(July 14, 2014 at 1:42 pm)Cato Wrote:(July 13, 2014 at 7:35 pm)ManMachine Wrote: EPR paradox can be used to establish an indirect 'measurement' without causing wave function collapse. These 'weak measurements' are used in experiments of this nature.
This doesn't solve your information problem. You lifted this off the last two lines of the second paragraph under the 'Implications for quantum mechanics' concluding section of the EPR paradox article in Wiki. The first sentence doesn't mean what you think it does. The Wiki author likely doesn't understand 'weak measurement' any more than you do since you simply repeated his nonsensical dumping of the concept.
Quote:EPR paradox can be used to establish an indirect 'measurement' without causing wave function collapse.The indirect measurement referenced here is the idea that you can perform a 'strong measurement' on one particle of an entangled pair to indirectly measure the value of the complimentary particle. The wave function does collapse with the measurement. I'm not sure why you stated it didn't.
Quote:These 'weak measurements' are used in experiments of this nature.'Weak measurements' are not the 'indirect measurements' discussed in the preceding sentence. Beginning your sentence with 'These weak measurements' betrays some confusion.
'Weak measurement' is an experimental technique that minimally perturbs an entangled system, as to prevent wave function collapse. The key thing to note here is that the weak measurement technique must be repeated numerous times on a sequence of intentionally created identical entangled systems to average a 'weak value'. Any particular 'weak measurement' says nothing about the system from which it was taken. The 'weak value' is arrived at by averaging the results of all the 'weak measurements'. Furthermore, 'weak value' is not a specific observable value and takes the meaning of a more narrow set of possible eigenstates.
Once a 'strong measurement' is taken of a complimentary property, the 'weak value' can then be used to attempt to quantify the uncertainty of the original property that was weakly measured. This use of 'weak measurement' is still not settled science, but is the most that can be expected right now.
Much of the problem is that people writing science articles will make outlandish claims based on their ignorance of what is meant by 'weak measurement'. They interpret 'weak measurement' to mean we can know a wave function's eigenstate without collapsing the wave function. This simply isn't true. The bullshit cascades from here.
I was a little lazy with my response.
You can protect entanglement decoherence using weak measurement and quantum measurement reversal.
abstract
"Decoherence, which causes degradation of entanglement and in some cases entanglement sudden death, is a critical issue faced in quantum information. Protecting entanglement from decoherence, therefore, is essential in practical realization of quantum computing and quantum communication protocols. In this paper, we demonstrate a novel method to protect entanglement from amplitude damping decoherence via weak measurement and quantum measurement reversal. It is shown that even entanglement sudden death can be circumvented."
(Yong-Su Kim ; Jong-Chan Lee ; Osung Kwon ; Yoon-Ho Kim: 2013)
MM
"The greatest deception men suffer is from their own opinions" - Leonardo da Vinci
"I think I use the term “radical” rather loosely, just for emphasis. If you describe yourself as “atheist,” some people will say, “Don’t you mean ‘agnostic’?” I have to reply that I really do mean atheist, I really do not believe that there is a god; in fact, I am convinced that there is not a god (a subtle difference). I see not a shred of evidence to suggest that there is one ... etc., etc. It’s easier to say that I am a radical atheist, just to signal that I really mean it, have thought about it a great deal, and that it’s an opinion I hold seriously." - Douglas Adams (and I echo the sentiment)
"I think I use the term “radical” rather loosely, just for emphasis. If you describe yourself as “atheist,” some people will say, “Don’t you mean ‘agnostic’?” I have to reply that I really do mean atheist, I really do not believe that there is a god; in fact, I am convinced that there is not a god (a subtle difference). I see not a shred of evidence to suggest that there is one ... etc., etc. It’s easier to say that I am a radical atheist, just to signal that I really mean it, have thought about it a great deal, and that it’s an opinion I hold seriously." - Douglas Adams (and I echo the sentiment)