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Topic: Decoherence

In the News (Mon 21 Apr 14)

  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 be thought of as either "the environment" or as "a measuring device".
Decoherence also takes place in digital computation when a special device called an arbiter leaves a metastable state (a highly indeterminate quantum state) into a stable (classical state).
en.wikipedia.org /wiki/Decoherence   (1159 words)

 The Role of Decoherence in Quantum Mechanics
Decoherence is relevant (or is claimed to be relevant) to a variety of questions ranging from the measurement problem to the arrow of time, and in particular to the question of whether and how the ‘classical world’ may emerge from quantum mechanics.
Section 3 analyses the claim that decoherence solves the measurement problem, as well as the broadening of the problem through the inclusion of environmental interactions, the idea of emergence of classicality, and the motivation for discussing decoherence together with approaches to the foundations of quantum mechanics.
Decoherence in the sense of this abstract formalism is defined simply by the condition that (quantum) probabilities for wave components at a later time may be calculated from those for wave components at an earlier time and the (quantum) conditional probabilities, according to the standard classical formula, i.e., as if the wave had collapsed.
plato.stanford.edu /entries/qm-decoherence   (8918 words)

 Quantum decoherence -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-11-06)
Consequently, decoherence is an important part of the modern version of the Copenhagen interpretation, based on (Click link for more info and facts about Consistent Histories) Consistent Histories.
However, decoherence does not give a complete solution of the (Click link for more info and facts about measurement problem) measurement problem, since all components of the wave function still exist in a global superposition.
Decoherence represents a major problem for the practical realization of (Click link for more info and facts about quantum computers) quantum computers, since these heavily rely on undisturbed evolution of quantum coherences.
www.absoluteastronomy.com /encyclopedia/q/qu/quantum_decoherence.htm   (873 words)

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
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 basic principle which explains the fact of interactive decoherence is that, under ordinary circumstances for a macroscopic object coupled to an environment -- either external or internal -- wavefunctions for macroscopically distinct states very rapidly become orthogonal.
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)

 Quantum decoherence   (Site not responding. Last check: 2007-11-06)
Quantum decoherence is the general term for the of irreversible quantum entanglement.
Decoherence represents an extremely fast process for objects since these are interacting with many objects in their natural environment.
Decoherence represents a major problem for the realization of quantum computers since these heavily rely on undisturbed of quantum coherences.
www.freeglossary.com /Decoherence   (545 words)

Decoherence is a phenomenon that plays a role in many of the events in Schild's Ladder.
Beyond the novel, understanding decoherence is essential to understanding how classical physics emerges from quantum mechanics.
The basic idea is this: a quantum system, A, in isolation, behaves in a characteristically quantum-mechanical fashion, exhibiting interference effects that reflect the phase difference between the various components of its state vector.
gregegan.customer.netspace.net.au /SCHILD/Decoherence/Decoherence.html   (337 words)

 Decoherence   (Site not responding. Last check: 2007-11-06)
On the End of a Quantum Mechanical Romance Role of Decoherence in QM measurement
Decoherence caught in the act After the measurement of an atom's state is probed by a second atom...
It provides all important operations and the simulation of decoherence effects.
www.serebella.com /encyclopedia/article-Decoherence.html   (100 words)

 Decoherence Is Our Ticket Out Of The Quantum World
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.
Decoherence provides a menu of allowed states; it's a selection process that disallows flagrantly quantum states of macroscopic objects," Zurek said.
But, thanks to decoherence, Hyperion's major axis is not simultaneously pointed toward and away from Saturn, awaiting a measurement to define its orientation.
www.sciencedaily.com /releases/1999/02/990202072053.htm   (1056 words)

 Readings from quant-ph   (Site not responding. Last check: 2007-11-06)
Decoherence in the warm wet brain is the effect of the unavoidable exchange of energy between the enormous variety of available modes of excitation.
One sense is in the context of the many-worlds idea, and supposes that decoherence is sufficient to identify a splitting of the universal quantum state into observed quasi-classical parts.
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)

 [No title]
Although the role of decoherence in the emergence of classicality has been pointed out by many authors in the last years, we shall move away from the mainstream position with respect to the explanation of decoherence.
Self-induced Decoherence In the original formulation of the algebraic formalism of quantum mechanics, the algebra of observables was a C*-algebra which does not admit unbounded operators.
In the context of the self-induced approach, decoherence is not produced by the interaction between the system of interest and its environment, but results from the own dynamics of the whole quantum system governed by a Hamiltonian with continuous spectrum.
philsci-archive.pitt.edu /archive/00001883/01/Self-Induced_Decoherence_&_Classical_Limit-1.doc   (3246 words)

 Decoherence and the Many-Worlds Interpretation   (Site not responding. Last check: 2007-11-06)
The mere combination of decoherence with the many-worlds idea is like a random walk in which not only is the step size unspecified, but so are the dimensions of the state space and the directions of the co-ordinate axes.
As far as decoherence is concerned, my claim is simply that a choice of how we carve the world into ``observer'', ``environment'', and ``the observed'' also has to be made; that variations in this choice causes the details of the mathematics to vary; and that therefore many-worlds + decoherence is not a fundamental theory.
Decoherence superselects the same sets of eigenvalues every time for similar experiments no matter what the details of the heat sinks or size of the environment.
www.poco.phy.cam.ac.uk /~mjd1014/squark.html   (3879 words)

 Visualizing the Decoherence Effect
This is not a proper paper, but rather a visual demonstration of my understanding of the decoherence effect.
Now, prepare the system such that the first particle is in the superposition of coherent states as in figure 6, the second particle is in its ground state, and the particles interact.
The result is decoherence and it is shown in figure 12.
www.geocities.com /scjphysicist/decoh.html   (1258 words)

 Decoherence caught in the act   (Site not responding. Last check: 2007-11-06)
Moreover, the decoherence time is shorter, for equal field intensities, when the phase difference, and hence the distance in the phase space, between the field components is increased.
This is an essential feature of decoherence, a non-trivial relaxation mechanism since its time scale depends upon the initial quantum superposition.
Decoherence is very clearly a deadly threat on quantum computers.
www.lkb.ens.fr /recherche/qedcav/english/rydberg/nonresonant/decoherence.html   (613 words)

 Decoherence Control and Quantum Computing   (Site not responding. Last check: 2007-11-06)
This method of using nuclei to store quantum information is in principle scalable to systems containing many quantum bits, but the real significance of our work lies in the demonstration of experimental and theoretical techniques for precise control and modeling of complex quantum computers.
Decoherence can be tackled with encoding methods such as quantum error correction and avoidance (decoherence-free subspaces), or suppressed using decoupling pulses ("bang-bang").
The decoherence time of this system was shown to be quite long recently, and with the application of ultra-fast control pulses, one million quantum-gate operations that required for the quantum error correction might become possible in the future.
www.umich.edu /~mctp/events/decoh2002/participants.html   (1476 words)

 Stanford Encyclopedia article   (Site not responding. Last check: 2007-11-06)
He estimates the decoherence time of tubulin superpositions due to interactions in the brain to be less than 10-12 sec.
(2002) have shown that a revised version of Tegmark's model provides decoherence times up to 10 to 100 μ sec, and it has been argued that this can be extended up to the neurophysiologically relevant range of 10 to 100 msec under particular assumptions of the scenario by Penrose and Hameroff.
However, decoherence is just a tiny piece in the debate about the overall picture proposed by Penrose and Hameroff.
www.quantumconsciousness.org /StanfordEncyclopediaarticle.htm   (8846 words)

 Physics News Update
They can, for instance, send a gentle C-70 beam toward a grating where, behaving as if they were waves analogous to light waves, the molecules scatter in such a way as to register in detectors farther downstream in a characteristic interference pattern (see Update 579).
Decoherence, a hot topic in physics, is the process by which quantum objects (in this case C-70 molecules, acting as waves) lose their wavelike integrity by interacting with the surrounding environment.
Decoherence is what stands between the classical (bowling ball) world and the quantum (wave interference) world, and understanding how it arises will be valuable if we are every going to exploit quantum weirdness to perform future feats of quantum computation or convey secure pieces of quantum information.
www.aip.org /enews/physnews/2004/split/674-1.html   (331 words)

 Decoherence-Free Subspace   (Site not responding. Last check: 2007-11-06)
Dicke's quantum optics work on superradiance of atoms coupled to a radiation field, where it arose in the consideration of systems confined to a region whose linear dimensions are small compared to the shortest wavelength of the field.
Recall that in our simple decoherence model in section 4.7.3 we made the assumption that particles scattering off the heavy particle subjected to the decoherence superoperator all had low energy.
The decoherence free states are those, and only those states which are simultaneous degenerate eigenvectors, i.e., eigenvectors with the same energy, of all system S operators appearing in
beige.ucs.indiana.edu /B679/node118.html   (483 words)

 On the End of a Quantum Mechanical Romance
The phenomenon of interactive decoherence suggests that relevant kinds of higher level structures cannot exist in coherent quantum states, and it guarantees that even lower level structure can exist in coherent quantum states only so long as their interaction with their environment is kept to an absolute minimum.
The problem, of course, is that such an interpretation, appealing only to the theoretical constructs which have emerged from decoherence theory to date, on the face of it requires either an ignorance interpretation or an 'ad hoc' addition (pace Josephson) of the power of decoherence to 'actualise' eigenstates.
Indeed, the other outstanding problem in decoherence theory today, apart from interpreting probabilities, is the closely related problem of accounting for the uniqueness of the quasi-classical domain which arises from the processes of decoherence.
psyche.cs.monash.edu.au /volume2-1/psyche-95-2-19-decoherence-1-mulhauser.html   (6053 words)

 ePrintsUQ - Lorentz Invariant Intrinsic Decoherence
Quantum decoherence can arise due to classical fluctuations in the parameters which define the dynamics of the system.
In this case decoherence, and complementary noise, is manifest when data from repeated measurement trials are combined.
Recently a number of authors have suggested that fluctuations in the space-time metric arising from quantum gravity effects would correspond to a source of intrinsic noise, which would necessarily be accompanied by intrinsic decoherence.
eprint.uq.edu.au /archive/00000719   (165 words)

 PhilSci Archive - Self-Induced Selection: A New Approach to Quantum Decoherence
According to Zurek, decoherence is a process resulting from the interaction between a quantum system and its environment; this process singles out a preferred set of states, usually called “pointer basis”, that determines which observables will receive definite values.
This means that decoherence leads to a sort of selection which precludes all except a small subset of the states in the Hilbert space of the system from behaving in a classical manner: environment-induced-superselection (einselection) is a consequence of the process of decoherence.
The aim of this paper is to present a new approach to decoherence, different from the mainstream approach of Zurek and his collaborators.
philsci-archive.pitt.edu /archive/00000801   (193 words)

 conference Mechanisms of Decoherence   (Site not responding. Last check: 2007-11-06)
In the last decade it has become urgent to understand how quantum correlations are destroyed by various "decoherence" mechanisms.
In condensed matter physics research focuses on mesoscopic and macroscopic quantum phenomena in superconductors, metals, and magnets, as well as on "quantum computers".
In quantum gravity and cosmology decoherence may be crucial to the physics of quantum fl holes and of fluctuations in the early universe.
www1.phys.uu.nl /spinoza/decoherence/conference.htm   (91 words)

 C-70 molecules show decoherence (February 2004) - News - nanotechweb.org
Physicists in Austria have observed decoherence - the transition from quantum to classical behaviour - in carbon-70 molecules.
However, the molecules gradually become classical at higher temperatures, and the interference pattern - which is the classic sign of quantum behaviour - becomes weaker.
Since these photons could, in principle, be detected to reveal which slit the molecule has passed through, the wave-like quantum behaviour of the molecules disappears.
www.nanotechweb.org /articles/news/3/2/10/1   (375 words)

 Decoherence of matter waves by thermal emission of radiation : Nature
Decoherence of matter waves by thermal emission of radiation
One important cause of decoherence is the interaction of a quantum system with its environment, which 'entangles' the two and distributes the quantum coherence over so many degrees of freedom as to render it unobservable.
Decoherence by emission of thermal radiation is a general mechanism that should be relevant to all macroscopic bodies.
www.nature.com /doifinder/10.1038/nature02276   (256 words)

 The Everett Interpretation
If one of the systems is an observer and the interaction an observation then the effect of the observation is to split the observer into a number of copies, each copy observing just one of the possible results of a measurement and unaware of the other results and all its observer- copies.
Decoherence refers to the loss of coherency or absence of interference effects between the elements of the superposition.
The decoherence approach is useful in considering the effect of the environment on a system.
www.geocities.com /capecanaveral/hangar/6929/manyworld.html   (15592 words)

The reason is that the stresses in such precessing gyroscopes transiently induce in them a decoherence from the Machian background that makes them release their former momentum-energy, letting them evolve as Shadow matter with close to zero weight and inertia.
Optical cavities tuned to the proper resonance, reinforced by the natural superradiant modes of water and their chaotic transitions at the superparaelectric point may be all that is needed to decohere some macroscopic body from the Machian background.
Similarly to the superparamagnetic point, which results in the strong transitions of the Colossal Magnetoresistive effect in grains of the critical size near their critical temperature, the mesoscopic transitions of water are amplified in droplets of the critical size, at unstable points where two molecular liquid crystal phases coexist, near 3.95°C.
www.mypage.bluewin.ch /Bizarre/Decoh.htm   (4707 words)

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