Entanglement beats gravitational test


News posted to the arXiv blog of a new experimental test of Bell’s inequality and the effects of entanglement:

“Entanglement is the state in which two physically separated particles share the same quantum existence, so that a measurement on one instantaneously affects the other. Yep, that’s instantaneously. It’s what Einstein described as ‘spooky action at distance’.

For some years, physicists have been measuring this ‘spooky action at a distance’ in tests known as Bell experiments.

These tests depend crucially on the measurement ending quickly. Because if it were to drag on, the particles might be able to communicate at light speed by some currently unknown mechanism.

But because nobody has actually determined when a measurement ends, all the experiments to date are potentially open to this loophole.

Perhaps there is no spooky action at a distance after all, just long quantum measurements during which the particles communicate at the speed of light in some quite ordinary way.

[…]So Gisin and buddies set up a Bell experiment which involved sending entangled photons in each direction from the midpoint of an 18 km fibre. At the ends of the fibre were piezoelectric actuators attached to small but massive mirrors. When the photons hit, they triggered the actuators causing the mirrors to move and deflect a beam of light.

The experiment was carefully set up so that the mirrors were heavy enough to please Penrose and far enough apart that no light speed signal could travel between them in the time it took for a pair of entangled photons to ‘kick’ them.

The result? Gisin’s team confirmed that ‘spooky action at a distance’ still governs the behaviour of the entangled photons.

If you believe Penrose, this is the first experiment to ever prove ‘spooky action at a distance’. Impressive, huh?”

Read the rest here.

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