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

In summary, an article has been published about the un-collapsing of a quantum state in a superconducting qubit. It has been shown that the state can be uncollapsed after a partial-collapse measurement. The fidelity of the state recovery is measured and found to be above 70%.
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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
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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?)
 

1. What is a wavefunction in the context of condensed matter physics?

A wavefunction is a mathematical description of the quantum state of a system, which includes information about the position, momentum, and other physical properties of the particles within that system. In condensed matter physics, wavefunctions are used to describe the behavior of particles at extremely low temperatures, where quantum effects become dominant.

2. Why is uncollapsing a wavefunction important in low temperature condensed matter experiments?

In low temperature condensed matter experiments, scientists are interested in studying the behavior of particles at the quantum level. When a wavefunction collapses, it gives a single outcome for the measurement of a physical property, but this limits the information that can be obtained about the system. By uncollapsing the wavefunction, scientists can gather more information about the system and better understand its behavior.

3. How is a wavefunction typically collapsed in low temperature condensed matter experiments?

A wavefunction is usually collapsed through the process of measurement, where a physical property of the system is observed and a single outcome is obtained. This can be done using various experimental techniques, such as spectroscopy or imaging, depending on the specific system being studied.

4. Can a wavefunction be uncollapsed after it has been collapsed?

In theory, it is possible to uncollapse a wavefunction after it has been collapsed. However, this process is extremely difficult and requires complex experimental techniques. In most cases, scientists are only able to partially uncollapse a wavefunction, which still provides valuable information about the system.

5. What are the potential applications of uncollapsing a wavefunction in condensed matter physics?

Uncollapsing a wavefunction can have many potential applications in condensed matter physics, including studying the behavior of quantum systems, developing new materials with unique properties, and improving our understanding of fundamental physical phenomena. It can also have practical applications in fields such as quantum computing and nanotechnology.

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