Collapse of Quantum Wavefunction Captured In Slow Motion 242
ananyo writes "It is the most fundamental, and yet also the strangest postulate of the theory of quantum mechanics: the idea that a quantum system will catastrophically collapse from a blend of several possible quantum states to just one the moment it is measured by an experimentalist. Researchers have now been able to capture that collapse through the use of weak measurements — indirect probes of quantum systems that tweak a wavefunction slightly while providing partial information about its state, avoiding a sudden collapse. Atomic and solid-state physicist Kater Murch of the University of California, Berkeley, and his colleagues performed a series of weak measurements on a superconducting circuit that was in a superposition — a combination of two quantum states. They did this by monitoring microwaves that had passed through a box containing the circuit, based on the fact that the circuit's electrical oscillations alter the state of the microwaves as they pass through the box. Over a couple of microseconds, those weak measurements captured snapshots of the state of the circuit as it gradually changed from a superposition to just one of the states within that superposition — as if charting the collapse of a quantum wavefunction in slow motion."
No video in the link (Score:4, Informative)
So don't bother unless you want to read a dry paper.
Re:OT: Question about waveforms (Score:5, Informative)
Yes. You have this effect in double slit experiment, there are places where waves cancel out and you have dark place. The problem is that it's almost impossible to generate an inverse waveform from source other than the one which generated your photon. Typically it's done by splitting one waveform.
Re:Illusion? (Score:5, Informative)
Not necessarily. Wavefunction collapse is a part of some interpretations of quantum mechanics, such as the venerable Copenhagen interpretation [wikipedia.org], but many other popular interpretations do not include it. A prominent example of the latter is the many worlds [wikipedia.org] universal wavefunction [wikipedia.org] interpretation.
Interpretations of quantum mechanics are usually mathematically equivalent, which means that they make exactly the same physical predictions. So an experiment that would be a measurement of wavefunction collapse according to the Copenhagen interpretation would be a measurement of observer entanglement or similar in the many worlds interpretation, and something else in other interpretations. It's a bit like one theory saying that A=4/2 and another saying A=1*2. They agree on every prediction (A=2), and only differ in how they are formulated, and the intuition they give people.
Popular science reporting is usually very Copenhagen-heavy, but physicists are more mixed [wikipedia.org], and a large fraction of them would disagree that this experiment has measured wavefunction collapse (i.e. they will think it measured something else interesting).
Re:No video in the link (Score:5, Informative)
http://www.youtube.com/watch?v=-fSqFWcb4rE [youtube.com]
They have a video camera that takes frames faster than light can travel, so they have the technology. Problem is it requires the subject to be ungodly bright.
No. No they don't. They have a "camera" with a very fast shutter speed. Then they take millions of pictures of different laser pulses and stitch them together to create an animation that mimics a single laser pulse.
I know that the comments on youtube are pretty poor and that most people rarely read articles but this is a really cool video and if you can't be bothered to understand what you're looking at then I feel sorry for you.
Re:Information (Score:4, Informative)
Actually, many worlds violates CPT symmetry [wikipedia.org] - worldlines divide only forward in time, not backwards. CPT symmetry requires that there be no physical bias to the direction of time. CPT symmetry is plainly untrue anyway, as we have entropy. Trying to use it as an argument against Copenhagen is disingenuous at best.
MW shows every sign of being equally wrong with every other interpretation of QM at the moment. The truth is that for many people, it represents a convenient belief. Most of its advocates lack understanding of the effective distinctions between interpretations in any case, which leads to sites and arguments like this. This is particularly bad in followers of Dawkins who argue that MW solves the fine-tuning problem, where half of the problem arises from balance in mathematical entities that QM has no plausible "ratchet" for.