Nanocarros

Synthesis and Single-Molecule Imaging of Highly Mobile Adamantane-Wheeled Nanocars

• pubs.acs.org
• Author Of
• November 27th, 2012

The synthesis and single-molecule imaging of two inherently fluorescent nanocars equipped with adamantane wheels is reported. The nanocars were imaged using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as the chromophore, which was rigidly incorporated into the nanocar chassis via Sonogashira cross-coupling chemistry that permitted the synthesis of nanocars having different geometries. In particular, studied here were four- and three-wheeled nanocars with adamantane wheels. It was found that, for the four-wheeled nanocar, the percentage of moving nanocars and the diffusion constant show a significant improvement overp-carborane-wheeled nanocars with the same chassis. The three-wheeled nanocar showed only limited mobility due to its geometry. These results are consistent with a requisite wheel-like rolling motion. We furthermore developed a model that relates the percentage of moving nanocars in single-molecule experiments with the diffusion constant. The excellent agreement between the model and the new results presented here as well as previous single-molecule studies of fluorescent nanocars yields an improved understanding of motion in these molecular machines.

Energía solar más eficiente.

From icy water to steam via nanoparticles

• futurity.org
• Jade Boyd-rice
• November 19th, 2012
• view original

New technology that uses nanoparticles to convert solar energy directly into steam is about "a lot more than electricity," says Naomi Halas of the Laboratory for Nanophotonics at Rice University. "With this technology, we are beginning to think about solar thermal power in a completely different way." (Credit:

The solar steam method has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency around 15 percent. Inventors of solar steam expect the first uses of the new technology won’t be for electricity generation but rather for sanitation and water purification in developing countries.

“This is about a lot more than electricity,” says Naomi Halas of the Laboratory for Nanophotonics at Rice University. “With this technology, we are beginning to think about solar thermal power in a completely different way.”

Straight from the Source

Read the original study

DOI: 10.1021/nn304948h

As reported in ACS Nano, the efficiency of solar steam is due to the light-capturing nanoparticles that convert sunlight into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. Halas says the solar steam’s overall energy efficiency can probably be increased as the technology is refined.

“We’re going from heating water on the macro scale to heating it at the nanoscale,” Halas says. “Our particles are very small—even smaller than a wavelength of light—which means they have an extremely small surface area to dissipate heat. This intense heating allows us to generate steam locally, right at the surface of the particle, and the idea of generating steam locally is really counterintuitive.”

To show just how counterintuitive, Rice graduate student Oara Neumann videotaped a solar steam demonstration in which a test tube of water containing light-activated nanoparticles was submerged into a bath of ice water. Using a lens to concentrate sunlight onto the near-freezing mixture in the tube, Neumann showed she could create steam from nearly frozen water.

Steam is one of the world’s most-used industrial fluids. About 90 percent of electricity is produced from steam, and steam is also used to sterilize medical waste and surgical instruments, to prepare food, and to purify water.

Most industrial steam is produced in large boilers—solar steam’s efficiency could allow it to become economical on a much smaller scale.

People in developing countries will be among the first to see the benefits of solar steam. Rice engineering undergraduates have already created a solar steam-powered autoclave that’s capable of sterilizing medical and dental instruments at clinics that lack electricity. Halas also won a Grand Challenges grant from the Bill and Melinda Gates Foundation to create an ultra-small-scale system for treating human waste in areas without sewer systems or electricity.

“Solar steam is remarkable because of its efficiency,” says Neumann, the lead co-author on the paper. “It does not require acres of mirrors or solar panels. In fact, the footprint can be very small. For example, the light window in our demonstration autoclave was just a few square centimeters.”

Another potential use could be in powering hybrid air-conditioning and heating systems that run off of sunlight during the day and electricity at night. Halas, Neumann, and colleagues have also conducted distillation experiments and found that solar steam is about two-and-a-half times more efficient than existing distillation columns.

Halas, a professor in electrical and computer engineering and of physics, chemistry, and biomedical engineering, specializes in creating and studying light-activated particles. One of her creations, gold nanoshells, is the subject of several clinical trials for cancer treatment.

For the cancer treatment technology and many other applications, Halas’ team chooses particles that interact with just a few wavelengths of light. For the solar steam project, Halas and Neumann set out to design a particle that would interact with the widest possible spectrum of sunlight energy. Their new nanoparticles are activated by both visible sunlight and shorter wavelengths that humans cannot see.

“We’re not changing any of the laws of thermodynamics,” Halas says. “We’re just boiling water in a radically different way.”

The research was supported by the Welch Foundation and the Bill and Melinda Gates Foundation.

Source: Rice University

Utilizar la energía de los cambios de temperatura.

Scientists use nanotechnology to harvest electricity from temperature fluctuations

• engadget.com
• Steve Dent
• November 21st, 2012
• view original

So far your footsteps, breath and nervous energy have all been tapped to charge up batteries, and now researchers from the Georgia Institute of Technology scientists have pulled it off using thermal changes. They did it with so-called pyroelectric nanogenerators, which use polarization changes to harvest heat energy from temperature fluctuations. Normally output current is too low for commercial electronics, but by making one with lead zirconate titanate (PZT), the team was able to create a device that could charge a Li-ion coin battery to power a green LED for a few seconds. The researchers predict that by doubling the surface area, they could drive wireless sensors or LCDs using only environmental temperature changes from an engine or water pipe, for instance. The result could be green power, but without all that pesky moving around.

Teletransportación cuántica entre dos objetos macroscópicos.

Researchers Achieve Quantum Teleportation Between Two Macroscopic Objects For The First Time

• popsci.com
• Clay Dillow
• November 12th, 2012

Quantum Teleportation Explained In case you want to try this at home.

Sometimes it’s tough to get excited about stuff happening in quantum technologies, not because it’s anything less than fascinating but because it can be so hard to wrap your head around this stuff and anyhow the practical applications often seem very far away. But this is one of those milestones that you have to appreciate: Physicists have for the first time teleported quantum information from one macroscopic object to another.

Researchers have been able to teleport quantum information for a while now. Quick quantum primer: This isn’t Star Trek-style teleportation, but the transfer of information--of quantum states--from one place to another without that information crossing the space between them in any way. This is achieved through the strange quantum phenomenon of entanglement, which allows two quantum objects to share the same quantum state such that if you influence one particle you also influence the other, whether they are separated by nanometers or light-years.

So by entangling two photons, for instance, physicists have demonstrated the ability to transmit quantum information from one place to another by encoding it in these quantum states--influence one of the pair and a change can be measured in the other without any information actually passing between the two. Researchers have done this before, between photons, between ions, and even between a macroscopic object and a microscopic object. But now Chinese researchers have, for the first time, achieved quantum teleportation between two macroscopic objects across nearly 500 feet using entangled photons.

That’s pretty huge. The two bundles of rubidium atoms that served as sender and receiver are more or less analogs for what we hope will someday be our “quantum Internet”--a system of routers like the ones we have now that, instead of beaming information around a vast network of fiber optic wires, will send and receive information through entangled photons. So in a way, this is like a first proof of concept, evidence that the idea works at least in the lab.

Now all we have to do is figure out is how to build several of these in series so they can actually pass information from one to the other. To do that, we only have to somehow force these quantum states to exist for longer than the hundred microseconds or so that they last now before degrading. Sounds easy enough.

Grafeno en circuitos.

Light up graphene for circuits on demand

• futurity.org
• Mike Williams-rice
• October 10th, 2012
• view original

"The doping of graphene is a key parameter in the development of graphene electronics," says Peter Nordlander. "You can't buy graphene-based electronic devices now, but there's no question that manufacturers are putting a lot of effort into it because of its potential high speed."Photo by: Credit: iStockphoto

The approach could facilitate the instant creation of circuitry—optically induced electronics—on graphene patterned with plasmonic antennas that can manipulate light and inject electrons into the material to affect its conductivity.

The research incorporates both theoretical and experimental work to show the potential for making simple, graphene-based diodes and transistors on demand. Their breakthrough is reported in the journal ACS Nano.

Nanoscale plasmonic antennas called nonamers placed on graphene have the potential to create electronic circuits by hitting them with light at particular frequencies, according to researchers at Rice University. The positively and negatively doped graphene can be prompted to form phantom circuits on demand. (Credit: Rice University)

Nonamers in the drawings at top and in the photos at bottom are arrays of nine gold nanoparticles deposited on graphene and tuned to particular frequencies of light. When illuminated, the plasmonic particles pump electrons into the graphene, according to researchers at Rice University who say the technology may lead to the creation of on-demand circuitry for electronic devices. (Credit: Rice University)

Straight from the Source

Read the original study

DOI: 10.1021/nn304028b

“One of the major justifications for graphene research has always been about the electronics,” says Peter Nordlander, professor of physics and astronomy and of electrical and computer engineering at Rice University. “People who know silicon understand that electronics are only possible because it can be p- and n-doped (positive and negative), and we’re learning how this can be done on graphene.

“The doping of graphene is a key parameter in the development of graphene electronics,” he adds. “You can’t buy graphene-based electronic devices now, but there’s no question that manufacturers are putting a lot of effort into it because of its potential high speed.”

Researchers have investigated many strategies for doping graphene, including attaching organic or metallic molecules to its hexagonal lattice. Making it selectively—and reversibly—amenable to doping would be like having a graphene blackboard upon which circuitry can be written and erased at will, depending on the colors, angles, or polarization of the light hitting it.

The ability to attach plasmonic nanoantennas to graphene affords just such a possibility.

Nordlander and colleague Naomi Halas, a professor at Rice, have considerable expertise in the manipulation of the quasiparticles known as plasmons, which can be prompted to oscillate on the surface of a metal.

In earlier work, they succeeded in depositing plasmonic nanoparticles that act as photodetectors on graphene.

These metal particles don’t so much reflect light as redirect its energy; the plasmons that flow in waves across the surface when excited emit light or can create “hot electrons” at particular, controllable wavelengths. Adjacent plasmonic particles can interact with each other in ways that are also tunable.

That effect can easily be seen in graphs of the material’s Fano resonance, where the plasmonic antennas called nonamers, each a little more than 300 nanometers across, clearly scatter light from a laser source except at the specific wavelength to which the antennas are tuned.

For the Rice experiment, those nonamers—eight nanoscale gold discs arrayed around one larger disc—were deposited onto a sheet of graphene through electron-beam lithography. The nonamers were tuned to scatter light between 500 and 1,250 nanometers, but with destructive interference at about 825 nanometers.

At the point of destructive interference, most of the incident light energy is converted into hot electrons that transfer directly to the graphene sheet and change portions of the sheet from a conductor to an n-doped semiconductor.

Arrays of antennas can be affected in various ways and allow phantom circuits to materialize under the influence of light.

“Quantum dot and plasmonic nanoparticle antennas can be tuned to respond to pretty much any color in the visible spectrum,” Nordlander says. “We can even tune them to different polarization states, or the shape of a wavefront.

“That’s the magic of plasmonics,” he adds. “We can tune the plasmon resonance any way we want. In this case, we decided to do it at 825 nanometers because that is in the middle of the spectral range of our available light sources. We wanted to know that we could send light at different colors and see no effect, and at that particular color see a big effect.”

Nordlander says he foresees a day when, instead of using a key, people might wave a flashlight in a particular pattern to open a door by inducing the circuitry of a lock on demand.

“Opening a lock becomes a direct event because we are sending the right lights toward the substrate and creating the integrated circuits. It will only answer to my call,” he explains.

The Robert A. Welch Foundation, the Office of Naval Research, the Department of Defense National Security Science and Engineering Faculty Fellows program, and Fundacio Cellex Barcelona funded the work.

Source: Rice University

Sensor con color.

‘Nano-pancake’ sensor warns with color

• futurity.org
• Mike Williams-rice
• October 10th, 2012
• view original

The researchers progressively turned a clear film bluePhoto by: with thiocyanate

The new work led by Rice University materials scientist Ned Thomas combines polymers into a unique, self-assembled metamaterial that, when exposed to ions in a solution or in the environment, changes color depending on the ions’ ability to infiltrate the hydrophilic (water-loving) layers. Possible applications include multiband optical elements in laser-driven systems, and as part of high-contrast displays.

The micron-thick material called a photonic gel, far thinner than a human hair, is so inexpensive to make that, Thomas says, “We could cover an area the size of a football field with this film for about a hundred dollars.”

Alternating, nano-sized layers of hydrophilic and hydrophobic molecules self-assemble into a block copolymer called a photonic gel. It changes color depending on the amount of water absorbed by the hydrophilic layers, which can be tuned by the solvent used. (Credit: Thomas Lab/Rice)

Straight from the Source

Read the original study

DOI: 10.1021/nn302949n

But for practical applications, much smaller pieces would do. “Suppose you want a food sensor,” says Thomas, dean of Rice’s George R. Brown School of Engineering and former chair of the department of materials science and engineering at MIT.

“If it’s inside a sealed package and the environment in that package changes because of contamination or aging or exposure to temperature, an inspector would see that sensor change from blue to red and know immediately the food is spoiled.”

Such visual cues are good, he says, “especially when you need to look at a lot of them. And you can read these sensors with low tech, either with your own eyes or a spectrophotometer to scan things.”

As reported in the American Chemical Society journal ACS Nano, the films are made of nanoscale layers of hydrophobic polystyrene and hydrophilic poly (2-vinyl pyridine). In the liquid solution, the polymer molecules are diffused, but when the liquid is applied to a surface and the solvent evaporates, the block copolymer molecules self-assemble into a layered structure.

The polystyrene molecules clump together to keep water molecules out, while the poly (2-vinyl pyridine), P2VP for short, forms its own layers between the polystyrene. On a substrate, the layers form into a transparent stack of alternating “nano-pancakes.”

“The beauty of self-assembly is that it’s simultaneous, all the layers forming at once,” Thomas says.

Researchers pu a photonic gel through a series of color changes by repeatedly washing it and exposing it to new compounds. (Credit: Thomas Lab/Rice University)

Reversible spectrum

The researchers exposed their films to various solutions and found different colors depending on how much solvent was taken up by the P2VP layers. For example with a chlorine/oxide/iron solution that is not readily absorbed by the P2VP, the film is transparent, Thomas says. “When we take that out, wash the film and bring in a new solution with a different ion, the color changes.”

The researchers progressively turned a clear film to blue (with thiocyanate), to green (iodine), to yellow (nitrate), to orange (bromine), and finally to red (chlorine). In each case, the changes were reversible.

Thomas explained that the direct exchange of counterions from the solution to the P2VP expands those layers and creates a photonic band gap—the light equivalent of a semiconducting band gap—that allows color in a specific wavelength to be reflected. “The wavelengths in that photonic band gap are forbidden to propagate,” he says, which allows the gels to be tuned to react in specific ways.

“Imagine a solid in which you create a band gap everywhere but along a 3D path, and let’s say that path is a narrowly defined region you can fabricate within this otherwise photonic material. Once you put light in that path, it is forbidden to leave because it can’t enter the material, due to the band gap.

“This is called molding the flow of light,” he says. “These days in photonics, people are thinking about light as though it were water. That is, you can put it in these tiny pipes. You can turn light around corners that are very sharp. You can put it where you want it, keep it from where you don’t want it. The plumbing of light has been much easier than in the past, due to photonics, and in photonic crystals, due to band gaps.”

The US Army Research Office, the US Air Force, and the Korea Research Foundation, funded by the Korean government, supported the research.

Source: Rice University

El grafeno para la corrosión.

Graphene coating stops corrosion 100x better

• futurity.org
• Emily Walker-monash
• October 4th, 2012
• view original

The polymer coatings that are often used on metals can be scratched, compromising their protective ability, but the invisible layer of graphene—although it changes neither the feel nor the appearance of the metal—is much harder to damage.Photo by: Credit: "graphene illustration" via Shutterstock

In a paper published in the September issue of Carbon, researchers from Monash University and Rice University say their findings could mean paradigm changes in the development of anti-corrosion coatings.

Graphene is a microscopically thin layer of carbon atoms. It is already in use in such things as smartphone screens, and is attracting research attention for its possibilities as a means of increasing metal’s resistance to corrosion.

Straight from the Source

Read the original study

DOI: 10.1016/j.carbon.2012.04.048

“We have obtained one of the best improvements that have been reported so far,” says study co-author Mainak Majumder. “At this point we are almost 100 times better than untreated copper. Other people are maybe five or six times better, so it’s a pretty big jump.”

Parama Banerjee, who performed most of the experiments for this study, says graphene had excellent mechanical properties and great strength.

The polymer coatings that are often used on metals can be scratched, compromising their protective ability, but the invisible layer of graphene—although it changes neither the feel nor the appearance of the metal—is much harder to damage.

“I call it a magic material,” Banerjee says.

The researchers applied the graphene to copper at temperatures between 800 and 900 degrees, using a technique known as chemical vapour deposition, and tested it in saline water.

“In nations like Australia, where we are surrounded by ocean, it is particularly significant that such an atomically thin coating can provide protection in that environment,” notes Banerjee.

Initial experiments were confined to copper, but according to Banerjee research was already under way on using the same technique with other metals.

This would open up uses for a huge range of applications, from ocean-going vessels to electronics: anywhere that metal is used and at risk of corrosion. Such a dramatic extension of metal’s useful life could mean tremendous cost savings for many industries.

The process is still in the laboratory-testing stage, but Majumder says the group was not only looking at different metals, but also investigating ways of applying the coating at lower temperatures, which would simplify production and enhance market potential.

Source: Monash University

Analisis en nanoescala

Nano-scale analysis without the destruction

• futurity.org
• Paul Mannion-sheffield
• August 27th, 2012

Previously, structural analysis destroyed whatever nanomaterial scientists examined. "This limitation is now overcome by our new techniques, which rely on inherently non-invasive nuclear magnetic resonancePhoto by: NMR

The nuclear magnetic resonance apparatus—developed by the University of Sheffield department of physics and astronomy—will allow for further developments and new applications for nanotechnology which is increasingly used in harvesting solar energy, computing, communication developments, and also in the medical field.

Their findings are published in Nature Nanotechnology.

Straight from the Source

Read the original study

DOI: 10.1038/nnano.2012.142

Alexander Tartakovskii, who led the team of researchers, says: “We have developed a new important tool for microscopy analysis of nanostructures. The very tiny quantities of matter used in nanostructures—the behavior of electrons and photons—is governed by new quantum effects, quite different from what happens in bulk materials.

“Development requires careful structural analysis, in order to understand how the nanostructures are formed, and how we can build them to enhance and control their useful properties.

“Existing structural analysis methods, key for the research and development of new materials, are invasive: a nanostructure would be irreversibly destroyed in the process of the experiment, and, as a result, the important link between the structural and electronic or photonic properties would usually be lost.

“This limitation is now overcome by our new techniques, which rely on inherently non-invasive nuclear magnetic resonance (NMR) probing.”

The results open a new way of nano-engineering, a full characterization of a new material and new semiconductor nano-device without destroying them meaning more research and development and device fabrication processes.

Tarakovskii adds: “We have developed new techniques which allowed unprecedented sensitivity and enhancement of the NMR signal in nanostructures. Particular nanostructures of interest in our research are semiconductor quantum dots, which are researched widely for their promising photonic applications, and potential for the use in a new type of computer hardware employing quantum logic.

“The result of our experiments was quite unexpected and changed our understanding of the architecture of these nanomaterials: we learned new information about the chemical composition of quantum dots, and also how atom alignment inside the dots deviates from that of a perfect crystal.

“Importantly, many more measurements of optical and magnetic properties can be done on the same quantum dots which have undergone the NMR probing.”

The development of the new techniques and all experimental work was carried out by Evgeny Chekhovich in Tartakovskii’s group. Quantum dot samples used in this work have also been fabricated in Sheffield, in the EPSRC National Facility for III-V Semiconductor Technology.

Source: University of Sheffield

http://www.futurity.org/science-technology/nano-scale-analysis-without-the-destruction/

Gerardo Partida Guzmán

 

Chip 3D

Globalfoundries unveils 14nm-XM chip architecture, vows up to a 60 percent jump in battery life

Jon Fingas

Globalfoundries wants to show that it can play the 3D transistor game as well as Intel. Its newly unveiled 14nm-XM (Extreme Mobility) modular architecture uses the inherently low-voltage, low-leak nature of the foundry's FinFET layout, along with a few traces of its still-in-development 20nm process, to build a 14-nanometer chip with all the size and power savings that usually come from a die shrink. Compared to the larger processors with flat transistors that we're used to, the new technique is poised to offer between 40 to 60 percent better battery life, all else being equal -- a huge help when even those devices built on a 28nm Snapdragon S4 can struggle to make it through a full day on a charge. To no one's shock, Globalfoundries is focusing its energy on getting 14nm-XM into the ARM-based processors that could use the energy savings the most. It will be some time before you find that extra-dimensional technology sitting in your phone or tablet, though. Just as Intel doesn't expect to reach those miniscule sizes until 2013, Globalfoundries expects its first working 14nm silicon to arrive the same year. That could leave a long wait between test production runs and having a finished product in your hands.

Fuente:

http://www.engadget.com/2012/09/23/globalfoundries-unveils-14nm-xm-chip-architecture/

Gerardo Partida Guzmán

Rayo de traccón

Good vibrations

Wednesday, August 15, 2012

In-depth R&D news and innovations - Sign up now!

click to enlarge Berkeley Lab researchers directly observed quantum optical effects—amplification and ponderomotive squeezing—in an optomechanical system. Here the yellow/red regions show amplification, the blue regions show squeezing. On the left is the data, on the right is the theoretical prediction in the absence of noise. Image: Stamper-Kurn group

A long-time staple of science fiction is the tractor beam, a technology in which light is used to move massive objects—recall the tractor beam in the movie Star Wars that captured the Millennium Falcon and pulled it into the Death Star. While tractor beams of this sort remain science fiction, beams of light today are being used to mechanically manipulate atoms or tiny glass beads, with rapid progress being made to control increasingly larger objects. Those who see major roles for optomechanical systems in a host of future technologies will take heart in the latest results from a first-of-its-kind experiment.

Scientists with the U.S. Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, using a unique optical trapping system that provides ensembles of ultracold atoms, have recorded the first direct observations of distinctly quantum optical effects—amplification and squeezing—in an optomechanical system. Their findings point the way toward low-power quantum optical devices and enhanced detection of gravitational waves among other possibilities.

"We've shown for the first time that the quantum fluctuations in a light field are responsible for driving the motions of objects much larger than an electron and could in principle drive the motion of really large objects," says Daniel Brooks, a scientist with Berkeley Lab's Materials Sciences Division and UC Berkeley's Physics Department.

Brooks, a member of Dan Stamper-Kurn's research group, is the corresponding author of a paper in Naturedescribing this research. The paper is titled "Nonclassical light generated by quantum-noise-driven cavity optomechanics." Coauthors were Thierry Botter, Sydney Schreppler, Thomas Purdy, Nathan Brahms, and Stamper-Kurn.

Light will build up inside of an optical cavity at specific resonant frequencies, similar to how a held-down guitar string only vibrates to produce specific tones. Positioning a mechanical resonator inside the cavity changes the resonance frequency for light passing through, much as sliding one's fingers up and down a guitar string changes its vibrational tones. Meanwhile, as light passes through the optical cavity, it acts like a tiny tractor beam, pushing and pulling on the mechanical resonator.

click to enlarge (Clockwise) Nathan Brahms, Dan Brooks, Dan Stamper-Kurn, and Thierry Botter used their unique ultracold atoms laser system to record the first direct observation of distinctly quantum effects in an optomechanical system. Photo: Roy Kaltschmidt

If an optical cavity is of ultrahigh quality and the mechanical resonator element within is atomic-sized and chilled to nearly absolute zero, the resulting cavity optomechanical system can be used to detect even the slightest mechanical motion. Likewise, even the tiniest fluctuations in the light/vacuum can cause the atoms to wiggle. Changes to the light can provide control over that atomic motion. This not only opens the door to fundamental studies of quantum mechanics that could tell us more about the classical world we humans inhabit, but also to quantum information processing, ultrasensitive force sensors, and other technologies that might seem like science fiction today.

"There have been proposals to use optomechanical devices as transducers, for example coupling motion to both microwaves and optical frequency light, where one could convert photons from one frequency range to the other," Brooks says. "There have also been proposals for slowing or storing light in the mechanical degrees of freedom, the equivalent of electromagnetically induced transparency or EIT, where a photon is stored within the internal degrees of freedom."

Already cavity optomechanics has led to applications such as the cooling of objects to their motional ground state, and detections of force and motion on the attometer scale. However, in studying interactions between light and mechanical motion, it has been a major challenge to distinguish those effects that are distinctly quantum from those that are classical—a distinction critical to the future exploitation of optomechanics.

Brooks, Stamper-Kurn, and their colleagues were able to meet the challenge with their microfabricated atom-chip system which provides a magnetic trap for capturing a gas made up of thousands of ultracold atoms. This ensemble of ultracold atoms is then transferred into an optical cavity (Fabry-Pferot) where it is trapped in a one-dimensional optical lattice formed by near-infrared (850-nm wavelength) light that resonates with the cavity. A second beam of light is used for the pump/probe.

"Integrating trapped ensembles of ultracold atoms and high-finesse cavities with an atom chip allowed us to study and control the classical and quantum interactions between photons and the internal/external degrees of freedom of the atom ensemble," Brooks says. "In contrast to typical solid-state mechanical systems, our optically levitated ensemble of ultracold atoms is isolated from its environment, causing its motion to be driven predominantly by quantum radiation-pressure fluctuations."

The Berkeley research team first applied classical light modulation to a low-powered pump/probe beam (36 picoWatts) entering their optical cavity to demonstrate that their system behaves as a high-gain parametric optomechanical amplifier. They then extinguished the classical drive and mapped the response to the fluctuations of the vacuum. This enabled them to observe light being squeezed by its interaction with the vibrating ensemble and the atomic motion driven by the light's quantum fluctuations. Amplification and this squeezing interaction, which is called "ponderomotive force," have been long-sought goals of optomechanics research.

click to enlarge Dan Stamper-Kurn’s research group has developed a microfabricated atom-chip system which provides a magnetic trap for capturing a gas made up of thousands of ultracold atoms. Image: Stamper-Kurn group

"Parametric amplification typically requires a lot of power in the optical pump but the small mass of our ensemble required very few photons to turn the interactions on/off," Brooks says. "The ponderomotive squeezing we saw, while narrow in frequency, was a natural consequence of having radiation-pressure shot noise dominate in our system."

Since squeezing light improves the sensitivity of gravitational wave detectors, the ponderomotive squeezing effects observed by Brooks, Stamper-Kern, and their colleagues could play a role in future detectors. The idea behind gravitational wave detection is that a ripple in the local curvature of spacetime caused by a passing gravitational wave will modify the resonant frequency of an optical cavity which, in turn, will alter the cavity’s optical signal.

"Currently, squeezing light over a wide range of frequencies is desirable as scientists search for the first detection of a gravitational wave," Brooks explains. "Ponderomotive squeezing, should be valuable later when specific signals want to be studied in detail by improving the signal-to-noise ratio in the specific frequency range of interest."

The results of this study differ significantly from standard linear model predictions. This suggests that a nonlinear optomechanical theory is required to account for the Berkeley team's observations that optomechanical interactions generate non-classical light. Stamper-Kern's research group is now considering further experiments involving two ensembles of ultracold atoms inside the optical cavity.

"The squeezing signal we observe is quite small when we detect the suppression of quantum fluctuations outside the cavity, yet the suppression of these fluctuations should be very large inside the cavity," Brooks says. "With a two ensemble configuration, one ensemble would be responsible for the optomechanical interaction to squeeze the radiation-pressure fluctuations and the second ensemble would be studied to measure the squeezing inside the cavity."

http://www.rdmag.com/News/2012/08/General-Science-Good-Vibrations/

Gerardo Partida Guzmán