 |
|
NRL researchers develop optical technique for controlling electron spins in quantum dot ensembles
November 16, 2007Scientists are closer to developing novel devices for optics-based quantum computing and quantum information processing, as a result of a breakthrough in understanding how to make all the spins in an ensemble of quantum dots identical. This understanding, based upon a new optical technique and announced recently by researchers at the Naval Research Laboratory (NRL), the University of Dortmund, and the University of Bochum, is an important step toward realization of such quantum devices based on solid-state technology. The complete findings of the study are published in the September 28, 2007, issue of the journal Science.
An electron spin localized in a quantum dot is the quantum bit, which is the basic unit for solid-state based quantum computing and quantum information processing. The spin replaces a classical digital bit, which can take on two values, usually labeled 0 and 1. The electron spin can also take on two values. However, since it is a quantum object, it can also take all values in between. Obviously, such a quantum unit can hold much more information than a classical one and, even more importantly the use of such quantum bits makes certain computer calculations exponentially more efficient than those using a standard computer. That is why, scientists around the world are trying to find an efficient way to control and manipulate the electron spin in a quantum dot in order to enable new quantum devises using magnetic and electric fields.
Until now, the major problem with using charged quantum dots in such devices is that the electron spins in different quantum dots are never identical. The electron spin precession frequencies in an external magnetic field are different from each other due to small variations of the quantum dot shape and size. In addition, the electron spin precession frequency has a contribution of a random hyperfine field of the nuclear spins in the quantum dot volume. This makes a coherent control and manipulation of electron spins in an ensemble of quantum dots impossible and pushes researchers to work with individual spins and to develop single spin manipulation techniques, which are much more complicated than an ensemble manipulation technique.
The team of researchers at the University of Dortmund, NRL and the University of Bochum has taken a significant step toward solving this problem by suggesting a new technique that would allow coherent manipulations of an ensemble of electron spins. Last year in a Science publication (Science, vol. 313, 341 (2006)), the same research team demonstrated a method, whereby a tailored periodic illumination with a pulsed laser can drive a large fraction of electron spins (up to 30%) in an ensemble of quantum dots into a synchronized motion. In the new Science publication, the team shows that almost the whole ensemble of electron spins (90%) precesses coherently under periodic resonant excitation. It turns out that the nuclear contribution to the electron spin precession acts constructively by focusing the electron spin precession in different quantum dots to a few precession modes controlled by the laser excitation protocol, instead of acting as a random perturbation of electron spins, as it was thought previously. The modification of the laser protocol should allow scientists to reach a situation in which all electron spins have the same precession frequency, in other words to make all spins identical.
Future efforts involving the use of these identical electron spins will focus on demonstrating all coherent single q-bit operations using an ensemble of charged quantum dots. Another important use of such ensembles for quantum computing will be the demonstration of a quantum-dot gate operation. The macroscopic coherent precession of the electron spin ensemble will allow scientists to study several optical coherent phenomena, such as electromagnetically induced transparency and slow light, for example.
Naval Research Laboratory
The team of researchers at the University of Dortmund, NRL and the University of Bochum has taken a significant step toward solving this problem by suggesting a new technique that would allow coherent manipulations of an ensemble of electron spins. Last year in a Science publication (Science, vol. 313, 341 (2006)), the same research team demonstrated a method, whereby a tailored periodic illumination with a pulsed laser can drive a large fraction of electron spins (up to 30%) in an ensemble of quantum dots into a synchronized motion. In the new Science publication, the team shows that almost the whole ensemble of electron spins (90%) precesses coherently under periodic resonant excitation. It turns out that the nuclear contribution to the electron spin precession acts constructively by focusing the electron spin precession in different quantum dots to a few precession modes controlled by the laser excitation protocol, instead of acting as a random perturbation of electron spins, as it was thought previously. The modification of the laser protocol should allow scientists to reach a situation in which all electron spins have the same precession frequency, in other words to make all spins identical.
Future efforts involving the use of these identical electron spins will focus on demonstrating all coherent single q-bit operations using an ensemble of charged quantum dots. Another important use of such ensembles for quantum computing will be the demonstration of a quantum-dot gate operation. The macroscopic coherent precession of the electron spin ensemble will allow scientists to study several optical coherent phenomena, such as electromagnetically induced transparency and slow light, for example.
Naval Research Laboratory
Electron Spin Current Events and Electron Spin News RSSResearchers design new graphene-based, nano-material with magnetic properties
An international team of researchers has designed a new graphite-based, magnetic nano-material that acts as a semiconductor and could help material scientists create the next generation of electronic devices like microchips.
New Exotic Material Could Revolutionize Electronics
Move over, silicon-it may be time to give the Valley a new name. Physicists at the Department of Energy's (DOE) SLAC National Accelerator Laboratory and Stanford University have confirmed the existence of a type of material that could one day provide dramatically faster, more efficient computer chips.
Scientists Discover Magnetic Superatoms
A team of Virginia Commonwealth University scientists has discovered a 'magnetic superatom' - a stable cluster of atoms that can mimic different elements of the periodic table - that one day may be used to create molecular electronic devices for the next generation of faster computers with larger memory storage.
Multiferroics -- making a switch the electric way
Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist.
UBC researchers put a new spin on electrons
In the first demonstration of its kind, researchers at the University of British Columbia have controlled the spin of electrons using a ballistic technique--bouncing electrons through a microscopic channel of precisely constructed, two-dimensional layer of semiconductor.
Device controls electron spin at room temperature
In a breakthrough for applied physics, North Carolina State University researchers have developed a magnetic semiconductor memory device, using GaMnN thin films, which utilizes both the charge and spin of electrons at room temperature.
Capture of nanomagnetic 'fingerprints' a boost for next-generation information storage media
In the race to develop the next generation of storage and recording media, a major hurdle has been the difficulty of studying the tiny magnetic structures that will serve as their building blocks.
Quantum computing spins closer
The promise of quantum computing is that it will dramatically outshine traditional computers in tackling certain key problems: searching large databases, factoring large numbers, creating uncrackable codes and simulating the atomic structure of materials.
News Bits About Qubits: Scientists Store and Retrieve Data Inside an Atom
Another step towards quantum computing - the Holy Grail of data processing and storage - was achieved when an international team of scientists that included researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) were able to successfully store and retrieve information using the nucleus of an atom.
Zooming way in, technique offers close-ups of electrons, nuclei
Providing a glimpse into the infinitesimal, physicists have found a novel way of spying on some of the universe's tiniest building blocks.
More Electron Spin Current Events and Electron Spin News Articles
 |
What is the Electron Spin? by Gengyun Li (Author) The electron spin was discovered by S.A. Goudsmit and George Uhlenbeck in 1925. As far as we can understand, electron spin is the electron's intrinsic angular momentum. As far as we can tell, the electron is still regarded as a point like particle, with no internal structure and no physical size. How can a point particle, without any physical size, spin and have intrinsic angular momentum? The spinning of the point particle is meaningless. What matters is where the intrinsic angular momentum originates from inside the electron. There are many people who believe that an electron's mass may have an electromagnetic origin. Is there a possibility then that the electron spin also has an electromagnetic origin? The book What Is the Electron Spin? tries to answer this... |
 |
Handbook of Electron Spin Resonance by Charles P. Jr. Poole (Editor), Horacio A. Farach (Editor) Market: Physicists, chemists, biochemists, and biologists. Here's the first book to gather the vast range of experimental data in electron spin resonance (ESR) into a single volume. Concise yet comprehensive, it offers an easy-to-use collection of up-to-date experimental data, methods, and theory. The Handbook includes key contributions from leading scientists and provides over 200 tables and figures. Although specific ESR subfields are covered in numerous books and journals, the Handbook of Electron Spin Resonance is the only comprehensive reference to present extensive tabulation of data and experimental results. The Handbook also provides introductions to theoretical backgrounds, methods, and instrumentation. |
 |
Spin 2004: 16th International Spin Physics Symposium; Workshop On Polerized Electron Sources and Polarimeters by Kurt Aulenbacher (Author), Italy) Spin 200 (2004 Trieste (Author), Workshop on Polarized Electron Sources A (Author), Franco Bradamante (Editor), Andrea Bressan (Editor), Anna Martin (Editor) This comprehensive volume covers the most recent advances in the field of spin physics, including the latest research in high energy and nuclear physics and the study of nuclear spin structure. The comprehensive coverage also includes polarized proton and electron acceleration and storage, as well as polarized ion sources and targets. Many significant new results and achievements on the different topics considered at the symposium are presented in this book for the first time. |
 |
Single Electron Spin Measurements in Submicron Si MOS-FETs: Random Telegraph Signal, Single Electron Spin Resonance by Ming Xiao (Author) Presented is our measurements of a single electronic spin in the gate oxide of submicron-size silicon field effect transistors. Defects near the silicon and silicon dioxide interface have profound effects on the transistor conduction properties. For a submicron transistor, there might be only one isolated trap state that is within a proper tunneling distance regarding to both the coordinate and energy. We have studied the statistics and dynamics of individual defects extensively by random telegraph signal (RTS), the stochastic switching of the channel conductivity due to the trapping of single channel electrons by the defect. We also have, for the first time, studied the spin properties of these individual defects. By investigating the dependence of RTS statistics on a ... |
 |
Electron Spin Resonance Spectroscopy for Organic Radicals by Fabian Gerson (Author), Walter Huber (Author) Electron spin resonance spectroscopy is the method used to determine the structure and life expectancy of a number of radicals. Written by Fabian Gerson and Walter Huber, top experts in the field of electron spin resonance spectroscopy, this book offers a compact yet readily comprehensible introduction to the modern world of ESR. Thanks to its comprehensive coverage, ranging from fundamental theory right up to the treatment of all important classes of organic radicals and triplet-state molecules that can be analyzed using ESR spectroscopy, this unique book is suitable for users in both research and industry. Instead of using complex mathematical derivations, the authors present a readily understandable approach to the field by interpreting sample spectra and classifying experimental... |
|
|
Handbook of Electron Spin Resonance: Vol. 2 by Charles P. Jr. Poole (Editor), Horacio A. Farach (Editor) The continuously expanding field of electron spin resonance (ESR) has broadened our understanding of physics, chemistry, biology, medicine and related sciences over the last fifty years. In the first volume Professors Poole and Farach provided one of the first definitive reference tools for this field. These handbooks bring together wide-ranging data from diverse disciplines within ESR and integrate the data into a comprehesive and definitive resource. In this second volume of the Handbook of Electron Spin Resonance, the authors present a comprehensive source subfields of ESR not covered in the first volume. Topics covered in this volume include: * Sensitivity * Field Swept versus Frequency Swept Spectra * Resonators * Line Shapes * Electron Spin Echo Envelope Modulation *... |
 |
Electron Spin Resonance: Webster's Timeline History, 1958 - 2007 by Icon Group International (Author) Webster's bibliographic and event-based timelines are comprehensive in scope, covering virtually all topics, geographic locations and people. They do so from a linguistic point of view, and in the case of this book, the focus is on "Electron Spin Resonance," including when used in literature (e.g. all authors that might have Electron Spin Resonance in their name). As such, this book represents the largest compilation of timeline events associated with Electron Spin Resonance when it is used in proper noun form. Webster's timelines cover bibliographic citations, patented inventions, as well as non-conventional and alternative meanings which capture ambiguities in usage. These furthermore cover all parts of speech (possessive, institutional usage, geographic usage) and contexts, including... |
 |
New Applications of Electron Spin Resonance: Esr Dating, Dosimetry& Microscopy by M. Ikeya (Author) This book covers an interdisciplinary field between microwave spectroscopy of electron spin resonance (ESR) and chronology science or radiation dosimetry. The main object is to determine the elapsed time with ESR from forensic medicine to the age and radiation dose in earth and space science. This book is written primarily for earth scientists as well as for archaeologists and for physicists and chemists interested in new application of the method. This book can serve as an undergraduate and graduate school textbook on applications of ESR or electron paramagnetic resonance (EPR) to geological and archaelogical dating, radiation dosimetry and microscopic magnetic resonance imaging (MRI). Introduction to ESR (EPR) and chronology science and principle of ESR dating and dosimetry are... |
 |
Electron Spin Resonance: Analysis and Interpretation by P. Rieger (Author) Electron Spin Resonance covers the obtaining, analysing and interpreting of cw X-band ESR spectra of molecules with unpaired electron (s). The purpose of the book is to describe in mathematical terms the extraction of useful information from ESR spectra about the interaction of unpaired electrons with atoms in the molecules being studied. A reader familiar with quantum mechanics should gain a thorough understanding of the origins of the phenomena which make ESR spectra possible. The information that can be obtained from the spectra are explained in detail and in a logical step-by-step fashion. Examples of spectra of organic, inorganic and organometallic molecules, both in solution and in frozen solution are shown, analysed and interpreted and the mathematical basis of this... |
|
Electron Spin Resonance: A Review of Recent Literature to Mid-1986, Part B (Electron Spin Resonance; a Review of the Literature) by M. C. R. Symons (Author), Et Al (Author) Specialist Periodical Reports provide systematic and detailed review coverage of progress in the major areas of chemical research. Written by experts in their specialist fields the series creates a unique service for the active research chemist, supplying regular critical in-depth accounts of progress in particular areas of chemistry. For over 80 years the Royal Society of Chemistry and its predecessor, the Chemical Society, have been publishing reports charting developments in chemistry, which originally took the form of Annual Reports. However, by 1967 the whole spectrum of chemistry could no longer be contained within one volume and the series Specialist Periodical Reports was born. The Annual Reports themselves still existed but were divided into two, and subsequently three, volumes... |
| © 2009 BrightSurf.com |