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Quantum No-Hiding Theorem
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Title: Experimental Test of Quantum No-Hiding Theorem
Authors: Jharana Rani Samal, Arun Kumar Pati, Anil Kumar
28 Apr 2010

Linearity and unitarity are two fundamental tenets of quantum theory. Any consequence that follows from these must be respected in the quantum world. The no-cloning theorem and the no-deleting theorem are the consequences of the linearity and the unitarity. Together with the stronger no-cloning theorem they provide permanence to quantum information, thus, suggesting that in the quantum world information can neither be created nor be destroyed. In this sense quantum information is robust, but at the same time it is also fragile because any interaction with the environment may lead to loss of information. Recently, another fundamental theorem was proved, namely, the no-hiding theorem that addresses precisely the issue of information loss. It says that if any physical process leads to bleaching of quantum information from the original system, then it must reside in the rest of the universe with no information being hidden in the correlation between these two subsystems. This has applications in quantum teleportation, state randomisation, private quantum channels, thermalisation and black hole evaporation. Here, we report experimental test of the no-hiding theorem with the technique of nuclear magnetic resonance (NMR). We use the quantum state randomisation of a qubit as one example of the bleaching process and show that the missing information can be fully recovered up to local unitary transformations in the ancilla qubits. Since NMR offers a way to test fundamental predictions of quantum theory using coherent control of quantum mechanical nuclear spin states, our experiment is a step forward in this direction.

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RE: Quantum information
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Caltech Physicists Demonstrate a Four-Fold Quantum Memory

Researchers at the California Institute of Technology (Caltech) have demonstrated quantum entanglement for a quantum state stored in four spatially distinct atomic memories.
Their work, described in the November 18 issue of the journal Nature, also demonstrated a quantum interface between the atomic memories - which represent something akin to a computer "hard drive" for entanglement - and four beams of light, thereby enabling the four-fold entanglement to be distributed by photons across quantum networks. The research represents an important achievement in quantum information science by extending the coherent control of entanglement from two to multiple (four) spatially separated physical systems of matter and light.

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I can't imagine that there are very many people in the world who would bet Stephen Hawking that his physics was wrong, even fewer who would win such a bet and perhaps only one who would forget making the winning bet in the first place. That would be University of Alberta professor Don Page.
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Title: Hawking radiation as seen by an infalling observer
Authors: Eric Greenwood, Dejan Stojkovic

We investigate an important question of Hawking-like radiation as seen by an infalling observer during gravitational collapse. Using the functional Schrodinger formalism we are able to probe the time dependent regime which is out of the reach of the standard approximations like the Bogolyubov method. We calculate the occupation number of particles registered by an infalling observer and demonstrate that the distribution is not quite thermal, though it becomes thermal once the black hole is formed in his frame. We approximately fit the temperature and find that the local temperature increases as the horizon is approached. This is in agreement with what is generically expected in the absence of backreaction.

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Title: Information is Not Lost in the Evaporation of 2-dimensional Black Holes
Authors: Abhay Ashtekar, Victor Taveras, Madhavan Varadarajan

We analyse Hawking evaporation of the Callen-Giddings-Harvey-Strominger (CGHS) black holes from a quantum geometry perspective and show that information is not lost, primarily because the quantum space-time is sufficiently larger than the classical. Using suitable approximations to extract physics from quantum space-times we establish that: i)future null infinity of the quantum space-time is sufficiently long for the the past vacuum to evolve to a pure state in the future; ii) this state has a finite norm in the future Fock space; and iii) all the information comes out at future infinity; there are no remnants.

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If a black hole eats a book, what happens to the information? The latest work from a team of physicists says that in the distant future, the black hole eventually spits out the book's full contents. Even a black hole can't destroy information.
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Physicists at Penn State have provided a mechanism by which information can be recovered from black holes, those regions of space where gravity is so strong that, according to Einstein's theory of general relativity, not even light can escape. The team's findings pave the way toward ending a decades-long debate sparked by renowned physicist Steven Hawking. The team's work will be published in the 20 May 2008 issue of the journal Physical Review Letters.

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The Austrian physicist and quantum-computing pioneer Anton Zeilinger has been awarded the inaugural Issac Newton medal by the Institute of Physics. Zeilinger was honoured for "his pioneering conceptual and experimental contributions to the foundations of quantum physics, which have become the cornerstone for the rapidly-evolving field of quantum information".

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Physicists at the University of Michigan have coaxed two separate atoms to communicate with a sort of quantum intuition that Albert Einstein called "spooky."
In doing so, the researchers have made an advance toward super-fast quantum computing. The research could also be a building block for a quantum internet.
Scientists used light to establish what's called "entanglement" between two atoms, which were trapped a meter apart in separate enclosures (think of entangling like controlling the outcome of one coin flip with the outcome of a separate coin flip).
A paper on the findings appears in the Sept. 6 edition of the journal Nature.

"This linkage between remote atoms could be the fundamental piece of a radically new quantum computer architecture.  Now that the technique has been demonstrated, it should be possible to scale it up to networks of many interconnected components that will eventually be necessary for quantum information processing" - Professor Christopher Monroe, the principal investigator who did this research while at University of Michigan, but is now at the University of Maryland.

David Moehring, the lead author of the paper who did this research as a University of Michigan graduate student, says the most important feature of this experiment is the distance between the two atoms. Moehring graduated and now has a position at the Max-Planck-Institute for Quantum Optics in Germany.

"The separation of the qubits in our entangled state is the most important feature. Localised entanglement has been performed in ion trap qubits in the past, but if one desires to build a scalable quantum computer network (or a quantum internet), the creation of entanglement schemes between remotely entangled qubit memories is necessary" - Professor Christopher Monroe.

In this experiment, the researchers used two atoms to function as qubits, or quantum bits, storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process.
The atoms, which were actually ions of the rare-earth element ytterbium, are capable of emitting two different types of photon of different wavelengths. The type of photon released by each atom indicates the particular state of the atom. Because of this, each photon was entangled with its atom.
By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fibre optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Monroe says the fibre optic thread was necessary to establish entanglement of the atoms, but then the fibre could be severed and the two atoms would remain entangled, even if one were "taken to Jupiter."

Each qubit's information is like a single bit of information in a conventional computer, which is represented as a 0 or a 1. Things get weird on the quantum scale, though, and a qubit can be either a 0, a 1, or both at the same time, Monroe says. Scientists call this phenomenon "superposition." Even weirder, scientists can't directly observe superposition, because the act of measuring the qubit affects it and forces it to become either a 0 or a 1.
Entangled particles can default to the same position once measured, for example always ending in 0,0 or 1,1.

"When entangled objects are measured, they always result in some sort of correlation, like always getting two coins to come up the same, even though they may be very far apart. Einstein called this 'spooky action-at-a-distance,' and it was the basis for his nonbelief in quantum mechanics. But entanglement exists, and although very difficult to control, it is actually the basis for quantum computers" - Professor Christopher Monroe.

Scientists could set the position of one qubit and know that its entangled mate will follow suit.
Entanglement provides extra wiring between quantum circuits, Monroe says. And it allows quantum computers to perform tasks impossible with conventional computers. Quantum computers could transmit provably secure encrypted data, for example. And they could factor numbers incredibly faster than today's machines, making most current encryption technology obsolete (most encryption today is based on the inability for man or machine to factor large numbers efficiently).

The paper is titled "Entanglement of single atom quantum bits at a distance."

Source: University of Michigan

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It was always thought to be restricted to everyday types, with no magnetic sorts allowed in the door.
But the quantum dance partys guest list just got bigger.
In a paper that appeared Friday in the online edition of Physical Review Letters, University of Florida physicists report that contrary to expectations electrons in magnetic metals exhibit the same quantum tendencies as their counterparts in ordinary metals at extremely low temperatures. Rather than acting like particles that move independently of each other, they behave as waves, influencing each others paths and trajectories.
The effect is a bit like a roomful of dancers performing, arm-in-arm, a frenetic set piece.
The electrons push and pull each other around, then return to the spot where they started off, as though completing a choreographed finale.

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