Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The No Cloning theorem vs weak measurement

  1. Nov 3, 2014 #1
    Question: hypothesis

    Would it be possible to determine/ capture the total wave function of an ensemble using quantum tomography & weak measurement ?

    As seen in the following article.. Its been done on a photon.. My question is, could this same technique be done on an ensemble of particles ?


    http://physicsworld.com/cws/article/news/2011/jun/15/catching-sight-of-the-elusive-wavefunction



    Whether it be a mouse brain, 1TB hard drive or a full fledged computer system,

    then host" the 3d information / MRI info of said object,
    (using the wave function as a monad to generate the object)

    As seen in some quantum computing Haskell sources..




    Thereby setting up a symmetric entanglement between the two systems without causing collapse of the system being measured due to the weak measurement process ?




    In essence, constructing a Hamiltonian of the cloned system so that it may be modelled and hosted in virtual space on a quantum computer ?


    Is there any truth to this idea ?

    Could you in ANY way, sustain "macroscopic" entanglement, MICROSCOPICALLY ?


    As mentioned in such university papers as so...


    "Quantum entanglement of baby universes"

    "ABSTRACT We study quantum entanglements of baby universes which appear in non-perturbative corrections to the OSV formula for the entropy of extremal black holes in type IIA string theory compactified on the local Calabi–Yau manifold defined as a rank 2 vector bundle over an arbitrary genus G Riemann surface. This generalizes the result for G=1 in hep-th/0504221. Non-perturbative terms can be organized into a sum over contributions from baby universes, and the total wave-function is their coherent superposition in the third quantized Hilbert space. We find that half of the universes preserve one set of supercharges while the other half preserve a different set, making the total universe stable but non-BPS.
    The parent universe generates baby universes by brane/anti-brane pair creation, and baby universes are correlated by conservation of non-normalizable D-brane charges under the process.
    There are no other source of entanglement of baby universes, and all possible states are superposed with the equal weight."


    Would it then be entangled with its real world counter part residing in the "parent" universe ?



    Could this same method not be applied to nearly anything, so long as it is placed into the phase space of the "child" baby universe ?


    Now many might thinking.. Even if you could do this.. Making observations of that system would collapse its state, making the simulated system decohere...

    Not so according to this source..

    http://www.i-sis.org.uk/HNTCTWF.php



    Are there any physicists out there willing to theorize with me ?
     
  2. jcsd
  3. Nov 3, 2014 #2
    Last edited by a moderator: May 7, 2017
  4. Nov 4, 2014 #3

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    You seem to be jumping all over the place with links to all sorts of stuff.

    But a few points of clarification about QM may help.

    First you cant ever determine via observation the state of a single quantum system. Given a large ensemble of similarly prepared systems by observing all the systems you can determine the state - but not of a single system. Its not due to the uncertainty principle as one of your linked articles suggested - its due to the superposition principle and the Born rule. If you have an observation that gives yes if a system is in a certain state and no otherwise then apply it to a superposition of that state sometimes you get yes and sometimes no. To determine if a system is definitely in that state you need a large ensemble of similarly prepared systems and get yes for all of them. You cant know 100% for sure since you would need an infinite ensemble - but for a large ensemble it will for all practical purposes be true.

    Secondly the QM formalism doesn't really contain collapse - its something that's found in some interpretations - but not all - eg many worlds and the ensemble interpretation doesn't have collapse. You see many observations actually destroys what's being observed - the only observations that do not are so called filtering observations. These days such observations are considered state preparation procedures and if anything collapsed depends on how you view the state.

    The modern version of the so called wavefunction collapse problem is the issue of definite outcomes. To understand it you need to come to grips with decoherence which explains what is called apparent collapse - but not actual collapse. To understand the difference the following may help:
    http://arxiv.org/pdf/1208.0904v1.pdf

    Anyway you covered a lot of territory. So if you want to discus it further can we narrow down to a single query? At least to start with anyway - we can branch out as we proceed.

    Thanks
    Bill
     
  5. Nov 5, 2014 #4
    thanks for the replies.



    I thought all my links were relevant to each other.

    I was trying to understand entanglement of entire systems and if it were possible without causing "collapse".
    The first link dealt with capturing the wave function using tomography and weak measurement.

    the second dealt with entanglement of baby universes.. my assumption they could represent an "entire system".

    and the third, dealt with once again, weak measurement and its role in avoiding "collapse"...

    Seems pretty relevant to me but I am willing to listen to any and all views on the subject.

    to narrow it down, I guess I am wondering how you might clone a brain. or a hard drive even.. I assume both are very similar in the way they store information and tend to compute

    I am really asking because of what has occurred to myself.

    I moved in above an undercover RCMP officer who proved she had control of my computer, even though it has no wifi nor ethernet. She told me she had cloned my computer system, then proceeded to take control of it as it played music, pausing it when I asked her to prove it.. she then repeated it on cue as I asked her to again prove it.

    I am trying to determine how she did this.
     
  6. Nov 5, 2014 #5

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    The no cloning theorem is clear - you cant do that.

    But that doesn't mean you cant clone all its features relevant to the given situation so its for all practical purposes exactly the same.

    I have no idea how she did that - but you can bet your bottom dollar it wasn't by quantum trickery.

    Thanks
    Bill
     
  7. Nov 6, 2014 #6

    Nugatory

    User Avatar

    Staff: Mentor

    [QUOTE="Checkster2323, post: 4903647, member: 529501"
    I am really asking because of what has occurred to myself.

    I moved in above an undercover RCMP officer who proved she had control of my computer, even though it has no wifi nor ethernet. She told me she had cloned my computer system, then proceeded to take control of it as it played music, pausing it when I asked her to prove it.. she then repeated it on cue as I asked her to again prove it.

    I am trying to determine how she did this.[/QUOTE]

    This would be an interesting question in the computing sub forum... But QM this is not. Thread closed.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: The No Cloning theorem vs weak measurement
  1. Weak Measurements (Replies: 1)

Loading...