In the quantum world, photons and electrons dance, bump and carry out transactions that govern everything we see in the world around us. In this week's issue of Science, French and U.S. scientists describe a new technique in nanotechnology that allowed them to zoom in -- way in -- and observe those quantum transactions on a single DNA-sized carbon molecule called a nanotube.
The team, led by Rice University chemist Bruce Weisman and University of Bordeaux physicist Laurent Cognet, focused on short-lived quantum oddities called "excitons," which are created when light hits a semiconductor.
"Excitons in carbon nanotubes only last about 100 trillionths of a second," Weisman said. "They wink out of existence when the nanotube emits a photon of fluorescent light, but during their short lifetimes they can move around."
To study exciton mobility on nanotubes, Cognet and his co-workers conducted experiments during a sabbatical visit to Weisman's lab at Rice in early 2007. They used a fluorescence microscope to observe tiny sections of individual nanotubes less than a micrometer long. The nanotubes were held still in a soft liquid gel. By shining light on them while introducing acids and other chemicals into the gel, the team was able to observe reactions that would quench, or kill, any passing excitons. To do this, they used a time-lapse infrared camera to capture the fluorescent glow from the nanotube about 20 times a second. They then compiled records that revealed the characteristic steps that are the signature of exciton quenching by single molecules.
"We found that each nanotube exciton travels about 90 nanometers and visits some 10,000 carbon atoms during its lifespan," Cognet said.
Excitons are "quasiparticles" created when a photon strikes a semiconductor and excites an electron to a higher energy level. The electron leaves behind a positively charged void called a "hole." That hole pairs with the electron to form the exciton, which takes on a life of its own that ends abruptly when it emits a photon or becomes quenched.
Cognet said the unusual electronic properties of carbon nanotubes made them a unique system to observe single-molecule reactions.
"Nanotubes provided us a very stable baseline for our measurements," he said. "No other light-emitting molecules have the properties that we needed for this experiment."
Weisman helped found the field of nanotube spectroscopy with the 2002 discovery of nanotube fluorescence and subsequent research that classified the light signatures of dozens of types of semiconducting nanotubes.
"I was impressed at the speed and quality of the work that Dr. Cognet and the team produced during this project," said Weisman, professor of chemistry. "His visit to Rice has been extremely productive."
Quantum Bit (qubit) Circuit NEC Corporation, Japan Science and Technology Agency (JST) and the Institute of Physical and Chemical Research (RIKEN) have together successfully demonstrated the world's first quantum bit (qubit) circuit that can control the strength of coupling between qubits. Technology achieving control of the coupling strength between qubits is vital to the realization of a practical quantum computer, and has been long awaited in the scientific field.
Spintronics Technology In 1994, Bandyopadhyay and colleagues were the first group to propose the use of spin in classical computing. Then two years later, they were among the first researchers to propose the use of spin in quantum computing. The recent work goes a long way toward implementing some of these ideas.
Center for Extreme Quantum Information Theory (xQIT) The new center enables a major new push by MIT theorists in the international race to determine the ultimate capabilities of quantum information systems. Establishing these theoretical capabilities would be a step towards being able to exploit quantum effects for novel applications, including computers, communication networks and global positioning systems.
Designing Quantum Computers As if building a computer out of rubidium atoms and laser beams weren’t difficult enough, scientists sometimes have to work as if blindfolded: The quirks of quantum physics can cause correlations between the atoms to fade from view at crucial times.
Quantum Computer Demonstrated Quantum computing offers the potential to create value in areas where problems or requirements exceed the capability of digital computing, the company said. But D-Wave explains that its new device is intended as a complement to conventional computers, to augment existing machines and their market, not as a replacement for them.
Quantum Computing Breakthrough "Our work represents a breakthrough in the search for a nanoscopic [atomic scale] mechanism that could be used for a data readout device," says Christoph Boehme, assistant professor of physics at the University of Utah. "We have demonstrated experimentally that the nuclear spin orientation of phosphorus atoms embedded in silicon can be measured by very subtle electric currents passing through the phosphorus atoms."
Research: Ion Trap Physicists at the National Institute of Standards and Technology (NIST) have designed and built a novel electromagnetic trap for ions that could be easily mass produced to potentially make quantum computers large enough for practical use. The new trap, described in the June 30 issue of Physical Review Letters,* may help scientists surmount what is currently the most significant barrier to building a working quantum computer—scaling up components and processes that have been successfully demonstrated individually.
Information Processing In the drive to understand and harness quantum effects as they relate to information processing, scientists in Waterloo and Massachusetts have benchmarked quantum control methods on a 12-Qubit system. Their research was performed on the largest quantum information processor to date.
A Quantum Computer, One Dot at a Time Quantum computers do not yet exist, but it is known that they can bypass all known encryption schemes used today on the Internet. Quantum computers also are capable of efficiently solving the most important equation in quantum physics: the Schrödinger equation, which describes the time-dependence of quantum mechanical systems. Hence, if quantum computers can be built, they likely will have as large an impact on technology as the transistor.
Better Memory with Quantum Computer Bits Physicists at the National Institute of Standards and Technology (NIST) have used charged atoms (ions) to demonstrate a quantum physics version of computer memory lasting longer than 10 seconds—more than 100,000 times longer than in previous experiments on the same ions. The advance improves prospects for making practical, reliable quantum computers (which make use of the properties of quantum systems rather than transistors for performing calculations or storing information). Quantum computers, if they can be built, could break today’s best encryption systems, accelerate database searching, develop novel products such as fraud-proof digital signatures or simulate complex biological systems to help design new drugs.
Recent discoveries regarding the physics of ceramic superconductors may help improve scientists' understanding of resistance-free electrical power.
Tiny, isolated patches of superconductivity exist within these substances at higher temperatures than previously were known, according to a paper by Princeton scientists, who have developed new techniques to image superconducting behavior at the nanoscale.
Physicists at the National Institute of Standards and Technology (NIST) have demonstrated a novel way of making atoms interfere with each other, recreating a famous experiment originally done with light while also making the atoms do things that light just won’t do. Their experiments showcase some of the extraordinary behavior taken for granted in the quantum world—atoms acting like waves and appearing in two places at once, for starters—and demonstrate a new technique that could be useful in quantum computing with neutral atoms and further studies of atomic hijinks.
Better magnetic storage devices for computers and other electronics could result from new work by researchers in the United States and Germany.
Their findings demonstrate that chirality – a spiral-like "handedness" – in nanoscale magnets may play a crucial role in data transmission and manipulation in spintronic devices, where the spin rather than the charge of an electron is used to store data.