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This Google Talk https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc uses entanglement and quantum information theory in a c

This Google Talk https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc uses entanglement and quantum information theory in a clear and understandable way to explain 'spooky' quantum phenomena, like the quantum eraser, de-coherence, the aspect experiment, and the measurement problem. Even if you don't know any QM, just basic algebra and calculus, it's really approachable. I used to be a fan of the Many Worlds interpretation, but after seeing this, I'm now a big fan of the Quantum Information Theory explanation. Starting about 43 minutes in, he goes into the QM Information Theory explanation, but I'd recommend watching the entire prezo. Link to my original post on the subject: https://plus.google.com/110412141990454266397/posts/HC49S9ipwgn https://plus.google.com/110412141990454266397/posts/HC49S9ip...

lisper 13y ago
And the paper that the talk is based on: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf
tedsanders 13y ago
I'm having a difficult time following his explanation. Here are a few of my stumbling points. Maybe you can help me out. 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? 3) Why does the interpretation rely on the density matrix? I've always thought of the density matrix as something that gives information about our ignorance rather than the system (this is why the density matrix mixes classical probabilities in alongside quantum amplitudes/probabilities - observer uncertainty is classical). Therefore, to me, any good interpretation of quantum mechanics ought to work without density matrices. Unfortunately his paper here (http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf) doens't seem to have significantly more information than his talk. Thanks for any help you can offer.
- carlob 13y ago
  Without reading the paper or watching the video. > 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? The density matrix does not have the same properties of a joint probability distribution, so quantum entropy doesn't really have the same properties of classical entropy. [1] > 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? The log of a matrix is defined as the inverse of the matrix exponential. The matrix exponential can be defined as the usual power series, only using matrices rather than scalars. What one usually does is: diagonalize the matrix (if possible), take the log of the eigenvalues and rotate again. Obviously taking the log of a matrix is a little trickier than the exponential because if you have negative or complex-valued eigenvalues you have to be a bit more careful. [1] http://arxiv.org/abs/quant-ph/9610005 http://arxiv.org/abs/quant-ph/9610005
  - tedsanders 13y ago
    Thanks for the link - it's exactly what I needed!
  - sinesha 13y ago
    Good answers. Just a small comment: quantum entropy is a generalization of classical entropy. In particular, if A and B are classically correlated, then S(A|B) has all the properties of a classical entropy (Shannon's, in this case), for instance, it is non-negative.
    - tedsanders 13y ago
      What does classically correlated mean? Is it different than quantum correlated? (Is this analogous to the difference between pure and mixed states?)
- frozenport 13y ago
  Didn't watch but, 1. Super-correlation is entanglement. 2. Tr (ρ log_2 ρ ) = Σ_k of λ_k log2 λ_k where λ_k is the k-th eigenvalue of ρ. Sometimes the log2 is instead ln. 3. Density matrix indicates degree of entanglement. You can measure L or R polarized light but you have an entanglement of the two. Mind you that detecting a bell state without loopholes has, to my knowledge, never been done. A systems density matrix for a system can be measured statistically (Quantum tomography?).
Tenoke 13y ago
>I used to be a fan of the Many Worlds interpretation, but after seeing this, I'm now a big fan of the Quantum Information Theory explanation. I know that both MWI and QIT interpret entanglement differently but I am not sure if I understand why one precludes the other (Your g+ post didn't help me much). Can you please point out exactly where the conflict lies, as they still seem compatible to me (perhaps with minor adjustments)?
loup-vaillant 13y ago
I must say, I'm not sure what he even means by this "zero universe" business. Sure, the classical illusion is bust, but the wave function itself, as far as we know, is real, is it not? While we're at throwing quantum explanation links, here is the Quantum Physics Sequence on Lesswrong: http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ I'd say the math is even simpler there, yet the explanation go deeper. It's a long read however.
- arethuza 13y ago
  Doesn't it depend on what it means for a theoretical construct to be "real" or not? Isn't "does it work" a better question?
  - loup-vaillant 13y ago
    Don't get confused by simple words such as "real". It means what it obviously mean in everyday life. For instance, apples are real, and gravity is real. So when you drop an apple, what happens? It falls. Now what really, ultimately happens? It falls.
    - john_cage 13y ago
      Once in Hawaii, at a meeting of philosophers sitting around a table discussing reality, several days passed and Suzuki said nothing. And finally the chairman said, "You've been silent all this time. Would you say something about reality." And Suzuki didn't say anything. I think he may have looked up. Finally the man said, "Well, is this table real?" And Suzuki said, "Yes." And then the man said, "In what sense is it real?" And Suzuki said, "In every sense."
  - aufreak3 13y ago
    Recently, there was a paper talking about this aspect of quantum theory - http://xxx.lanl.gov/abs/1111.3328 http://xxx.lanl.gov/abs/1111.3328 ... well, it was "recently" and fresh in my mind, but it appears to be back in 2011 :)
- 13y ago
johnbm 13y ago
I like it too, because it's the first explanation of QM I've heard that isn't just about minuscule systems floating in a void. I did the double slit experiment in uni, and it involved a real screen and a real divider with real slits, made out of 10^n atoms. Feynman's line integrals say that particles explore all possible paths. This would seem to include possibly interacting with all those atoms that are nearby. Yet we pretended none of that mattered and could just talk about the photons. QIT seems entirely unsurprising to me. Especially the idea about measurement and two opposite interference patterns. This also isn't the first time I've heard software guys take to it. I think it's because programmers deal with much larger scale than most occupations. We do not delegate to junior aides, we construct our own robot aides, and then deploy them on a massive scale. It always surprises me when mathematicians and physicists are crappy programmers who fail at making basic complex systems work. If you can't handle complexity, how can you handle the universe?
api 13y ago
You would probably enjoy Dr. Chris Adami's Reddit AMA: http://www.reddit.com/r/science/comments/236ap1/science_ama_series_im_chris_adami_the_guy_that/ http://www.reddit.com/r/science/comments/236ap1/science_ama_... There seems to be a growing understanding that our universe is actually made of three things, not two: matter, energy, and information. Informatics is joining with thermodynamics and matter physics / chemistry as a fundamental science of "stuff."
chm 13y ago
It's important to capitalize the A in Aspect, as it refers to the name of the physicist. http://en.wikipedia.org/wiki/Alain_Aspect http://en.wikipedia.org/wiki/Alain_Aspect

lisper 13y ago

And the paper that the talk is based on: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf

tedsanders 13y ago

I'm having a difficult time following his explanation. Here are a few of my stumbling points. Maybe you can help me out. 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? 3) Why does the interpretation rely on the density matrix? I've always thought of the density matrix as something that gives information about our ignorance rather than the system (this is why the density matrix mixes classical probabilities in alongside quantum amplitudes/probabilities - observer uncertainty is classical). Therefore, to me, any good interpretation of quantum mechanics ought to work without density matrices. Unfortunately his paper here (http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf) doens't seem to have significantly more information than his talk. Thanks for any help you can offer.

carlob 13y ago
Without reading the paper or watching the video. > 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? The density matrix does not have the same properties of a joint probability distribution, so quantum entropy doesn't really have the same properties of classical entropy. [1] > 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? The log of a matrix is defined as the inverse of the matrix exponential. The matrix exponential can be defined as the usual power series, only using matrices rather than scalars. What one usually does is: diagonalize the matrix (if possible), take the log of the eigenvalues and rotate again. Obviously taking the log of a matrix is a little trickier than the exponential because if you have negative or complex-valued eigenvalues you have to be a bit more careful. [1] http://arxiv.org/abs/quant-ph/9610005 http://arxiv.org/abs/quant-ph/9610005
- tedsanders 13y ago
  Thanks for the link - it's exactly what I needed!
- sinesha 13y ago
  Good answers. Just a small comment: quantum entropy is a generalization of classical entropy. In particular, if A and B are classically correlated, then S(A|B) has all the properties of a classical entropy (Shannon's, in this case), for instance, it is non-negative.
  - tedsanders 13y ago
    What does classically correlated mean? Is it different than quantum correlated? (Is this analogous to the difference between pure and mixed states?)
frozenport 13y ago
Didn't watch but, 1. Super-correlation is entanglement. 2. Tr (ρ log_2 ρ ) = Σ_k of λ_k log2 λ_k where λ_k is the k-th eigenvalue of ρ. Sometimes the log2 is instead ln. 3. Density matrix indicates degree of entanglement. You can measure L or R polarized light but you have an entanglement of the two. Mind you that detecting a bell state without loopholes has, to my knowledge, never been done. A systems density matrix for a system can be measured statistically (Quantum tomography?).

Tenoke 13y ago

>I used to be a fan of the Many Worlds interpretation, but after seeing this, I'm now a big fan of the Quantum Information Theory explanation. I know that both MWI and QIT interpret entanglement differently but I am not sure if I understand why one precludes the other (Your g+ post didn't help me much). Can you please point out exactly where the conflict lies, as they still seem compatible to me (perhaps with minor adjustments)?

loup-vaillant 13y ago

I must say, I'm not sure what he even means by this "zero universe" business. Sure, the classical illusion is bust, but the wave function itself, as far as we know, is real, is it not? While we're at throwing quantum explanation links, here is the Quantum Physics Sequence on Lesswrong: http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ I'd say the math is even simpler there, yet the explanation go deeper. It's a long read however.

arethuza 13y ago
Doesn't it depend on what it means for a theoretical construct to be "real" or not? Isn't "does it work" a better question?
- loup-vaillant 13y ago
  Don't get confused by simple words such as "real". It means what it obviously mean in everyday life. For instance, apples are real, and gravity is real. So when you drop an apple, what happens? It falls. Now what really, ultimately happens? It falls.
  - john_cage 13y ago
    Once in Hawaii, at a meeting of philosophers sitting around a table discussing reality, several days passed and Suzuki said nothing. And finally the chairman said, "You've been silent all this time. Would you say something about reality." And Suzuki didn't say anything. I think he may have looked up. Finally the man said, "Well, is this table real?" And Suzuki said, "Yes." And then the man said, "In what sense is it real?" And Suzuki said, "In every sense."
- aufreak3 13y ago
  Recently, there was a paper talking about this aspect of quantum theory - http://xxx.lanl.gov/abs/1111.3328 http://xxx.lanl.gov/abs/1111.3328 ... well, it was "recently" and fresh in my mind, but it appears to be back in 2011 :)
13y ago

johnbm 13y ago

I like it too, because it's the first explanation of QM I've heard that isn't just about minuscule systems floating in a void. I did the double slit experiment in uni, and it involved a real screen and a real divider with real slits, made out of 10^n atoms. Feynman's line integrals say that particles explore all possible paths. This would seem to include possibly interacting with all those atoms that are nearby. Yet we pretended none of that mattered and could just talk about the photons. QIT seems entirely unsurprising to me. Especially the idea about measurement and two opposite interference patterns. This also isn't the first time I've heard software guys take to it. I think it's because programmers deal with much larger scale than most occupations. We do not delegate to junior aides, we construct our own robot aides, and then deploy them on a massive scale. It always surprises me when mathematicians and physicists are crappy programmers who fail at making basic complex systems work. If you can't handle complexity, how can you handle the universe?

api 13y ago

You would probably enjoy Dr. Chris Adami's Reddit AMA: http://www.reddit.com/r/science/comments/236ap1/science_ama_series_im_chris_adami_the_guy_that/ http://www.reddit.com/r/science/comments/236ap1/science_ama_... There seems to be a growing understanding that our universe is actually made of three things, not two: matter, energy, and information. Informatics is joining with thermodynamics and matter physics / chemistry as a fundamental science of "stuff."

chm 13y ago

It's important to capitalize the A in Aspect, as it refers to the name of the physicist. http://en.wikipedia.org/wiki/Alain_Aspect http://en.wikipedia.org/wiki/Alain_Aspect