Proccedings of the
Quantum Coherence and Decoherence, Santa-Barbara, Dec 15-18, 1996
Quantum coherence and nonlocality were long regarded as primary manifestations of the counterintuitive nature of quantum theory. They are now also coming to be recognized as a potentially valuable resource for information processing and communication. In contact with its environment, a quantum system can loose its ability to exhibit coherence and nonlocality. The process responsible for this transition to effect ively classical behavior is known as decoherence. While shedding new light on the origins of ``the classical'' decoherence makes difficult to take advantage of the full potential offered by the quantum in communication and, especially, in computation. A challenge for physics is therefore to understand m ore thoroughly the reasons for decoherence and to devise means to preserve it. The discovery by Peter Shor that quantum computers can factor large numbers much more efficiently that their classical counterparts has brought the whole field to the limelight. In quantum computers coherence must be preserved throughout the calculation. In these Proceedings. the fundamentals of quantum computation are reviewed by DiVincenzo. The notion of quantum operations, reversible measurement an the information theoretic notions are described by Nielsen et al. and Landauer demonstrates how quantum communication can be done without requiring energy extending the analogous classical result. The second part of these proceedings concern the quantum algorithms. Josza review and generalize the quantum factoring algorithm. Zalka demonstrate how a quantum computer can be utilized for efficiently simulating quantum mechanical systems. This part ends with Cleve et al. identifying common pattern of quantum algorithms. Quantum information is extremely fragile. Not only there is little energy between the states $|0\rangle$ and $|1\rangle$ but any superpositions are also allowed. Superpositions with the different phase s have the same energy and therefore become exceedingly fragile. This fragility has been thought to imply the demise of quantum computers. Fortunately quantum error correction codes have been discovered thus giving hope that it may be possible to build quantum computers robust against imperfections. The third part of these proceedings deals with errors and quantum error correction. Paz and Zurek analyze the effect of errors on the factoring algorithm. Knill et al. introduce error correction and demonstrate an accuracy threshold theorem. A similar theorem is also proved and analyzed by Preskill. Finally, all these beautiful theoretical constructions would be like sand castles if it would not be possible to build quantum computers. Wineland gives a review of the ion trap quantum computer. Walther surveys single atom experiments in cavities and traps. And finally Gershenfeld et al. analyze a new system to realize a quantum computer: Nuclear Magnetic Resonance. Preskill concludes the Proceedings by reviews the Pros and Cons of quantum computing. We would are grateful to the Institute for Theoretical Physics in Santa-Barbara which for making this conference possible. We would like to thank the speakers and also the participants who have made this conference so interesting.
D. DiVincenzo
E. Knill
R. Laflamme
W. Zurek
The proceedings have appeared in the Proceedings: Mathematical, Physical and Engineering Sciences (Proceeedings of the Royal Society of London Series A, Volume 454, Pages 257-486, Number 1969, 8 January 1998). Here is a list of papers for the conference (in postcript).
H. Walther: Single atom experiments in cavities and traps.
R. Landauer: Energy needed to send a bit.
David Divincenzo: Quantum Gates and Circuits.
Dave Wineland: Quantum state manipulation of trapped atomic ions.
John Preskill: Reliable Quantum Computers.
John Preskill: Quantum Computing: Pro and Con
Richard Josza: Quantum Algorithms and the Fourier Transform
M. Nielsen, C. Caves, B. Schumacher and H. Barnum: Information-theoretic approach to quantum error correction and reversible measurement.
C. Zalka: Efficient Simulation of Quantum Systems by Quantum Computers.
E. Knill, R. Laflamme and W.H. Zurek: Resilient Quantum Computation: Error Models and Thresholds.
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