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RE: Quantum entanglement
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"Spooky action at a distance" is how Albert Einstein famously derided the concept of quantum entanglement - where objects can become linked and instantaneously influence one another regardless of distance. Now researchers suggest that this spooky action in a way might work even beyond the grave, with its effects felt after the link between objects is broken.
In experiments with quantum entanglement, which is an essential basis for quantum computing and cryptography, physicists rely on pairs of photons. Measuring one of an entangled pair immediately affects its counterpart, no matter how far apart they are theoretically. The current record distance is 144 kilometres, from La Palma to Tenerife in the Canary Islands.

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If two particles are entangled, so quantum mechanics says, any tinkering with one can cause an instantaneous change in the other, no matter how separated they are.
Einstein rejected this notion as spooky action at a distance. But what if quantum mechanics is not quite right that the change is not instantaneous, but instigated by a signal transmitted between the two entangled particles? Now an experiment performed in Switzerland has showed that, if such a signal does exist, it would have to travel at least as fast as light, and probably thousands of times faster.

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Multi-particle entanglement
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An international team of physicists has entangled three diamond nuclei for the first time. The development promotes solid-state systems to a rank of quantum systems including ions and photons that have achieved entanglement for more than two particles.

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RE: Quantum entanglement
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A team of Boston College researchers led by Asst. Prof. Vidya Madhavan (Physics) has identified an alternative explanation for the microscopic origins of the glue that binds electrons during high-temperature superconductivity, according to results published in the December 13 edition of the scientific journal Nature.
Investigating the hotly-debated issue in high temperature superconductivity research, Madhavan and her colleagues identified a signature of the quantum entity known as spin, as opposed to the vibrational energy previously identified as a potential explanation for the glue that binds electrons.


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New findings on superconductivity 'glue'
A team of BC physicists led by Asst. Prof. Vidya Madhavan has identified an alternative explanation for the origins of the 'glue' that binds electrons during high-temp superconductivity.

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An international team including scientists from the London Centre for Nanotechnology (LCN) today publishes findings in the journal Proceedings of the National Academy of Sciences (PNAS) demonstrating the dramatic effects of quantum mechanics in a simple magnet. The importance of the work lies in establishing how a conventional tool of material science neutron beams produced at particle accelerators and nuclear reactors can be used to produce images of the ghostly entangled states of the quantum world.
At the nano scale, magnetism arises from atoms behaving like little magnets called spins. In ferromagnets the kind that stick to fridge doors all of these atomic magnets point in the same direction. In antiferromagnets, the spins were thought to spontaneously align themselves opposite to the adjacent spins, leaving the material magnetically neutral overall. The new research shows that this picture is not correct because it ignores the uncertainties of quantum mechanics. In particular, at odds with everyday intuition, the quantum-mechanical physical laws which operate on the nano-scale allow a spin to simultaneously point both up and down. At the same time, two spins can be linked such that even though it is impossible to know the direction of either by itself, they will always point in opposite directions in which case they are entangled.
With their discovery, the researchers demonstrate that neutrons can detect entanglement, the key resource for quantum computing.

When we embarked on this work, I think it is fair to say that none of us were expecting to see such gigantic effects produced by quantum entanglement in the material we were studying. We were following a hunch that this material might yield something important and we had the good sense to pursue it - Professor Des McMorrow from the LCN.

The researchers next steps will be to pursue the implications for high temperature superconductors, materials carrying electrical currents with no heating and which bear remarkable similarities to the insulating antiferromagnets they have studied, and the design of quantum computers.

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The Origin Of Mass
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Presentation by Frank Wilczek



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RE: Quantum entanglement
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Title: Teleportation of massive particles without shared entanglement
Authors: A. S. Bradley, M. K. Olsen, S. A. Haine, J. J. Hope

We propose a method for quantum state transfer from one atom laser beam to another via an intermediate optical field, using Raman incoupling and outcoupling techniques. Our proposal utilises existing experimental technologies to teleport macroscopic matter waves over potentially large distances without shared entanglement.

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A team of European scientists has proved within an ESA study that the weird quantum effect called 'entanglement' remains intact over a distance of 144 kilometres.
 The experiment allows ESA to take a step closer to exploiting entanglement as a way of communicating with satellites with total security.
Quantum entanglement is one of the many non-intuitive features of quantum mechanics. If two photons of light are allowed to properly interact with one another, they can become entangled. One can even directly create pairs of entangled photons using a non-linear process called Spontaneous Parametric Down Conversion (SPDC).

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Quantum phase shifts
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The first demonstration of a fundamentally new method for measuring a particular quantum property of individual atoms will be described in a research paper to be published in the April 19 edition of the journal Nature.

"This method allows us to directly and precisely measure the phase shifts that result when ultracold atoms collide, in a way that is independent of the accuracy-limiting density of the atoms" - Kurt Gibble, an associate professor of physics and principal investigator of the Penn State research team that developed the method.

The researchers developed an innovative way to study atomic collisions in a caesium fountain clock -- the kind of atomic clock used to keep the world's standard of time. Atomic clocks use the quantum oscillations of ultra-cold atoms, which tick at regular intervals, to gauge the passage of time. The Penn State team was able to measure accurately the shift in the atom's quantum oscillations, or phase shifts, that it experiences during a collision with another atom.
These phase shifts, which cause jumps in the atom's ticks, limit the accuracy of the world's most accurate atomic clocks. Until this study, these shifts had been impossible to measure with high precision because earlier techniques relied on knowing the atom's density, which cannot be measured accurately.

"Atomic clocks detect the entire wave-function of the atom, and this gives a frequency shift that is proportional to the density of the atoms. But, in our new technique, we detect only the part of each atom's wave function that is scattered during a collision with another atom, and these atoms see a huge frequency shift that is independent of the density of the atoms" - Kurt Gibble.

The method detects s-wave shifts or jumps in time that the atoms experience during a collision.
These s-wave phase shifts are of vital importance in many areas of research in contemporary atomic physics; for example, efforts to make use of such exotic concoctions as Bose-Einstein condensates and degenerate Fermi gasses.

"The dreams for Bose-Einstein condensates include using them to make an atom laser that would be orders of magnitude more sensitive than a regular laser to enable ultra-precise navigation and measuring gravity so precisely that you perhaps could detect oil or other gravity anomalies underground. Degenerate Fermi gasses may shed light on important condensed-matter physics problems, including high-temperature superconductivity, which could have enormous technological implications including dramatically improving the efficiency and speed of electronic circuits and computers" - Kurt Gibble.

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