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Topic: Quantum decoherence

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	Quantum decoherence - Wikipedia, the free encyclopedia
		In the many-worlds interpretation of quantum mechanics, decoherence is responsible for the appearance of wavefunction collapse.
		Decoherence is caused by interactions with a second system which may be thought of as either "the environment" or as "a measuring device".
		Decoherence represents a major problem for the practical realization of quantum computers, since these heavily rely on undisturbed evolution of quantum coherences.
	en.wikipedia.org /wiki/Quantum_decoherence (1051 words)

	Quantum computer - Wikipedia, the free encyclopedia
		Quantum computers are different from classical computers such as DNA computers and computers based on transistors, even though these may ultimately use some kind of quantum mechanical effect (for example covalent bonds).
		In quantum mechanics, the state of a physical system (such as an electron or a photon) is described by an element of a mathematical object called a Hilbert space.
		Qubits for a quantum computer can be implemented using particles with two spin states: "up" and "down"; in fact any system, possessing an observable quantity A which is conserved under time evolution and such that A has at least two discrete and sufficiently spaced consecutive eigenvalues, is a suitable candidate for implementing a qubit.
	en.wikipedia.org /wiki/Quantum_computer (3422 words)

	[No title]
		This is the problem of decoherence and is a stumbling block for quantum computers as the potential power of quantum computers depends on the quantum parallelism brought about by the coherent state [14].
		An example of an implementation of the qubit is the 'quantum dot' which is basically a single electron trapped inside a cage of atoms [7].
		A quantum computer would, for example, allow the "Hubbard Model" (which describes the movement of electrons within a crystal) to be simulated, a task that is beyond the scope of current conventional computers.
	www-dse.doc.ic.ac.uk /~nd/surprise_97/journal/vol4/spb3 (5889 words)

	Decoherence
		Decoherence is a precondition for such classicality; the remaining criterion, approximate determinism, is not yet defined with precision and generality.
		In particular, the process of decoherence is bound to affect the states of the brain: Relevant observables of individual neurons, inc!uding chemical concentrations and electrical potentials, are macroscopic.
		Decoherence is of use within the framework of either of the two major interpretations: It can supply a definition of the branches in Everett's many-worlds interpretation, but it can also delineate the border that is so central to Bohr's point of view.
	uncletaz.com /library/scimath/decohe.html (2877 words)

	Quantum Decoherence
		Yet this is entirely consistent with the notion that modern quantum mechanics is a universal theory applicable to everything in the cosmos and even to the cosmos itself.
		The upshot of decoherence is that, regardless of whether there are any conscious observers around or not, objects which we would expect to behave essentially classically do exactly that.
		The mathematics of decoherence are incontrovertible: it is not that someone has proposed that maybe it happens, it is a necessary consequence of the existing mathematical framework.
	www.mulhauser.net /research/tutorials/decoherence (1121 words)

	An introduction to Quantum Computing
		The simulation of a quantum computer on a classical one is a computationally hard problem because the correlations among quantum bits are qualitatively different from correlations among classical bits, as first explained by John Bell.
		The answer is primarily those errors that arise as a direct result of decoherence, or the tendency of a quantum computer to decay from a given quantum state into an incoherent state as it interacts, or entangles, with the state of the environment.
		Quantum hardware, on the other hand, remains an emerging field, but the work done thus far suggests that it will only be a matter time before we have devices large enough to test Shor's and other quantum algorithms.
	www.cs.caltech.edu /~westside/quantum-intro.html (3038 words)

	NIST Ion Storage Group (Site not responding. Last check: 2007-11-07)
		When extended to many quantum bits, the parallelism of quantum superpositions allows exponential increase in speed relative to classical computers in certain algorithms, most notably an algorithm for factoring large numbers (P. Shor, ATandT) which is of interest in the field of cryptography.
		In such a computer, the quantum bits are "wired" together by virtue of their collective motion in the trap, and externally applied laser light entangles quantum bits and allows the construction of quantum logic gates.
		Quantum logic operations with trapped ions are limited by the coupling between the ion motion and the environment, resulting in quantum decoherence.
	tf.nist.gov /ion/qucomp/intro.htm (476 words)

	[No title]
		Since decoherence does not bring about a genuine collapse of the quantum state, whether or not the evolution is quantum mechanical normal depends on the initial quantum state.) As long as the evolution is quantum mechanical normal (e.g.
		Note that the degree of quantum mechanical mixing in the spin degree of freedom as measured by the Von Neumann entropy in macrostate B is positive.
		In the quantum mechanical context the probability distribution is not, in general, uniform, and the crucial task now is to prove that the quantum distribution will reproduce the predictions based on the classical uniform distribution.
	philsci-archive.pitt.edu /archive/00001940/01/Hemmo-Shenker_Quantum_Decoherence_and_the_Approach_to_Equilibrium_II.doc (8854 words)

	Research \| Quantum Mechanics (Site not responding. Last check: 2007-11-07)
		We also discuss recent progress in the understanding of the emergence of quantum probabilities and the objectification of observables, and we outline an observable-free formulation of quantum mechanics.
		We conclude that it is not only viable, but moreover compelling to regard a minimal no-collapse quantum theory as a leading candidate for a physically motivated and empirically consistent interpretation of quantum mechanics.
		This paper is intended to clarify key features of the decoherence program, including its more recent results, and to investigate their application and consequences in the context of the main interpretive approaches of quantum mechanics.
	students.washington.edu /maxl/research/qm (465 words)

	Readings from quant-ph (Site not responding. Last check: 2007-11-07)
		Decoherence in the warm wet brain is the effect of the unavoidable exchange of energy between the enormous variety of available modes of excitation.
		Indeed, in ``Quantum Computing: A View From the Enemy Camp'', cond-mat/0110326, M.I. Dyakonov makes a plausible case that, even given the possibility of error correction, the requirements on control of individual qubits are so difficult to meet by any means that no large scale quantum computer will be built in the forseeable future, if ever.
		Decoherence and Biological Feasibility'' quant-ph/0005025) respond to Tegmark's paper with a strenuous defence of the Penrose-Hameroff ``orchestrated objective reduction'' model of quantum computation in neural microtubules.
	www.poco.phy.cam.ac.uk /~mjd1014/readings.html (10956 words)

	Newsbulletin
		The world of quantum mechanics is exceedingly weird, one in which waves can act as if they were particles, particles can spontaneously pass from one side of a barrier to the other and gedanken cats can be simultaneously dead and alive.
		Decoherence, in brief, describes the constant, tenuous interactions between a system or object and its environment, a set of interactions that allows concrete behaviors to emerge from the multitude of simultaneous possibilities that quantum theory allows.
		According to quantum theory, it should take less than 20 years for Hyperion to get into a quantum state, in which it would be simultaneously in a non-classical superposition of many orientations.
	www.lanl.gov /orgs/pa/News/012899.html (1547 words)

	Quantum Philosophy: Many-Worlds and Mind Over Matter Part 3 - Philosophy
		Decoherence, which is the interference of environmental factors, seems to account for the appearance of the breakdown of the wave function.
		The quantum playing card, when balanced on an edge will fall into a superposition of both falling to the left and to the right simultaneously.
		If we recognize that thoughts can act causally as a form of decoherence, which creates the appearance of the collapse of the wave function, not only can the idea of the observer based reality be retained, but we can realize the interaction between our inner life and the world outside.
	www.bellaonline.com /articles/art31587.asp (936 words)

	Physics 219 Course Information
		Quantum Computation and Quantum Information by Michael Nielsen and Isaac Chuang, will be available in the fall of 2000.
		Therefore, since the physical world is fundamentally quantum mechanical, the foundations of information theory and computer science should be sought in quantum physics.
		A quantum computer will be much more vulnerable than a conventional digital computer to the effects of noise and of imperfections in the machine.
	theory.caltech.edu /~preskill/ph229 (1043 words)

	Quantum measurement and decoherence
		At least in principle, such a quantum superposition state could be revealed by a quantum interference experiment involving the two needle positions.
		The quantum mechanics postulates tell us that the system+meter state is a statistical mixture of exclusive outcomes (before meter read-out).
		In all models, the time scale of this evolution (decoherence time) is of the order of the meter's relaxation time (damping time) divided by a "distance" between the components of the macroscopic quantum superposition.
	www.lkb.ens.fr /recherche/qedcav/english/rydberg/nonresonant/measurement.html (551 words)

	DECOHERENCE AND QUANTUM MEASUREMENTS
		The quantum measurement problem is one of the most fascinating and challenging topics in physics both theoretically and experimentally.
		The book deals not only with the measurement processes (including imperfect measurements) but also with related interference and mesoscopic phenomena — by means of general arguments — of solvable models and of numerical simulations.
		The quantum Zeno effect and the issue of irreversibility are also discussed.
	www.worldscibooks.com /physics/3420.html (162 words)

	Physics News Update Number 297 - QUANTUM DECOHERENCE (Site not responding. Last check: 2007-11-07)
		Each of the two quantum states shifts the phase of the microwave field by a different amount--so the field also falls into a superposition of two states.
		The researchers measured this decoherence by measuring correlations between the energy levels of pairs of atoms sent through the cavity with various time delays between the atoms.
		The ENS team discovered that decoherence (as measured by the disappearance of evidence of quantum-mechanical interference between the two cavity states) proceeds at a faster rate with time, and also when the differences between the two phase shifts are increased and therefore made more distinguishable from one another.
	www.aip.org /enews/physnews/1996/split/pnu297-3.htm (216 words)

	HPS 2626 Recent Topics in Philosophy of Physics
		Seventy years later, the enormous literature in "interpretations of quantum theory" is largely given over to trying to specifying just what the physical ontology of quantum theory should be.
		This is a recent version of the idea popularly rendered as the notion that a superposition in quantum mechanics is to be associated with many worlds existing in parallel.
		Quantum mechanics tells us that, in Schroedinger's famous set up, we create a cat in a superposition of live and dead states.
	www.pitt.edu /~jdnorton/teaching/philphys (3334 words)

	theory at los alamos (Site not responding. Last check: 2007-11-07)
		Analysis of decoherence in a simple quantum computer I.Chuang, R.Laflamme and Y. Yamamototo be published in the proceeding of 5th International Symposium on the Foundations of Quantum Mechanics in the Light of New Technology - Quantum Coherence and Decoherence, 21-24 Aug, 1995, Hatoyama, Saitama, Japan.
		Quantum Logical Operations on Encoded Qubits And the figures.
		Decoherence of quantum fields: pointer states and predictability Figures J.R. Anglin and W.Zurek, to appear in Physical Review D. Precision test of decoherence Figures J.R. Anglin and W.Zurek, to appear in Physical Review D. Deconstructing decoherence J.R. Anglin, J.P. Paz and W.Zurek, to appear in Physical Review D. Cryptography
	qso.lanl.gov /qc/theory.html (316 words)

	The Net Advance of Physics (Site not responding. Last check: 2007-11-07)
		Elements of Environmental Decoherence by Erich Joos (1999/08)
		Decoherence and the Appearance of a Classical World in Quantum Theory by Erich Joos et al.
		Decoherence, einselection, and the quantum origins of the classical by Wojciech H. Zurek [Rev.
	web.mit.edu /redingtn/www/netadv/Xhistories.html (188 words)

	Quantum Mechanics
		Quantum Cybernetics: A New Perspective for Nelson's Stochastic Theory, Nonlocality, and the Klein-Gordon Equation
		Quantum Electrodynamics is free from the Einstein-Podolsky-Rosen paradox
		Quantum correlations, measurement and the origin of uncertainty
	www.vcpc.univie.ac.at /~ian/hotlist/qc/qm.shtml (1740 words)

	Quantum Theory
		Quantum Coherence in Matter: from Quarks to Solids, 42.
		CFIF Workshop on TimeAsymmetric Quantum Theory: The Theory of Resonances, 23-26 July 2003, Instituto Superior Tecnico, Lisbon, Portugal and Quantum Structures Association Meeting, 7-22 July 2004, University of Denver.
		Decoherence, irreversibility and the selection by decoherence of quantum states with definite probabilities,
	www.nu.to.infn.it /Quantum_Theory (1729 words)

	Professor Lomonaco: Quantum Computation References
		Brandt, Howard E., Qubit devices and the issue of quantum decoherence, Progress in Quantum Electronics, Vol.
		Deutsch, David, Quantum theory, the Church-Turing principle and the universal quantum computer, Proc.
		Lomonaco, Samuel J., A Quick Glance at Quantum Cryptography, Cryptologia, Vol.
	www.cs.umbc.edu /~lomonaco/qcomp/Qcomp.html (277 words)

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