Quantum computing spins closer

November 24, 2008

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.

A quantum step in that direction, if you'll pardon the pun, has been taken by Stanford researchers who announced their success in a paper published in the journal Nature. Working in the Ginzton Laboratory, they've employed ultrafast lasers to set a new speed record for the time it takes to rotate the spin of an individual electron and confirm the spin's new position.

Why does that matter? Existing computers, from laptops to supercomputers, see data as bits of information. Each bit can be either a zero or a one. But a quantum bit can be both zero and one at the same time, a situation known as a superposition state. This allows quantum computers to act like a massively parallel computer in some circumstances, solving problems that are almost impossible for classic computers to handle.

Quantum computing can be accomplished using a property of electrons known as "spin." A single unit of quantum information is the qubit, and can be constructed from a single electron spin, which in this experiment was confined within a nano-sized semiconductor known as a quantum dot.

An electron spin may be described as up or down (a variation of the usual zero and one) and may be manipulated from one state to another. The faster these electrons can be switched, the more quickly numbers can be crunched in a quantum fashion, with its intrinsic advantages over traditional computing designs.

The qubit in the Stanford experiment was manipulated and measured about 100 times faster than with previous techniques, said one of the researchers, David Press, a graduate student in applied physics.

The experiments were conducted at a temperature of almost absolute zero, inside a strong magnetic field produced by a superconducting magnet. The researchers first hit the qubit with laser light of specific frequencies to define and measure the electron spin, all within a few nanoseconds. Then they rotated the spin with polarized light pulses in a few tens of picoseconds (a picosecond is one trillionth of a second). Finally, the spin state was read out with yet another optical pulse.

Similar experiments have been done before, but with radio-frequency pulses, which are slower than laser-light pulses. "The optics were quite tricky," Press said. The researchers had to find a single, specific photon emitted from the qubit in order confirm the spin state of the electron. That photon, however, was clouded in a sea of scattered photons from the lasers themselves.

"The big benefit is to make quantum computing faster," Press said. The experiment "pushed quantum dots up to speed with other qubit candidate systems to ultimately build a quantum computer."

Quantum computers are still years away. In the shorter term, Press said, researchers would like to build a system of tens or hundreds of qubits to simulate the operation of a larger quantum system.

The other authors of the Nature paper were Bingyang Zhang of the Ginzton Lab, and Thaddeus Ladd and Yoshihisa Yamamoto of the Ginzton Lab and the National Institute of Informatics in Tokyo.

Stanford University

---

---

	Quantum Computing: A Gentle Introduction (Scientific and Engineering Computation) by Eleanor G. Rieffel (Author), Wolfgang H. Polak (Author) The combination of two of the twentieth century's most influential and revolutionary scientific theories, information theory and quantum mechanics, gave rise to a radically new view of computing and information. Quantum information processing explores the implications of using quantum mechanics instead of classical mechanics to model information and its processing. Quantum computing is not about changing the physical substrate on which computation is done from classical to quantum but about changing the notion of computation itself, at the most basic level. The fundamental unit of computation is no longer the bit but the quantum bit or qubit. This comprehensive...
	Quantum Computing for Computer Scientists by Noson S. Yanofsky (Author), Mirco A. Mannucci (Author) The multidisciplinary field of quantum computing strives to exploit some of the uncanny aspects of quantum mechanics to expand our computational horizons. Quantum Computing for Computer Scientists takes readers on a tour of this fascinating area of cutting-edge research. Written in an accessible yet rigorous fashion, this book employs ideas and techniques familiar to every student of computer science. The reader is not expected to have any advanced mathematics or physics background. After presenting the necessary prerequisites, the material is organized to look at different aspects of quantum computing from the specific standpoint of computer science. There are chapters on computer architecture, algorithms, programming languages, theoretical computer science, cryptography, information...
	Quantum Computation and Quantum Information: 10th Anniversary Edition by Michael A. Nielsen (Author), Isaac L. Chuang (Author) One of the most cited books in physics of all time, Quantum Computation and Quantum Information remains the best textbook in this exciting field of science. This 10th anniversary edition includes an introduction from the authors setting the work in context. This comprehensive textbook describes such remarkable effects as fast quantum algorithms, quantum teleportation, quantum cryptography and quantum error-correction. Quantum mechanics and computer science are introduced before moving on to describe what a quantum computer is, how it can be used to solve problems faster than 'classical' computers and its real-world implementation. It concludes with an in-depth treatment of quantum information. Containing a wealth of figures and exercises, this well-known textbook is ideal for courses on...
	Natural Computing: DNA, Quantum Bits, and the Future of Smart Machines by Dennis E. Shasha (Author), Cathy Lazere (Author) Reports from the cutting edge, where physics and biology are changing the fundamental assumptions of computing.Computers built from DNA, bacteria, or foam. Robots that fix themselves on Mars. Bridges that report when they are aging. This is the bizarre and fascinating world of Natural Computing. Computer scientist and Scientific American’s “Puzzling Adventures” columnist Dennis Shasha here teams up with journalist Cathy Lazere to explore the outer reaches of computing. Drawing on interviews with fifteen leading scientists, the authors present an unexpected vision: the future of computing is a synthesis with nature. That vision will change not only computer science but also fields as disparate as finance, engineering, and medicine. Space engineers are at work designing machines that...
	An Introduction to Quantum Computing by Phillip Kaye (Author), Raymond Laflamme (Author), Michele Mosca (Author) This concise, accessible text provides a thorough introduction to quantum computing - an exciting emergent field at the interface of the computer, engineering, mathematical and physical sciences. Aimed at advanced undergraduate and beginning graduate students in these disciplines, the text is technically detailed and is clearly illustrated throughout with diagrams and exercises. Some prior knowledge of linear algebra is assumed, including vector spaces and inner products. However, prior familiarity with topics such as tensor products and spectral decomposition is not required, as the necessary material is reviewed in the text.
	Quantum Computer Science: An Introduction by N. David Mermin (Author) In the 1990's it was realized that quantum physics has some spectacular applications in computer science. This book is a concise introduction to quantum computation, developing the basic elements of this new branch of computational theory without assuming any background in physics. It begins with an introduction to the quantum theory from a computer-science perspective. It illustrates the quantum-computational approach with several elementary examples of quantum speed-up, before moving to the major applications: Shor's factoring algorithm, Grover's search algorithm, and quantum error correction. The book is intended primarily for computer scientists who know nothing about quantum theory, but will also be of interest to physicists who want to learn the theory of quantum computation, and...
	Quantum Computing: From Linear Algebra to Physical Realizations by Mikio Nakahara (Author), Tetsuo Ohmi (Author) Covering both theory and progressive experiments, Quantum Computing: From Linear Algebra to Physical Realizations explains how and why superposition and entanglement provide the enormous computational power in quantum computing. This self-contained, classroom-tested book is divided into two sections, with the first devoted to the theoretical aspects of quantum computing and the second focused on several candidates of a working quantum computer, evaluating them according to the DiVincenzo criteria. Topics in Part I Linear algebra Principles of quantum mechanics Qubit and the first application of quantum information processing—quantum key distribution Quantum gates Simple yet elucidating examples of quantum algorithms Quantum circuits that implement integral transforms ...
	Quantum Computing (Natural Computing Series) by Mika Hirvensalo (Author) Mika Hirvensalo maps out the new multidisciplinary research area of quantum computing. The text contains an introduction to quantum computing as well as the most important recent results on the topic. The presentation is uniform and computer science-oriented. Thus, the book differs from most of the previous ones which are mainly physics-oriented. The special style of presentation makes the theory of quantum computing accessible to a larger audience. Many examples and exercises ease the understanding. In this second edition, a new chapter on quantum information has been added and numerous corrections, amendments, and extensions have been incorporated throughout the entire text.
	Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos by Seth Lloyd (Author) Is the universe actually a giant quantum computer? According to Seth Lloyd, the answer is yes. All interactions between particles in the universe, Lloyd explains, convey not only energy but also information–in other words, particles not only collide, they compute. What is the entire universe computing, ultimately? “Its own dynamical evolution,” he says. “As the computation proceeds, reality unfolds.” Programming the Universe, a wonderfully accessible book, presents an original and compelling vision of reality, revealing our world in an entirely new light.
	A Shortcut Through Time: The Path to the Quantum Computer by George Johnson (Author) In this remarkably illustrative and thoroughly accessible look at one of the most intriguing frontiers in science and computers, award-winning New York Times writer George Johnson reveals the fascinating world of quantum computing—the holy grail of super computers where the computing power of single atoms is harnassed to create machines capable of almost unimaginable calculations in the blink of an eye. As computer chips continue to shrink in size, scientists anticipate the end of the road: A computer in which each switch is comprised of a single atom. Such a device would operate under a different set of physical laws: The laws of quantum mechanics. Johnson gently leads the curious outsider through the surprisingly simple ideas needed to understand this dream, discussing the...