"Experimental nonlocal and surreal Bohmian trajectories"

[StevieTNZ]

Thought people would be interested in this recently published paper:
http://advances.sciencemag.org/content/2/2/e1501466
It came up on my Facebook feed because I am friends with one of the authors.

Weak measurement allows one to empirically determine a set of average trajectories for an ensemble of quantum particles. However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle. Moreover, the theory describing these trajectories, called Bohmian mechanics, predicts trajectories that were at first deemed “surreal” when the second particle is used to probe the position of the first particle. We entangle two photons and determine a set of Bohmian trajectories for one of them using weak measurements and postselection. We show that the trajectories seem surreal only if one ignores their manifest nonlocality.

Picked up by New Scientist: https://www.newscientist.com/articl...rdness-may-hide-an-orderly-reality-after-all/

I'm a bit suspicious, due to the use of weak measurements. Thoughts on this experiment? (The full text is available for free, from the link above.)

 

[bhobba]

I'm a bit suspicious, due to the use of weak measurements. Thoughts on this experiment? (The full text is available for free, from the link above.)

The wording of your quote tells it all. Its based on a misunderstanding of the QM formalism confusing it with interpretations. It's not exactly an uncommon thing - but its wrong. I even did that before posting a lot here and I had read quite a few books at graduate level on QM - its an easy trap to fall into. The university up the road from where I live, Griffith University, unfortunately occasionally produce papers like that,and I know they have some very good quantum people. It should have been picked up by the referees. It also needs to be said there have been quite a few papers like that discussed here.

Thanks
Bill

 

[Demystifier]

Thoughts on this experiment?

The experiment confirms that QM is correct, it does not resolve the interpretation issues of QM, yet it demonstrates that Bohmian trajectories are not less measurable than the wave function.

 

[stevendaryl]

The wording of your quote tells it all. Its based on a misunderstanding of the QM formalism confusing it with interpretations.

Wait a minute...you're saying that you know that the paper is incorrect based on the quote in the original post?

 

[bhobba]

Wait a minute...you're saying that you know that the paper is incorrect based on the quote in the original post?

No - I am saying the author was careless in his wording and the claim as written can't be true because its purely interpretational. Likely ignoring that it has some element of 'truth'. To be specific - 'However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle.' is not true in the QM formalism - in the formalism there is no properties apart from observation.

We have had a number of papers discussed here that are like that. What they are trying to say is often interesting, but what they read into it leaves a bit to be desired.

Thanks
Bill

 

[stevendaryl]

No - I am saying the author was careless in his wording and the claim as written can't be true because its purely interpretational. Likely ignoring that it has some element of 'truth'. To be specific - 'However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle.' is not true in the QM formalism - in the formalism there is no properties apart from observation.

I think he's just saying that there is some notion of "trajectory" that can be associated with a quantum particle--and there certainly can be: Bohmian mechanics does (I don't understand the relationship between Bohmian trajectories and weak measurements). Of course, the claim that a particle actually moves on such a trajectory is interpretational, but you can talk about the trajectories as mathematical objects without assuming an interpretation.

 

[StevieTNZ]

From the Physorg.com article on the paper: http://phys.org/news/2016-02-quantum-surrealism.html

Steinberg points out that both the standard interpretation of quantum mechanics and the De Broglie-Bohm interpretation are consistent with experimental evidence, and are mathematically equivalent. But it is helpful in some circumstances to visualize real trajectories, rather than wave function collapses, he says.

 

[bohm2]

I was looking through this experiment but I don't understand what issue has been resolved. Obviously non-locality is a necessary feature of any realistic interpretation of QM, like BM. So, I don't understand what 25-year old debate has been resolved?

By studying how photons travel through a double slit, physicists in Canada have now shown that some photons follow "surreal trajectories" that appear to defy the laws of physics. Upon closer inspection, however, the experiment reveals that the behaviour of these rogue photons can be explained using the principle of quantum entanglement. The work has resolved a 25-year-old debate based on an alternative interpretation of quantum mechanics.

Surreal behaviour spotted in photon experiment
http://physicsworld.com/cws/article/news/2016/feb/26/surreal-behaviour-spotted-in-photon-experiment

Experimental nonlocal and surreal Bohmian trajectories
http://advances.sciencemag.org/content/2/2/e1501466.full-text.pdf+html

 

[Demystifier]

Don't read what journalists say about science. Their job is to make science more interesting to lay people than it really is. Read what scientists say, in their original scientific papers.