hoffman said. "This new material may enable more compact mid-infrared optics because we now have a new material with an entirely new set of optical parameters in our toolkit."
The research is part of a multi-institutional research center called Mid-Infrared Technologies for Health and the Environment (MIRTHE). Researchers at MIRTHE are developing compact sensors that detect trace amounts of gases in the atmosphere and human breath. These could one day be used in devices that monitor air quality and enhance homeland security, as well as in non-invasive and on-the-spot medical tests for diabetes and lung disease.
The research relies on a new type of laser that emits mid-infrared light. Gmachl, who directs the MIRTHE project, said the new material could be used to make the lasers better and smaller.
Next, the team plans to incorporate the new metamaterial into lasers. Additionally, the researchers will continue to modify the material in attempts to make features ever smaller in an effort to expand the range of light wavelengths they are able to manipulate.
The work was supported by the MIRTHE center and the Princeton Center for Complex Materials (PCCM), both sponsored by the National Science Foundation.
Note: This story has been adapted from material provided by Princeton University, Engineering School.

Fausto Intilla

www.oloscience.com

Light Shed On Light-emitting Nanodevice

Source:

http://www.sciencedaily.com/releases/2007/10/071008130207.htm

Science Daily — An interdisciplinary team of Cornell nanotechnology researchers has unraveled some of the fundamental physics of a material that holds promise for light-emitting, flexible semiconductors.
The discovery, which involved years of perfecting a technique for building a specific type of light-emitting device, is reported in the journal Nature Materials.*
The interdisciplinary team had long studied the molecular semiconductor ruthenium tris-bipyridine. For many reasons, including its ability to allow electrons and holes (spaces where electrons were before they moved) to pass through it easily, the material has the potential to be used for flexible light-emitting devices. Sensing, microscopy and flat-panel displays are among its possible applications.
The researchers set out to understand the fundamental physics of the material -- that is, what happens when it encounters an electric field, both at the interfaces and inside the film. By fabricating a device out of the ruthenium metal complex that was spin-coated onto an insulating substrate with pre-patterned gold electrodes, the scientists were able to use electron force microscopy to measure directly the electric field of the device.
A long-standing question, according to George G. Malliaras, associate professor of materials science and engineering, director of the Cornell NanoScale Science and Technology Facility and one of the co-principal investigators, was whether an electric field, when applied to the material, is concentrated at the interfaces or in the bulk of the film.
The researchers discovered that it was at the interfaces -- two gold metal electrodes sandwiching the ruthenium complex film -- which was a huge step forward in knowing how to build and engineer future devices.
"So when you apply the electric field, ions in the material move about, and that creates the electric fields at the interfaces," Malliaras explained.
Essential to the effort was the ability to pattern the ruthenium complex using photolithography, a technique not normally used with such materials and one that took the researchers more than three years to perfect, using the knowledge of experts in nanofabrication, materials and chemistry.
The patterning worked by laying down a gold electrode and a polymer called parylene. By depositing the ruthenium complex on top of the parylene layer and filling in an etched gap between the gold electrodes, the researchers were then able to peel the parylene material off mechanically, leaving a perfect device.
Ruthenium tris-bipyridine has energy levels well suited for efficient light emission of about 600 nanometers, said Héctor D. Abruña, the E.M. Chamot Professor of Chemistry, and a principal co-investigator. The material, which has interested scientists for many years, is ideal for its stability in multiple states of oxidation, which, in turn, allows it to serve as a good electron and hole transporter. This means that a single-layer device can be made, simplifying the manufacturing process.
"It's not fabulous, but it has a reasonable emission efficiency," Abruña said. "One of the drawbacks is it has certain instabilities, but we have managed to mitigate most of them."
Among the other authors were co-principal investigators Harold G. Craighead, the C.W. Lake Jr. Professor of Engineering, and John A. Marohn, associate professor of chemistry and chemical biology.
*September 30
Note: This story has been adapted from material provided by Cornell University.

Fausto Intilla
www.oloscience.com

Taming Tiny, Unruly Waves For Nano Optics

Source:

http://www.sciencedaily.com/releases/2007/10/071008113705.htm

Science Daily — Nanoscale devices present a unique challenge to any optical technology — there’s just not enough room for light to travel in a straight line.

On the nanoscale, energy may be produced by radiating photons of light between two surfaces very close together (sometimes as close as 10 nanometers), smaller than the wavelength of the light. Light behaves much differently on the nanoscale as its wavelength is interrupted, producing unstable waves called evanescent waves. The direction of these unpredictable waves can’t be calculated, so researchers face the daunting task of designing nanotechnologies to work with the tiny, yet potentially useful waves of light.
Researchers at Georgia Tech have discovered a way to predict the behavior of these unruly waves of light during nanoscale radiation heat transfer, opening the door to the design of a spectrum of new nanodevices (or NEMS) and nanotechnologies, including solar thermal energy technologies.
“This discovery gives us the fundamental information to determine things like how far apart plates should be and what size they should be when designing a technology that uses nanoscale radiation heat transfer,” said Zhuomin Zhang, a lead researcher on the project and a professor in the Woodruff School of Mechanical Engineering. “Understanding the behavior of light at this scale is the key to designing technologies to take advantage of the unique capabilities of this phenomenon.”
The Georgia Tech research team set out to study evanescent waves in nanoscale radiation energy transfer (between two very close surfaces at different temperatures by means of thermal radiation). Because the direction of evanescent waves is seemingly unknowable (an imaginary value) in physics terms, Zhang’s group instead decided to follow the direction of the electromagnetic energy flow (also known as a Poynting vector) to predict behavior rather than the direction of the photons.
“We’re using classic electrodynamics to explain the behavior of the waves, not quantum mechanics,” Zhang said. “We’re predicting the energy propagation — and not the actual movement — of the photons.”
The challenge is that electrodynamics work differently on the nanoscale and the Georgia Tech team would need to pinpoint those differences. Planck’s law, a more than 100-year-old theory about how electromagnetic waves radiate, does not apply on the nanoscale due to fact that the space between surfaces is smaller than a wavelength.
The Georgia Tech team observed that instead of normal straight line radiation, the light was bending as protons tunneled through the vacuum in between the two surfaces just nanometers apart. The team also noticed that the evanescent waves were separating during this thermal process, allowing them to visualize and predict the energy path of the waves.
Understanding the behavior of such waves is critical to the design of many devices that use nanotechnology, including near-field thermophotovoltaic systems, nanoscale imaging based on thermal radiation scanning tunneling microscopy and scanning photon-tunneling microscopy, said Zhang.
These findings were featured on the cover of the Oct. 8 issue of Applied Physics Letters.
Note: This story has been adapted from material provided by Georgia Institute of Technology.

Fausto Intilla

www.oloscience.com

Laser Joining Of Solar Cells

Source:

http://www.sciencedaily.com/releases/2007/10/071007203636.htm

Science Daily — A single solar cell produces a relatively low output – it’s a case of strength in numbers. Tiny strips of metal are used to link cells together. If the laser soldering temperature is too high, the solder joint may fracture. A new system provides automatic temperature regulation.

Teamwork is what matters – even in the case of solar cells: To obtain sufficient power to operate a pocket calculator, parking ticket dispenser or photovoltaic module, sunlight has to be captured simultaneously by an array of cells. They are connected in series using tiny strips of metal known as stringers. Each stringer has to be positioned in precisely the right spot, then its solder coating is melted using a hot electrode.
When the solder sets, it forms a stable bond with the metallic coating on the silicon. The amount of heat induced in the stringer and the silicon depends on the contact between the soldering electrode and the stringer. Applying too much energy causes thermal stress which in the worst case could destroy the solder joint, leaving a break in the electrical circuit that makes the solar module unfit for use.
Researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have developed a non-contact soldering system in which the temperature is constantly monitored. If the temperature deviates beyond set limits, the system automatically adjusts it to an acceptable value. “Instead of an electrode, we use a laser beam for the soldering operation,” says ILT department head Dr. Arnold Gillner.
“To melt the solder, we pass a laser beam over the solder-coated stringer. An infrared heat camera derives the temperature of the silicon and of the metal strip from real-time measurements of their emitted radiant heat. If the temperature is too high or too low, a feedback control circuit automatically adapts the laser output within milliseconds.” The system is already in use for industrial surface engineering applications. Solar applications could be on the market in a year or so.
The researchers’ next project is to develop a faster, more reliable method of connecting solar cells by means of laser welding. “Whereas soldering only involves melting the solder, in laser welding the stringer itself is melted,” explains Gillner. This means applying more heat than for soldering, but only for a very short time. “Since the laser is only in contact with the materials for a brief instant, only a small amount of energy is transferred to the materials despite the higher temperature – resulting in even fewer heat-induced defects,” he adds.
What complicates the matter is the fact that the stringer has a diameter of about 200 micrometers, whereas the metallic coating on the silicon required to conduct electricity has a thickness of a mere 10 micrometers. The laser beam has to be modulated in such a way that the stringer will melt while leaving the coating on the silicon intact.
Note: This story has been adapted from material provided by Fraunhofer-Gesellschaft.

Fausto Intilla

www.oloscience.com

What Makes Quantum Dots Blink?

Source:

http://www.sciencedaily.com/releases/2007/10/071004165602.htm

Science Daily — In order to learn more about the origins of quantum dot blinking, researchers from the U.S. Department of Energy's Argonne National Laboratory, the University of Chicago and the California Institute of Technology have developed a method to characterize it on faster time scales than have previously been accessed.

Nanocrystals of semiconductor material, also known as quantum dots, are being intensively investigated for applications such as light-emitting diodes, solid-state lighting, lasers, and solar cells. They are also already being applied as fluorescent labels for biological imaging, providing several advantages over the molecular dyes typically used, including a wider range of emitted colors and much greater stability.
Quantum dots have great promise as light-emitting materials, because the wavelength, or color, of light that the quantum dots give off can be very widely tuned simply by changing the size of the nanoparticles. If a single dot is observed under a microscope, it can be seen to randomly switch between bright and dark states.
This flickering, or blinking, behavior has been widely studied, and it has been found that a single dot can blink off for times that can vary between microseconds and several minutes. The causes of the blinking, though, remain the subject of intense study.
The methods developed by Matt Pelton of Argonne's Center for Nanoscale Materials and his team of collaborators has revealed a previously unobserved change in the blinking behavior on time scales less than a few microseconds. This observation is consistent with the predictions of a model for quantum-dot blinking previously developed by Nobel Laureate Rudolph Marcus, contributor to this research, and his co-workers. In this model, the blinking is controlled by the random fluctuation of energy levels in the quantum dot relative to the energies of trap states on the surface of the nanocrystal or in the nearby environment.
The results of this research provide new insight into the mechanism of quantum-dot blinking, and should help in the development of methods to control and suppress blinking. Detailed results of this work have been published in a paper in the Proceedings of the National Academy of Sciences.
Argonne's Center for Nanoscale Materials work for this research was funded by the U.S. Department of Energy's Office of Basic Energy Science.
Note: This story has been adapted from material provided by DOE/Argonne National Laboratory.

Fausto Intilla

www.oloscience.com

Nature Leads The Way For The Next Generation Of Paints, Cosmetics And Holograms

Source:

http://www.sciencedaily.com/releases/2007/10/071003100546.htm

Science Daily — A plant-like micro-organism mostly found in oceans could make the manufacture of products, from iridescent cosmetics, paints and fabrics to credit card holograms, cheaper and 'greener.'

The tiny single-celled 'diatom', which first evolved hundreds of millions of years ago, has a hard silica shell which is iridescent -- in other words, the shell displays vivid colours that change depending on the angle at which it is observed. This effect is caused by a complex network of tiny holes in the shell which interfere with light waves.
UK scientists have now found an extremely effective way of growing diatoms in controlled laboratory conditions, with potential for scale-up to industrial level. This would enable diatom shells to be mass-produced, harvested and mixed into paints, cosmetics and clothing to create stunning colour-changing effects, or embedded into polymers to produce difficult-to-forge holograms.
Manufacturing consumer products with these properties currently requires energy-intensive, high-temperature, high-pressure industrial processes that create tiny artificial reflectors. But farming diatom shells, which essentially harnesses a natural growth process, could provide an alternative that takes place at normal room temperature and pressure, dramatically reducing energy needs and so cutting carbon dioxide emissions. The process is also extremely rapid -- in the right conditions, one diatom can give rise to 100 million descendants in a month.
This ground-breaking advance has been achieved by scientists at the Natural History Museum and the University of Oxford, with funding from the Engineering and Physical Sciences Research Council (EPSRC). The project involved a range of experts from disciplines including biology, chemistry, physics, engineering and materials science.
"It's a very efficient and cost-effective process, with a low carbon footprint," says Professor Andrew Parker, who led the research. "Its simplicity and its economic and environmental benefits could in future encourage industry to develop a much wider range of exciting products that change colour as they or the observer move position. What's more, the shells themselves are completely biodegradable, aiding eventual disposal and further reducing the environmental impact of the process life cycle."
The new technique basically lets nature do the hard work. It involves taking a diatom or other living cells such as those that make iridescent butterfly scales, and immersing them in a culture medium -- a solution containing nutrients, hormones, minerals etc that encourage cell subdivision and growth. By changing the precise make-up of the culture medium, the exact iridescent properties of the diatoms or butterfly scales (and therefore the final optical effects that they create) can be adjusted. The researchers estimate that up to 1 tonne/day of diatoms could be produced in the laboratory in this way, starting from just a few cells. Within as little as two years, an industrial-scale process could be operational.
"It's a mystery why diatoms have iridescent qualities," says Professor Parker. "It may have something to do with maximising sunlight capture to aid photosynthesis in some species; on the other hand, it could be linked with the need to ensure that sunlight capture is not excessive in others. Whatever the case, exploiting their tiny shells' remarkable properties could make a big impact across industry. They could even have the potential to be incorporated into paint to provide a water-repellent surface, making it self-cleaning."
The 12-month research project 'Optics via Cell Culture' received EPSRC funding of just over £104,000. The research took place at the Natural History Museum in London and at the University of Oxford.
About diatoms :
Diatoms are classified as eukaryotic algae and represent one of the commonest types of phytoplankton. Each diatom is encased in a silica frustule, or cell wall. Although usually microscopic, some species of diatom may grow to as much as 2mm long. As well as oceans, diatoms can be found in freshwater and in damp soils. In the oceans, they represent an important link in the food chain.
When light strikes a diatom's shell, tiny holes in the shell's structure cause multiple reflections, resulting in interference to the light waves. This affects the shell's colour, as seen by an observer. The precise interference effect depends on the angle at which light strikes the shell (i.e. the angle of observation), hence the shell appears to change colour as it or the observer moves position. This is the same sort of phenomenon that occurs when light reflects from a film of oil on the surface of water -- viewed from different angles, the oil's colours seem to change. While some light is reflected, however, certain wavelengths are transmitted into the cell. The device acts like a 'photonic crystal.'
Note: This story has been adapted from material provided by Engineering and Physical Sciences Research Council.

Fausto Intilla

www.oloscience.com

Physicist Defends Einstein's Theory And 'Speed Of Gravity' Measurement

Source:

http://www.sciencedaily.com/releases/2007/10/071003130816.htm

Science Daily — Scientists have attempted to disprove Albert Einstein's theory of general relativity for the better part of a century. After testing and confirming Einstein's prediction in 2002 that gravity moves at the speed of light, a professor at the University of Missouri-Columbia has spent the past five years defending the result, as well as his own innovative experimental techniques for measuring the speed of propagation of the tiny ripples of space-time known as gravitational waves.
Sergei Kopeikin, associate professor of physics and astronomy in the College of Arts and Science, believes that his latest article, "Gravimagnetism, causality, and aberration of gravity in the gravitational light-ray deflection experiments" published along with Edward Fomalont from the National Radio Astronomical Observatory, arrives at a consensus in the continuing debate that has divided the scientific community.
An experiment conducted by Fomalont and Kopeikin five years ago found that the gravity force of Jupiter and light travel at the same speed, which validates Einstein's suggestion that gravity and electromagnetic field properties, are governed by the same principle of special relativity with a single fundamental speed. In observing the gravitational deflection of light caused by motion of Jupiter in space, Kopeikin concluded that mass currents cause non-stationary gravimagnetic fields to form in accordance with Einstein's point of view.
Einstein believed that in order to measure any property of gravity, one has to use test particles. "By observing the motion of the particles under influence of the gravity force, one can then extract properties of the gravitational field," Kopeikin said. "Particles without mass -- such as photons -- are particularly useful because they always propagate with constant speed of light irrespectively of the reference frame used for observations."
"The property of gravity tested in the experiment with Jupiter also is called causality. Causality denotes the relationship between one event (cause) and another event (effect), which is the consequence (result) of the first. In the case of the speed of gravity experiment, the cause is the event of the gravitational perturbation of photon by Jupiter, and the effect is the event of detection of this gravitational perturbation by an observer.
"The two events are separated by a certain interval of time which can be measured as Jupiter moves, and compared with an independently-measured interval of time taken by photon to propagate from Jupiter to the observer. The experiment found that two intervals of time for gravity and light coincide up to 20 percent. Therefore, the gravitational field cannot act faster than light propagates."
Other physicists argue that the Fomalont-Kopeikin experiment measured nothing else but the speed of light. "This point of view stems from the belief that the time-dependent perturbation of the gravitational field of a uniformly moving Jupiter is too small to detect," Kopeikin said. "However, our research article clearly demonstrates that this belief is based on insufficient mathematical exploration of the rich nature of the Einstein field equations and a misunderstanding of the physical laws of interaction of light and gravity in curved space-time."
The research paper that discusses the gravimagnetic field appears in the October edition of Journal of General Relativity and Gravitation.
Note: This story has been adapted from material provided by University of Missouri-Columbia.

Fausto Intilla
www.oloscience.com

Breaking The Barrier Toward Nanometer X-ray Resolution

Source:

http://www.sciencedaily.com/releases/2007/09/070928160751.htm

Science Daily — A team of researchers at the U.S. Department of Energy's Brookhaven National Laboratory have overcome a major obstacle for using refractive lenses to focus x-rays. This method will allow the efficient focusing of x-rays down to extremely small spots and is an important breakthrough in the development of a new, world-leading light source facility that promises advances in nanoscience, energy, biology, and materials research.
At Brookhaven's National Synchrotron Light Source (NSLS), the scientists exceeded a limit on the ability to focus "hard," or high-energy, x-rays known as the "critical angle."
The critical angle is the maximum angle that light can be deflected, or bent, by a single surface. Imagine a beam of laser light traveling toward a glass lens. Depending on the characteristics of the lens material and the angle at which the beam is pointed, the light can be refracted, that is, transmitted through the lens but deflected. However, when this light approaches the lens at angles less than the critical angle, the beam does not pass through the lens but is instead reflected. This results in a maximum deflection angle for light that passes through the lens.
The maximum deflection angle determines the minimum spot size to which x-rays can be focused. This poses a problem for researchers who are using x-rays to study molecules, atoms, and advanced materials at the nanoscale - on the order of billionths of a meter. Such small subjects require tightly focused beams.
"One measure of the quality of an x-ray optic is how small a focused spot it can make," said NSLS researcher Ken Evans-Lutterodt. "The problem is that nature does not allow a single lens to deflect the x-rays very much. This limits how small of a spot you can create, and this translates to some fuzziness in the image. To get a sharper image, you need a lens that's more able to deflect the x-rays."
In 2003, a trio of Brookhaven researchers - Evans-Lutterodt, Aaron Stein, and James Ablett - were the first to notice the critical angle limit while investigating the properties of a so-called kinoform lens for focusing hard x-rays. This efficient type of refractive lens is similar to those found in lighthouses. The research team proposed a solution to the critical angle problem of a compound kinoform lens, and both the problem and proposed solution were also suggested later by other researchers in the field.
In the current publication, the researchers implemented their idea by creating a compound lens from a series of four kinoform lenses placed one after the other. Using this setup at NSLS beamline X13B, they showed that the critical angle can be surpassed with hard x-rays, while still focusing like a single lens.
"Thanks to the excellent fabrication resources at Brookhaven's Center for Functional Nanomaterials and at Alcatel-Lucent, we are able to fabricate the lenses to the precision required," Stein said.
This is an important step for the National Synchrotron Light Source II (NSLS-II), a state-of-the-art synchrotron facility that will produce x-rays up to 10,000 times brighter than those generated by the current NSLS and could lead to advances such as alternative-energy technologies and new drugs for fighting disease. One of the major goals of the facility is to probe materials and molecules with just one-nanometer resolution - a capability needed to study the intricate mechanisms of chemical and biological systems.
"Without exceeding the critical angle, the refractive lens resolution would be limited to 24 nanometers or more," Ablett said. "Even though in this experiment we just barely exceeded this limit, we've shown that it can be done. This is just the first step."
Next, the researchers will measure the resolution their new lens system produces, and will continue to fabricate and test optics that push further beyond the critical angle, and closer to the one-nanometer benchmark.
"We've broken the barrier, now there's still more work to be done to get down to those small x-ray spots," Evans-Lutterodt said. "Hopefully this will be one of the routes that NSLS-II and others will use."
Their results are described online in the September 28, 2007, edition of Physical Review Letters.
Natasha Bozovic, from San Jose State University, also collaborated on this research. Funding was provided by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science.
Note: This story has been adapted from material provided by DOE, Brookhaven National Laboratory.

Fausto Intilla
www.oloscience.com

'Radio Wave Cooling' Offers New Twist On Laser Cooling

Source:

http://www.sciencedaily.com/releases/2007/09/070914105600.htm

Science Daily — Visible and ultraviolet laser light has been used for years to cool trapped atoms--and more recently larger objects--by reducing the extent of their thermal motion.

Now, applying a different form of radiation for a similar purpose, physicists at the National Institute of Standards and Technology (NIST) have used radio waves to dampen the motion of a miniature mechanical oscillator containing more than a quadrillion atoms, a cooling technique that may open a new window into the quantum world using smaller and simpler equipment.
Described in a forthcoming issue of Physical Review Letters,* this demonstration of radio-frequency (RF) cooling of a relatively large object may offer a new tool for exploring the elusive boundary where the familiar rules of the everyday, macroscale world give way to the bizarre quantum behavior seen in the smallest particles of matter and light. There may be technology applications as well: the RF circuit could be made small enough to be incorporated on a chip with tiny oscillators, a focus of intensive research for use in sensors to detect, for example, molecular forces.
The NIST experiments used an RF circuit to cool a 200 x 14 x 1,500 micrometer silicon cantilever--a tiny diving board affixed at one end to a chip and similar to the tuning forks used in quartz crystal watches--vibrating at 7,000 cycles per second, its natural "resonant" frequency. Scientists cooled it from room temperature (about 23 degrees C, or 73 degrees F) to -228 C (-379 F).
Other research groups have used optical techniques to chill micro-cantilevers to lower temperatures, but the RF technique may be more practical in some cases, because the equipment is smaller and easier to fabricate and integrate into cryogenic systems. By extending the RF method to higher frequencies at cryogenic temperatures, scientists hope eventually to cool a cantilever to its "ground state" near absolute zero (-273 C or -460 F) , where it would be essentially motionless and quantum behavior should emerge.
Laser cooling is akin to using the kinetic energy of millions of ping-pong balls (particles of light) striking a rolling bowling ball (such as an atom) to slow it down. The RF cooling technique, lead author Kenton Brown says, is more like pushing a child on a swing slightly out of synch with its back-and-forth motion to reduce its arc. In the NIST experiments, the cantilever's mechanical motion is reduced by the force created between two electrically charged plates, one of which is the cantilever, which store energy like electrical capacitors.
In the absence of any movement, the force would be stable, but in this case, it is modulated by the cantilever vibrations. The stored energy takes some time to change in response to the cantilever's movement, and this delay pushes the cantilever slightly out of synch, damping its motion.
* K.R. Brown, J. Britton, R.J. Epstein, J. Chiaverini, D. Leibfried, and D.J. Wineland. 2007. Passive cooling of a micromechanical oscillator with a resonant electric circuit. Physical Review Letters. [Forthcoming].
Note: This story has been adapted from a news release issued by National Institute of Standards and Technology.

Fausto Intilla

www.oloscience.com