5 ms·

Macro quantum mechanics

13 points by jasonabelli 15y ago

deleted 15y ago
[deleted]
- zitterbewegung 15y ago
  No it doesn't. See http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mechanics http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mecha... and http://en.wikipedia.org/wiki/No-communication_theorem http://en.wikipedia.org/wiki/No-communication_theorem
  - onemoreact 15y ago
    You can't communicate arbitrary information faster than the speed of light. However, you can interpret that the propagation of a collapsing a quantum state to be faster than the speed of light. Or, as predetermined hidden variables that interact with observation in spooky ways. But, as there does not seem to be a way to test the differences between those interpretations it's not really a meaningful scientific question.
    - Anderkent 15y ago
      Or you could choose a sane interpretation that does not require amendment every time a larger object is shown 'entanglible', but still preserves locality? See macroscopic decoherence.
- deleted 15y ago
  [deleted]
_delirium 15y ago
Fwiw, this appears to be a reblog of: http://www.livescience.com/17264-quantum-entanglement-macroscopic-diamonds.html http://www.livescience.com/17264-quantum-entanglement-macros... which was previously submitted here: http://news.ycombinator.com/item?id=3302904 http://news.ycombinator.com/item?id=3302904 and also covered in the New Scientist: http://www.newscientist.com/article/dn21235-entangled-diamonds-blur-quantumclassical-divide.html http://www.newscientist.com/article/dn21235-entangled-diamon...
colanderman 15y ago
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 15y ago
  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.
- jessriedel 15y ago
  OK, I've taken a look at the actual article and it was basically what I suspected. First, they entangle the two diamond modes by beam-splitting a photon and directing the two possible photon paths towards the diamonds. (The photon scattered off the diamonds is recombined with a beam splitter and then detected, to ensure that the scattering occurred.) Then, they hit each diamond with a lazer pulse which, if the diamond's mode was excited, produced a second photon. They were able to coherently interfere the second photon, which was in a super position of originating from the first diamond and from the second diamond.
radarsat1 15y ago
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.
- jxcole 15y ago
  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 15y ago
    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.
- ww520 15y ago
  Secret communication channel? I don't know how easy to intercept quantum entanglement. I seem to remember the quantum state would collapse if it's eavesdropped.
- JoeAltmaier 15y ago
  how about sharing a private key? Share 256 quantum bits, both 'realize' the bits, now you share a private key.
- jessriedel 15y ago
  The experiments are cool for two reasons: First, they helps us learn about and control decoherence, which is the primary obstacle to building a quantum computer. Decoherence is the reason everything doesn't behave quantum mechanically all the time, and its strength generally grows exponentially with the size of the system being studied. Building a useful quantum computer will require suppressing decoherence for order 100 qubits. Second, these experiments test quantum mechanics in new physical regimes where it might break (to be superseded by new physics). Just like one will find a discrepancy with Newtonian mechanics if one starts doing experiments near the speed of light, the suspicion is that quantum mechanics might breakdown when applied to large objects. People who are unsatisfied with the interpretation of quantum mechanics are especially interested in this possibility.
jessriedel 15y ago
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 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.
sravfeyn 15y ago
Crazier the Physics becomes day by day. What happened to the Masses being inversely proportional. How did QM get into diamonds!!

13 points by jasonabelli 15y ago

deleted 15y ago

[deleted]

zitterbewegung 15y ago
No it doesn't. See http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mechanics http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mecha... and http://en.wikipedia.org/wiki/No-communication_theorem http://en.wikipedia.org/wiki/No-communication_theorem
- onemoreact 15y ago
  You can't communicate arbitrary information faster than the speed of light. However, you can interpret that the propagation of a collapsing a quantum state to be faster than the speed of light. Or, as predetermined hidden variables that interact with observation in spooky ways. But, as there does not seem to be a way to test the differences between those interpretations it's not really a meaningful scientific question.
  - Anderkent 15y ago
    Or you could choose a sane interpretation that does not require amendment every time a larger object is shown 'entanglible', but still preserves locality? See macroscopic decoherence.
deleted 15y ago
[deleted]

_delirium 15y ago

Fwiw, this appears to be a reblog of: http://www.livescience.com/17264-quantum-entanglement-macroscopic-diamonds.html http://www.livescience.com/17264-quantum-entanglement-macros... which was previously submitted here: http://news.ycombinator.com/item?id=3302904 http://news.ycombinator.com/item?id=3302904 and also covered in the New Scientist: http://www.newscientist.com/article/dn21235-entangled-diamonds-blur-quantumclassical-divide.html http://www.newscientist.com/article/dn21235-entangled-diamon...

colanderman 15y ago

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 15y ago
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.
jessriedel 15y ago
OK, I've taken a look at the actual article and it was basically what I suspected. First, they entangle the two diamond modes by beam-splitting a photon and directing the two possible photon paths towards the diamonds. (The photon scattered off the diamonds is recombined with a beam splitter and then detected, to ensure that the scattering occurred.) Then, they hit each diamond with a lazer pulse which, if the diamond's mode was excited, produced a second photon. They were able to coherently interfere the second photon, which was in a super position of originating from the first diamond and from the second diamond.

radarsat1 15y ago

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.

jxcole 15y ago
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 15y ago
  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.
ww520 15y ago
Secret communication channel? I don't know how easy to intercept quantum entanglement. I seem to remember the quantum state would collapse if it's eavesdropped.
JoeAltmaier 15y ago
how about sharing a private key? Share 256 quantum bits, both 'realize' the bits, now you share a private key.
jessriedel 15y ago
The experiments are cool for two reasons: First, they helps us learn about and control decoherence, which is the primary obstacle to building a quantum computer. Decoherence is the reason everything doesn't behave quantum mechanically all the time, and its strength generally grows exponentially with the size of the system being studied. Building a useful quantum computer will require suppressing decoherence for order 100 qubits. Second, these experiments test quantum mechanics in new physical regimes where it might break (to be superseded by new physics). Just like one will find a discrepancy with Newtonian mechanics if one starts doing experiments near the speed of light, the suspicion is that quantum mechanics might breakdown when applied to large objects. People who are unsatisfied with the interpretation of quantum mechanics are especially interested in this possibility.

jessriedel 15y ago

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 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.

sravfeyn 15y ago

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