

Macro quantum mechanics - jasonabelli
http://www.foxnews.com/scitech/2011/12/02/scientists-link-diamonds-in-strange-quantum-entanglement/

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jessriedel
The actual article is published in Science, which I think means there's a
moratorium (of a few months?) on releasing the full text. That's apparently
why the article's not available on the ArXiv.

The article is here:
<http://www.sciencemag.org/content/334/6060/1253.abstract>

Entangling Macroscopic Diamonds at Room Temperature

K. C. Lee, M. R. Sprague, B. J. Sussman, J. Nunn, N. K. Langford, X.-M. Jin,
T. Champion, P. Michelberger, K. F. Reim, D. England, D. Jaksch, and I. A.
Walmsley

ABSTRACT: Quantum entanglement in the motion of macroscopic solid bodies has
implications both for quantum technologies and foundational studies of the
boundary between the quantum and classical worlds. Entanglement is usually
fragile in room-temperature solids, owing to strong interactions both
internally and with the noisy environment. We generated motional entanglement
between vibrational states of two spatially separated, millimeter-sized
diamonds at room temperature. By measuring strong nonclassical correlations
between Raman-scattered photons, we showed that the quantum state of the
diamonds has positive concurrence with 98% probability. Our results show that
entanglement can persist in the classical context of moving macroscopic solids
in ambient conditions.

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_delirium
Fwiw, this appears to be a reblog of:
[http://www.livescience.com/17264-quantum-entanglement-
macros...](http://www.livescience.com/17264-quantum-entanglement-macroscopic-
diamonds.html)

which was previously submitted here:
<http://news.ycombinator.com/item?id=3302904>

and also covered in the New Scientist:
[http://www.newscientist.com/article/dn21235-entangled-
diamon...](http://www.newscientist.com/article/dn21235-entangled-diamonds-
blur-quantumclassical-divide.html)

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radarsat1
Question: Since we know that quantum entanglement does not provide for FTL
communication, then what _are_ some practical uses for it? Why does it
continue to get so much attention in research? This answer might be, "to learn
more about quantum mechanics," but my impression is that entanglement is
fairly well-understood in physics.

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jxcole
Imagine if this could be used for communication (probably not, but you never
know). That means you could have communication between two mechanical entities
at the opposite sides of the earth without worrying about pesky radio wave
things like line of sight and increased signal strength requirements over a
distance.

But a more appropriate answer is that there probably could be some sort of
application, but unless we start building stuff we won't know what we're
capable of and will be unable to engineer cool gizmos that use it.

~~~
pasbesoin
I'm just skimming comments and haven't fully absorbed the context, but even
without FTL, being able to communicate "directly" (e.g. "through" the Earth)
would significantly reduce signal travel time, compared to running around the
Earth on fiber or, longer yet, via bounced radio waves.

For one, financial market traders would have a field day with such.

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colanderman
IANAP and the article is lacking on details where I most want them, but how
does this show that the diamonds themselves are entangled, and not just the
split light beam (à la the double-slit experiment)?

~~~
jessriedel
I believe the idea is that the photons are entangled with a certain
vibrational mode in the diamonds. When you do an interference experiment with
the photons, it demonstrates that the photons are in a coherent superposition.
If the vibrational mode in the diamonds had decohered, the photons would have
automatically been decohered as well (since they were entangled with the
diamonds).

It's hard to tell for sure without being able to read the journal article,
though.

Also, it's important to note that the center-of-mass position of the diamonds
has _not_ been put in a superposition, which is what people usually mean when
they say "macroscopic superposition". This experiment only shows that a
certain vibrational mode in the diamond is superposed. (For all I know, that
vibrational mode might just involve a few atoms.) Unfortunately, this type of
link-bait is quite common in the quantum information community.

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sravfeyn
Crazier the Physics becomes day by day. What happened to the Masses being
inversely proportional. How did QM get into diamonds!!

