Thursday 10 September 2015

Is quantum entanglement mediated by an interaction?


You can get two photons entangled, and send them off in different directions; this is what happens in EPR experiments. Is the entanglement then somehow affected if one puts a thick slab of EM shielding material between the entangled photons? Have such experiments been made?


According to EPR experiments measurements of the entangled states are at odds with SR, so based on that I'd assume the answer is "no"/"don't know", but any citations would be appreciated!



Answer



The standard test for whether two things are really entangled with one another in the spooky-action-at-a-distance sense of the EPR picture is to see whether measurements of the states of the two particles violate one of the Bell inequalities, meaning that the correlation between the states is stronger than can be explained by any local hidden variable theory. This has been done with lots of systems having significant separation between the particles-- as long ago as 1982, Alain Aspect's group did a test with time-varying detectors that were separated by 40 feet or so, and the results were something like nine standard deviations away from the LHV limit.


More recently, Chris Monroe's group at the University of Maryland has done experiments where they entangle the states of two ions in two different ion traps, and showed Bell violation by something like 3.5 standard deviations. I wrote this up on the blog a while back, and the post includes links to the relevant papers. I'm not sure whether there's a complete lack of a straight-line path between the ions, but they're in completely separate vacuum chambers (mostly stainless steel), so I think it's fairly likely to meet the requirements of the question.


No comments:

Post a Comment

Understanding Stagnation point in pitot fluid

What is stagnation point in fluid mechanics. At the open end of the pitot tube the velocity of the fluid becomes zero.But that should result...