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An international team, including scientists from the London Centre for Nanotechnology, has detected a hidden magnetic quantum order that extends over chains of 100 atoms in a ceramic without classical magnetism. The findings, which are published today (July 26) by Science, have implications for the design of devices and materials for quantum information processing.
In quantum information processing, data is recorded and manipulated as quantum bits or qubits, generalizations of the classical 0 and 1 bits which are traditionally represented by the on and off states of conventional switches. It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems, such as code breaking, exponentially faster than classical computers.


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Quantum order
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An international team of scientists, including several at The Johns Hopkins University, has detected a hidden magnetic quantum order that extends over chains of nearly 100 atoms in a material that is otherwise magnetically disordered.
The findings, which are published online on July 26  in the journal Science, may have implications for the design of devices and materials for quantum information processing, including large-scale quantum computers capable of tackling problems exponentially faster than can conventional computers.
The teams results are important because they demonstrate that the magnetic moments (the measure of the strength of a magnetic source) of a large number of atoms can band together to form quantum states much like those of a very large molecule. Though, on the surface, these atomic compass needles seem to be disorganised and disordered.

The team was able to discern a beautiful, underlying quantum order - team member Collin Broholm, professor in the Henry A. Rowland Department of Physics and Astronomy at Johns Hopkins Krieger School of Arts and Sciences.

Quantum mechanics is normally appreciated only on the atomic scale. However, here we present evidence for a very long and very quantum mechanical magnetic molecule, Broholm said. While disordered to a classical observer, the magnetic moments of almost 100 nickel atoms arranged in a row within a solid were shown to display an underlying quantum coherence limited only by chemical and thermal impurities. The progress we made is really a demonstration of quantum coherence among a larger number of atoms in a magnet than ever before - Collin Broholm

In addition, the team has established the factors that affect the distance over which the hidden quantum order can be maintained.
That distance, as well as how it changes as a result of heating and chemical impurities in the material, may well prove to be essential in determining whether the material will have practical applications.
The team studied a ceramic material consisting of chains of nickel-centred oxygen octahedra laid end-to-end. The chains are not ordinary magnets such as people use to tack reminders onto refrigerator doors; instead, they are an exotic, quantum spin liquid in which electron spins (analogous to tiny bar magnets) point in random directions with no particular order, even at very low temperatures.
To measure the quantum order through this classically disordered liquid, scientists used neutrons to image the magnetic excitations also called flips and the distances over which they could propagate. The experiments were performed at the National Institute of Standards and Technology Centre for Neutron Research in the United States and at the ISIS particle accelerator of the Rutherford Appleton Laboratory in the United Kingdom.
The team found that, despite the apparent classical disorder, magnetic excitations could propagate over long distances up to 30 nanometers at low temperature.

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Hawking radiation
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Title: Hawking radiation of a vector field and gravitational anomalies
Authors: Keiju Murata, Umpei Miyamoto

Recently, the relation between Hawking radiation and gravitational anomalies has been used to estimate the flux of Hawking radiation for a large class of black objects. In this paper, we extend the formalism, originally proposed by Robinson and Wilczek, to the Hawking radiation of vector particles (photons). It is explicitly shown, with Hamiltonian formalism, that the theory of an electromagnetic field on d-dimensional spherical black holes reduces to one of an infinite number of massive complex scalar fields on 2-dimensional spacetime, for which the usual anomaly-cancellation method is available. It is found that the total energy emitted from the horizon for the electromagnetic field is just (d-2) times as that for a scalar field. The results support the picture that Hawking radiation can be regarded as an anomaly eliminator on horizons. Possible extensions and applications of the analysis are discussed.

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2008 Royal Society lecture
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Imperial physicist chosen to deliver 2008 Royal Society lecture
Professor Martin Plenio New Window  from Imperial's Department of Physics has been chosen to deliver the Royal Society's 2008 Clifford Paterson Lecture. Professor Plenio will speak about the opportunities emerging from his group's research into information theory and quantum physics, and he will explain how fundamental research being carried out now is paving the way for the 'quantum computers' and quantum communication devices of the future.

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RE: Quantum information
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"Nothing there," is what Case Western Reserve University physicists concluded about black holes after spending a year working on complex formulas to calculate the formation of new black holes. In nearly 13 printed pages with a host of calculations, the research may solve the information loss paradox that has perplexed physicists for the past 40 years.

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Physicist may have finally cracked the black hole information loss paradox that has befuddled physicists for the past 40 years, according to an article accepted for publication by Physical Review D, which concludes that that an outside observer can never lose objects down a black hole.
Case Western Reserve University physicistsTanmay Vachaspati, Dejan Stojkovic and Lawrence M. Krauss came to this conclusion after spending a year working on complex formulas to calculate the formation of new black holes.

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A hidden twist in the black hole information paradox
Professor Sam Braunstein, of the University of York’s Department of Computer Science, and Dr Arun Pati, of the Institute of Physics, Sainik School, Bhubaneswar, India, have established that quantum information cannot be ‘hidden’ in conventional ways, or in Braunstein’s words, "quantum information can run but it can’t hide."
This result gives a surprising new twist to one of the great mysteries about black holes.
Conventional (classical) information can vanish in two ways, either by moving to another place (e.g. across the internet), or by "hiding", such as in a coded message. The famous Vernam cipher devised in 1917 or its relative the one-time pad cryptographic code are examples of such classical information hiding: the information resides neither in the encoded message nor in the secret key pad used to decipher it - but in correlations between the two.

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What happens when you throw an elephant into a black hole?
It sounds like a bad joke, but it's a question that has been weighing heavily on Leonard Susskind's mind. Susskind, a physicist at Stanford University in California, has been trying to save that elephant for decades. He has finally found a way to do it, but the consequences shake the foundations of what we thought we knew about space and time. If his calculations are correct, the elephant must be in more than one place at the same time.

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-- Edited by Blobrana at 15:58, 2006-10-26

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Title: Almost Certain Escape from Black Holes in Final State Projection Models
Author: Seth Lloyd

Recent models of the black-hole final state suggest that quantum information can escape from a black hole by a process akin to teleportation. These models rely on a controversial process called final-state projection. This Letter discusses the self-consistency of the final-state projection hypothesis and investigates escape from black holes for arbitrary final states and for generic interactions between matter and Hawking radiation. Quantum information escapes with fidelity ≈(8/3π)2: only half a bit of quantum information is lost on average, independent of the number of bits that escape from the hole.

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Stephen Hawking’s 1974 calculation of thermal emission from a classical black hole led to his 1976 proposal that information may be lost from our universe as a pure quantum state collapses gravitationally into a black hole, which then evaporates completely into a mixed state of thermal radiation. Another possibility is that the information is not lost, but is stored in a remnant of the evaporating black hole. A third idea is that the information comes out in nonthermal correlations within the Hawking radiation, which would be expected to occur at too slow a rate, or be too spread out, to be revealed by any nonperturbative calculation.

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