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

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SUMMARY

The experimental demonstration of uncollapsing a quantum state has been successfully achieved in a superconducting phase qubit, as reported by Nadav Katz et al. in their article published in Nature News. This process involves a weak measurement that extracts information, leading to a non-unitary transformation of the qubit state. By applying a rotation and a second partial measurement, the extracted information can be erased, effectively canceling the effects of both measurements. The fidelity of the state recovery was measured using quantum process tomography, achieving over 70% fidelity for partial-collapse strengths below 0.6.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly wavefunction collapse.
  • Familiarity with superconducting qubits and their operational principles.
  • Knowledge of quantum process tomography techniques.
  • Basic grasp of weak measurement theory in quantum systems.
NEXT STEPS
  • Research "Quantum Process Tomography" to understand the measurement techniques used in state recovery.
  • Explore "Weak Measurement Theory" to grasp the implications of extracting information without fully collapsing a state.
  • Investigate "Superconducting Qubits" and their role in quantum computing applications.
  • Examine the implications of entanglement in quantum mechanics, particularly in relation to wavefunction collapse and uncollapse.
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Quantum physicists, experimental researchers in condensed matter physics, and anyone interested in the advancements of quantum state manipulation and measurement techniques.

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

http://www.scienceagogo.com/news/20080706233709data_trunc_sys.shtml

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

http://arxiv.org/abs/0806.3547
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:
http://arxiv.org/abs/0708.0365
Uncollapsing the wavefunction

but that was theory so still needed experimental demonstration.
 
Physics news on Phys.org
marcus said:
Here's another popular article about it:
http://www.sciencedaily.com/releases/2008/08/080806140128.htm

I think it may be a first----uncollapsing a wavefunction.
Making a measurement and then unmaking it. Comment?
Does the experimental result conform with your conception of quantum mechanics?

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?)