Quantum weirdness: entanglement (Introduction)

by David Turell , Wednesday, September 02, 2015, 04:41 (3153 days ago) @ David Turell

Quantum weirdness passes an important test:-http://www.nature.com/news/quantum-spookiness-passes-toughest-test-yet-1.18255-"The most rigorous test of quantum theory ever carried out has confirmed that the ‘spooky action at a distance' that the German physicist famously hated — in which manipulating one object instantaneously seems to affect another, far away one — is an inherent part of the quantum world.-"The experiment, performed in the Netherlands, could be the final nail in the coffin for models of the atomic world that are more intuitive than standard quantum mechanics, say some physicists.-***
"In the 1960s, Irish physicist John Bell proposed a test that could discriminate between Einstein's hidden variables and the spooky interpretation of quantum mechanics1. He calculated that hidden variables can explain correlations only up to some maximum limit. If that level is exceeded, then Einstein's model must be wrong.-"The first Bell test was carried out in 19812, by Alain Aspect's team at the Institute of Optics in Palaiseau, France. Many more have been performed since, always coming down on the side of spookiness — but each of those experiments has had loopholes that meant that physicists have never been able to fully close the door on Einstein's view. Experiments that use entangled photons are prone to the ‘detection loophole': not all photons produced in the experiment are detected, and sometimes as many as 80% are lost. Experimenters therefore have to assume that the properties of the photons they capture are representative of the entire set.-"To get around the detection loophole, physicists often use particles that are easier to keep track of than photons, such as atoms. But it is tough to separate distant atoms apart without destroying their entanglement. This opens the ‘communication loophole': if the entangled atoms are too close together, then, in principle, measurements made on one could affect the other without violating the speed-of-light limit.-***-"In the latest paper3, which was submitted to the arXiv preprint repository on 24 August and has not yet been peer reviewed, a team led by Ronald Hanson of Delft University of Technology reports the first Bell experiment that closes both the detection and the communication loopholes. The team used a cunning technique called entanglement swapping to combine the benefits of using both light and matter. The researchers started with two unentangled electrons sitting in diamond crystals held in different labs on the Delft campus, 1.3 kilometres apart. Each electron was individually entangled with a photon, and both of those photons were then zipped to a third location. There, the two photons were entangled with each other — and this caused both their partner electrons to become entangled, too.-"This did not work every time. In total, the team managed to generate 245 entangled pairs of electrons over the course of nine days. The team's measurements exceeded Bell's bound, once again supporting the standard quantum view. Moreover, the experiment closed both loopholes at once: because the electrons were easy to monitor, the detection loophole was not an issue, and they were separated far enough apart to close the communication loophole, too.-“'It is a truly ingenious and beautiful experiment,” says Anton Zeilinger, a physicist at the Vienna Centre for Quantum Science and Technology."-Comment: this is explained only if one invokes a separate plane of quantum reality parallel to ours, per Kastner.