Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Lorentz frames for Bell inequality experiment

Learn more physics!

Most recent answer: 03/20/2014
Q:
A classic two hole experiment is set up on a flatbed railroad car pulled by a train engine. The fact that the train is moving has no effect on the experiment so an observer on the railroad car gets the usual quantum weirdness results, which depend on whether or not the the holes are observed during the experiment. It should also be possible to adjust the velocity of the train, so that the leading hole is pulled out of the path of any possible leading probability wave, from the point of view of an observer standing by the tracks. My question is, has something like this experiment ever been done? If so, has there ever been the case where both observers have seen interference, assuming that the stationary observer can in fact witness the result.
- PHILIP LANKS
HEDGESVILLE
A:

I think that this is not correct: "It should also be possible to adjust the velocity of the train, so that the leading hole is pulled out of the path of any possible leading probability wave, from the point of view of an observer standing by the tracks." How would that work without violating relativity?

I think that the most dramatic evidence on the whole issue concerns the experiments involving violations of the Bell inequalities. These are the experiments that show that the quantum interference effects cannot be simulated by some complicated local variables. I'm pretty sure that variants of these have been done with both detectors in two locations in motion in opposite directions, so that from the point of view of each detector its measurement happened first. Yet the quantum correlations survive just as if the detectors were stationary with respect to each other and to the source of the detected particles. I'm just having trouble tracking down the reference.

Aha, my colleague Paul Kwiat sends this note:

Yes, non-locality experiments have been done -- I've attached three for your reference

A couple points:

a. it's hard to get detectors moving fast. In the attached article they use a 'moving beamsplitter', with a acoustic-optic modulator. In another experiment, instead they put a detector in one arm of a (polarizing) beamsplitter, and a rapidly rotating black cylinder in the other arm.

The idea is that if the photon is NOT absorbed by the cylinder, that must collapse the wave function into the arm with the detector (which is later just confirmed by the detector going off).  By adjusting the orientation of the rotating cylinder (one on each side of the non locality experiment), one can simulate various relative moving reference frames.

These include ones in which both observers think they collapsed the wave function and the somewhat stranger case where both people it was the OTHER guy that did. This latter case was predicted (in some alternative to QM) to have a disappearance of the usual high-visibility correlation fringes. Of course, the fringes were the same in all the experiments, regardless of spinning absorber. 

 

J. Phys. A: Math. Gen. 34 (2001) 7103–7109 PII: S0305-4470(01)22310-5
Experimental test of relativistic quantum state collapse with moving reference frames
H Zbinden, J Brendel,W Tittel and N Gisin

PHYSI CAL REV IEW LETTERS 25 MARCH 2002, VOLUME 88, NUMBER 12 
Quantum Correlations with Spacelike Separated Beam Splitters in Motion: Experimental Test of Multisimultaneity
André Stefanov, Hugo Zbinden, and Nicolas Gisin, Antoine Suarez

PHYSICAL REVIEW A, VOLUME 63, 022111 (2001)
Experimental test of nonlocal quantum correlation in relativistic configurations
H. Zbinden, J. Brendel, N. Gisin, and W. Tittel

Mike W.


(published on 03/20/2014)

Follow-up on this answer.