David Kirkpatrick

February 26, 2010

Quantum physics improving electronics and autos

Or so this news from Princeton purports.

The release:

SCIENTISTS FIND AN EQUATION FOR MATERIALS INNOVATION

Posted Feb 25, 2010By Chris Emery

Professor Emily Carter and graduate student Chen Huang developed a new way of predicting important properties of substances. The advance could speed the development of new materials and technologies. (Photo: Frank Wojciechowski)

Princeton engineers have made a breakthrough in an 80-year-old quandary in quantum physics, paving the way for the development of new materials that could make electronic devices smaller and cars more energy efficient.

By reworking a theory first proposed by physicists in the 1920s, the researchers discovered a new way to predict important characteristics of a new material before it’s been created. The new formula allows computers to model the properties of a material up to 100,000 times faster than previously possible and vastly expands the range of properties scientists can study.

“The equation scientists were using before was inefficient and consumed huge amounts of computing power, so we were limited to modeling only a few hundred atoms of a perfect material,” said Emily Carter, the engineering professor who led the project.

“But most materials aren’t perfect,” said Carter, the Arthur W. Marks ’19 Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics. “Important properties are actually determined by the flaws, but to understand those you need to look at thousands or tens of thousands of atoms so the defects are included. Using this new equation, we’ve been able to model up to a million atoms, so we get closer to the real properties of a substance.”

By offering a panoramic view of how substances behave in the real world, the theory gives scientists a tool for developing materials that can be used for designing new technologies. Car frames made from lighter, strong metal alloys, for instance, might make vehicles more energy efficient, and smaller, faster electronic devices might be produced using nanowires with diameters tens of thousands of times smaller than that of a human hair.

Paul Madden, a chemistry professor and provost of The Queen’s College at Oxford University, who originally introduced Carter to this field of research, described the work as a “significant breakthrough” that could allow researchers to substantially expand the range of materials that can be studied in this manner. “This opens up a new class of material physics problems to realistic simulation,” he said.

The new theory traces its lineage to the Thomas-Fermi equation, a concept proposed by Llewellyn Hilleth Thomas and Nobel laureate Enrico Fermi in 1927. The equation was a simple means of relating two fundamental characteristics of atoms and molecules. They theorized that the energy electrons possess as a result of their motion — electron kinetic energy — could be calculated based how the electrons are distributed in the material. Electrons that are confined to a small region have higher kinetic energy, for instance, while those spread over a large volume have lower energy.

Understanding this relationship is important because the distribution of electrons is easier to measure, while the energy of electrons is more useful in designing materials. Knowing the electron kinetic energy helps researchers determine the structure and other properties of a material, such as how it changes shape in response to physical stress. The catch was that Thomas and Fermi’s concept was based on a theoretical gas, in which the electrons are spread evenly throughout. It could not be used to predict properties of real materials, in which electron density is less uniform.

The next major advance came in 1964, when another pair of scientists, Pierre Hohenberg and Walter Kohn, another Nobel laureate, proved that the concepts proposed by Thomas and Fermi could be applied to real materials. While they didn’t derive a final, working equation for directly relating electron kinetic energy to the distribution of electrons, Hohenberg and Kohn laid the formal groundwork that proved such an equation exists. Scientists have been searching for a working theory ever since.

Carter began working on the problem in 1996 and produced a significant advance with two postdoctoral researchers in 1999, building on Hohenberg and Kohn’s work. She has continued to whittle away at the problem since. “It would be wonderful if a perfect equation that explains all of this would just fall from the sky,” she said. “But that isn’t going to happen, so we’ve kept searching for a practical solution that helps us study materials.”

In the absence of a solution, researchers have been calculating the energy of each atom from scratch to determine the properties of a substance. The laborious method bogs down the most powerful computers if more than a few hundred atoms are being considered, severely limiting the amount of a material and type of phenomena that can be studied.

Carter knew that using the concepts introduced by Thomas and Fermi would be far more efficient, because it would avoid having to process information on the state of each and every electron.

As they worked on the problem, Carter and Chen Huang, a doctoral student in physics, concluded that the key to the puzzle was addressing a disparity observed in Carter’s earlier work. Carter and her group had developed an accurate working model for predicting the kinetic energy of electrons in simple metals. But when they tried to apply the same model to semiconductors — the conductive materials used in modern electronic devices — their predictions were no longer accurate.

“We needed to find out what we were missing that made the results so different between the semiconductors and metals,” Huang said. “Then we realized that metals and semiconductors respond differently to electrical fields. Our model was missing this.”

In the end, Huang said, the solution was a compromise. “By finding an equation that worked for these two types of materials, we found a model that works for a wide range of materials.”

Their new model, published online Jan. 26 in Physical Review B, a journal of the American Physical Society, provides a practical method for predicting the kinetic energy of electrons in semiconductors from only the electron density. The research was funded by the National Science Foundation.

Coupled with advances published last year by Carter and Linda Hung, a graduate student in applied and computational mathematics, the new model extends the range of elements and quantities of material that can be accurately simulated.

The researchers hope that by moving beyond the concepts introduced by Thomas and Fermi more than 80 years ago, their work will speed future innovations. “Before people could only look at small bits of materials and perfect crystals,” Carter said. “Now we can accurately apply quantum mechanics at scales of matter never possible before.”

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December 23, 2009

Digital quantum batteries

Via KurzweilAI.net — This could be revolutionary. Wonder what a realistic time-to-market is for this concept.

A Quantum Leap in Battery Design
Technology Review, Dec. 21, 2009

A “digital quantum battery” concept proposed by a physicist at the University of Illinois at Urbana-Champaign could provide orders-of- magnitude-greater energy storage capacity.

The concept calls for billions of nanoscale capacitors and would rely on quantum effects to suppress arcing, which wastes stored power.

The digital part of the concept derives from the fact that each nanovacuum tube would be individually addressable. Because of this, the devices could perhaps be used to store data, too.
Read Original Article>>

September 18, 2009

Quantum electric motor

Filed under: Science — Tags: , , , — David Kirkpatrick @ 5:25 pm

Via KurzweilAI.net — Man that thing is cool.

Blueprint for a Quantum Electric Motor

the physics arXiv blog, Sept. 18, 2009

Two atoms trapped in a ring-shaped optical lattice driven by an alternating magnetic field can create the smallest electric motor, University of Augsburg researchers have discovered.

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September 16, 2009

Quantum creatures

Via KurzweilAI.net — This is just wild. There’s not much more to add.

Could we create quantum creatures in the lab?

NewScientist Physics & Math, Sept. 15, 2009

Two laser beams could hold a tardigrade (water bear — ananimal less than a millimeter in size that can survive in avacuum) in a “ground state” in an “optical cavity,” where a photon could force it into a superposition of both its ground state and next vibrational energy state, scientists at the Max Planck Institute for Quantum Optics suggest.

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March 3, 2009

Quantum paradox observed

Big, big news in physics.

The release:

Quantum paradox directly observed — a milestone in quantum mechanics

In quantum mechanics, a vanguard of physics where science often merges into philosophy, much of our understanding is based on conjecture and probabilities, but a group of researchers in Japan has moved one of the fundamental paradoxes in quantum mechanics into the lab for experimentation and observed some of the ‘spooky action of quantum mechanics’ directly.

Hardy’s Paradox, the axiom that we cannot make inferences about past events that haven’t been directly observed while also acknowledging that the very act of observation affects the reality we seek to unearth, poses a conundrum that quantum physicists have sought to overcome for decades. How do you observe quantum mechanics, atomic and sub-atomic systems that are so small-scale they cannot be described in classical terms, when the act of looking at them changes them permanently?

In a journal paper published in the New Journal of Physics, ‘Direct observation of Hardy’s paradox by joint weak measurement with an entangled photon pair’, today, Wednesday, 4 March, authored by Kazuhiro Yokota, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto from the Graduate School of Engineering Science at Osaka University and the CREST Photonic Quantum Information Project in Kawaguchi City, the research group explains how they used a measurement technique that has an almost imperceptible impact on the experiment which allows the researchers to compile objectively provable results at sub-atomic scales.

The experiment, based on Lucien Hardy’s thought experiment, which follows the paths of two photons using interferometers, instruments that can be used to interfere photons together, is believed to throw up contradictory results that do not conform to our classical understanding of reality. Although Hardy’s Paradox is rarely refuted, it was only a thought experiment until recently.

Using an entangled pair of photons and an original but complicated method of weak measurement that does not interfere with the path of the photons, a significant step towards harnessing the reality of quantum mechanics has been taken by these researchers in Japan.

As the researchers write, “Unlike Hardy’s original argument, our demonstration reveals the paradox by observation, rather than inference. We believe the demonstrated joint weak measurement is useful not only for exploiting fundamental quantum physics, but also for various applications such as quantum metrology and quantum information technology.”

 

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August 14, 2008

Busting the speed of light

Filed under: Science — Tags: , , , , , — David Kirkpatrick @ 12:17 pm

Interesting news from KurzweilAI.net:

Quantum strangeness breaks the light barrier
New Scientist, Aug. 13, 2008

University of Geneva scientists sent pairs of entangled photons to labs 18 kilometers apart, showing that if superluminal signals are responsible for entanglement, they must travel at more than 10,000 times the speed of light.

 
Read Original Article>>

July 30, 2008

Life imitates art — the Matrix

Filed under: Science — Tags: , , — David Kirkpatrick @ 2:02 pm

From KurzweilAI.net:

Building ‘The Matrix’
Science News, July 27th, 2008

Physicists at the Max Planck Institute for Quantum Optics have created a rudimentary prototype of a machine that simulates quantum phenomena using quantum physics, rather than using data kept in a classical computer.

It demonstrates a technique that could enable physicists to create, in the virtual world, materials that don’t yet exist in nature and perhaps figure out how to build, in the real world, superconductors that work at room temperature, for example.

 
Read Original Article>>

June 26, 2008

Quantum images

From KurzweilAI.net:

Physicists Produce Quantum-Entangled Images
PhysOrg.com, June 25, 2008

Researchers from the National Institute of Standards and Technology (NIST) and the University of Maryland (UM) have produced “quantum images,” pairs of information-rich visual patterns whose features are entangled (linked by the laws of quantum physics).


(NIST)

Matching up both quantum images and subtracting their fluctuations, their noise is lower (so their information content potentially higher) than it is from any two classical images.

In addition to promising better detection of faint objects and improved amplification and positioning of light beams, the researchers’ technique for producing quantum images may someday be useful for storing patterns of data in quantum computers and transmitting large amounts of highly secure encrypted information.
 
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