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Uncollapsing a wavefunction (demo in low temp cond matter lab)

  1. Aug 11, 2008 #1


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    Uncollapse of a partial-collapsed quantum state has been accomplished in the laboratory. Here is a popular article


    An article on this by Nadav Katz et al has just appeared in Nature News. I believe this is the preprint of the article:

    Uncollapsing of a quantum state in a superconducting phase qubit
    Nadav Katz, Matthew Neeley, M. Ansmann, Radoslaw C. Bialczak, M. Hofheinz, Erik Lucero, A. O'Connell, H. Wang, A. N. Cleland, John M. Martinis, Alexander N. Korotkov
    4 pages, 4 figures
    (Submitted on 22 Jun 2008)

    "We demonstrate in a superconducting qubit the conditional recovery ('uncollapsing') of a quantum state after a partial-collapse measurement. A weak measurement extracts information and results in a non-unitary transformation of the qubit state. However, by adding a rotation and a second partial measurement with the same strength, we erase the extracted information, effectively canceling the effect of both measurements. The fidelity of the state recovery is measured using quantum process tomography and found to be above 70% for partial-collapse strength less than 0.6."

    There were were theory papers 2007 and earlier about the theoretical possibility, like this one by Jordan and Korotkov:
    Uncollapsing the wavefunction

    but that was theory so still needed experimental demonstration.
  2. jcsd
  3. Aug 17, 2008 #2


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  4. Aug 18, 2008 #3
    Thanks for these articles - very interesting.
    Uncollapsing a wave function? The obvious question here is what
    would happen in the case of an entangled particle? i.e. would the collapse
    and uncollapse be the same for the entangled particle light years away (it should be
    because they are inseparable in the QM equation)?

    If so, could we detect that the entangled partner was decollapsed too?
    (would be at FLT?)
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