Comments on: Nobel Prize to Haroche and Wineland http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/ Sat, 20 Apr 2013 10:44:00 +0000 hourly 1 http://wordpress.org/?v=3.4.2 By: mks http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78811 mks Tue, 23 Oct 2012 01:17:33 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78811 Sean Carroll, would you say the Copenhagen Interpretation is still the Orthodox interpretation of QM? Sean Carroll,

would you say the Copenhagen Interpretation is still the Orthodox interpretation of QM?

]]> By: Rezso http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78810 Rezso Sat, 13 Oct 2012 10:36:36 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78810 "Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you’re allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule." I'm not interpreting the squared amplitudes of a superposition as probabilities! My whole point is that in decoherence theory, there are no probabilities at level of the system+measuring device+environment wavefunction. Classical probabilities only emerge after we trace over the environment. After that, we obtain a density operator wich describes the system+measuring device. The classical probabilities are the eigenvalues of the density operator. “Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you’re allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule.”

I’m not interpreting the squared amplitudes of a superposition as probabilities!

My whole point is that in decoherence theory, there are no probabilities at level of the system+measuring device+environment wavefunction.

Classical probabilities only emerge after we trace over the environment. After that, we obtain a density operator wich describes the system+measuring device.

The classical probabilities are the eigenvalues of the density operator.

]]> By: A Nobel Prize for Very Clever Quantum Experiments | Whiskey…Tango…Foxtrot? http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78809 A Nobel Prize for Very Clever Quantum Experiments | Whiskey…Tango…Foxtrot? Fri, 12 Oct 2012 20:10:34 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78809 [...] Nobel Prize to Haroche and Wineland | Cosmic Variance | Discover Magazine [...] [...] Nobel Prize to Haroche and Wineland | Cosmic Variance | Discover Magazine [...]

]]> By: David http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78808 David Fri, 12 Oct 2012 06:49:59 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78808 33. Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you're allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule. Decoherence does not solve the measurement problem. You need an interpretation on top (CI or MWI) to do that. I think our main source of disagreement is you assume once you see a measurement outcome, it is obvious the probability distribution has collapsed. To me, all that's obvious is you're entangled with that particular outcome and you have no way of accessing the other, which nonetheless keeps existing as an unaccessible part of the system's state, thus effectively splitting into two separate realities. "This doesn't mean there are infinitely many guitar strings in parallel universes": precisely. That's why "parallel universes" is a misnomer. There is only one wave function one can split into many components which cannot interact. 33. Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you’re allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule. Decoherence does not solve the measurement problem. You need an interpretation on top (CI or MWI) to do that.
I think our main source of disagreement is you assume once you see a measurement outcome, it is obvious the probability distribution has collapsed. To me, all that’s obvious is you’re entangled with that particular outcome and you have no way of accessing the other, which nonetheless keeps existing as an unaccessible part of the system’s state, thus effectively splitting into two separate realities.
“This doesn’t mean there are infinitely many guitar strings in parallel universes”: precisely. That’s why “parallel universes” is a misnomer. There is only one wave function one can split into many components which cannot interact.

]]> By: Rezso http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78807 Rezso Thu, 11 Oct 2012 19:30:24 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78807 29. Rick "QM became stronger — as if it needed any strengthening." The Copenhagen interpretation was not able to derive the preferred basis, it was chosen by an ad hoc rule. This was an important problem of the interpretation. In decoherence theory, the preferred basis of the system+measuring device Hilbert-space is generated by the unitary dynamics of the system+measuring device+environment. So QM needed strengthening and it is stronger now. 32. David Sorry, but I completely disagree with you. "Decoherence explains how a superposed state “splits” into two classical ones, but I don’t see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate." No, decoherence theory gives you a density operator and the eigenvalues of this operator are classical probabilities. And classical probabilities collapse by definition, when you learn the outcome of a measurement. This fact has nothing to do with quantum mechanics. If I throw a classical dice, then the probabilitiy distribution is (1/6, 1/6, 1/6, 1/6, 1/6, 1/6). But when I learn that the result is 3, then the probability distribution collapses to (0, 0, 1, 0, 0, 0). In my opinion, there is nothing more to explain here. "These we call “parallel universes”, which is probably a misnomer since we’re only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI." A superposition has nothing to do with parallel universes. I can represent the motion of a classical guitar string with a Fourier-series, but this doesn't mean that there are infinitely many guitar strings in parallel universes, there is only one. 29. Rick

“QM became stronger — as if it needed any strengthening.”

The Copenhagen interpretation was not able to derive the preferred basis, it was chosen by an ad hoc rule. This was an important problem of the interpretation.

In decoherence theory, the preferred basis of the system+measuring device Hilbert-space is generated by the unitary dynamics of the system+measuring device+environment.

So QM needed strengthening and it is stronger now.

32. David

Sorry, but I completely disagree with you.

“Decoherence explains how a superposed state “splits” into two classical ones, but I don’t see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate.”

No, decoherence theory gives you a density operator and the eigenvalues of this operator are classical probabilities.

And classical probabilities collapse by definition, when you learn the outcome of a measurement. This fact has nothing to do with quantum mechanics. If I throw a classical dice, then the probabilitiy distribution is (1/6, 1/6, 1/6, 1/6, 1/6, 1/6). But when I learn that the result is 3, then the probability distribution collapses to (0, 0, 1, 0, 0, 0). In my opinion, there is nothing more to explain here.

“These we call “parallel universes”, which is probably a misnomer since we’re only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI.”

A superposition has nothing to do with parallel universes. I can represent the motion of a classical guitar string with a Fourier-series, but this doesn’t mean that there are infinitely many guitar strings in parallel universes, there is only one.

]]> By: David http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78806 David Thu, 11 Oct 2012 06:59:19 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78806 Decoherence explains how a superposed state "splits" into two classical ones, but I don't see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate. Here's the picture: there is only one wave function carrying all the information about the experimental device and the experimenter. When the measurement is performed, two "regions" of the function decohere, meaning they become unable to interact with each other, therefore seeming like two effective separate wave-functions. These we call "parallel universes", which is probably a misnomer since we're only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI. If you want to explain the classical outcome without retorting to MWI, you have to postulate the collapse of the original wave-function, that is, the fact that after decoherence the wave-function "chooses" one of its parts and discards the other. That seems to me as completely ad-hoc and unjustified, since the previous interpretation already gave the results we see! Decoherence explains how a superposed state “splits” into two classical ones, but I don’t see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate.
Here’s the picture: there is only one wave function carrying all the information about the experimental device and the experimenter. When the measurement is performed, two “regions” of the function decohere, meaning they become unable to interact with each other, therefore seeming like two effective separate wave-functions. These we call “parallel universes”, which is probably a misnomer since we’re only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI.
If you want to explain the classical outcome without retorting to MWI, you have to postulate the collapse of the original wave-function, that is, the fact that after decoherence the wave-function “chooses” one of its parts and discards the other. That seems to me as completely ad-hoc and unjustified, since the previous interpretation already gave the results we see!

]]> By: Guest Post: John Preskill on Individual Quantum Systems | Cosmic Variance | Discover Magazine http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78805 Guest Post: John Preskill on Individual Quantum Systems | Cosmic Variance | Discover Magazine Thu, 11 Oct 2012 01:12:59 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78805 [...] RSS « Nobel Prize to Haroche and Wineland [...] [...] RSS « Nobel Prize to Haroche and Wineland [...]

]]> By: Shtetl-Optimized » Blog Archive » Quantum computing in the newz http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78804 Shtetl-Optimized » Blog Archive » Quantum computing in the newz Thu, 11 Oct 2012 00:56:40 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78804 [...] (10/10).  In case anyone is interested, here’s a comment I posted over at Cosmic Variance, responding to a question about the relevance of Haroche and [...] [...] (10/10).  In case anyone is interested, here’s a comment I posted over at Cosmic Variance, responding to a question about the relevance of Haroche and [...]

]]> By: Rick http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78803 Rick Wed, 10 Oct 2012 21:09:52 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78803 "Decoherence is a physical phenomena, you can measure it in the lab, and it solves the “preferred basis problem” of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger." What Scott said. QM became stronger -- as if it needed any strengthening. "Bohr did not need to explain how the wave function collapsed because it was never, to him, a physical wave to begin with. Yeah, it just about our knowledge of world, not the world itself . . . ? “Decoherence is a physical phenomena, you can measure it in the lab, and it solves the “preferred basis problem” of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger.”

What Scott said. QM became stronger — as if it needed any strengthening.

“Bohr did not need to explain how the wave function collapsed because it was never, to him, a physical wave to begin with.

Yeah, it just about our knowledge of world, not the world itself . . . ?

]]> By: Rezso http://blogs.discovermagazine.com/cosmicvariance/2012/10/09/nobel-prize-to-haroche-and-wineland/#comment-78802 Rezso Wed, 10 Oct 2012 17:12:07 +0000 http://blogs.discovermagazine.com/cosmicvariance/?p=8902#comment-78802 "To understand it better, as my knowledge is very basic: the results by Haroche and Wineland mean that “Copenhagen interpretation” is now severely weakened in favor of MWI theory ?" NO, their work is based on decoherence theory. Decoherence is a physical phenomena, you can measure it in the lab, and it solves the "preferred basis problem" of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger. “To understand it better, as my knowledge is very basic: the results by Haroche and Wineland mean that “Copenhagen interpretation” is now severely weakened in favor of MWI theory ?”

NO, their work is based on decoherence theory. Decoherence is a physical phenomena, you can measure it in the lab, and it solves the “preferred basis problem” of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger.

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