Dubbed by Albert Einstein as “spooky action at a distance,” the phenomenon of quantum entanglement occurs when two particles are so deeply linked that even if they are billions of light-years apart, actions impelled on one particle have an effect on the other. It's a phenomenon similar to the love bond which can develop between human beings – a different kind of powerful force which has sometimes been called spooky too.
In quantum entanglement, if one particle were spun in a clockwise direction, for instance, the other would spin counterclockwise.
"Things get really interesting when two electrons become entangled," Ronald Hanson from the University of Delft in the Netherlands said in a statement about the phenomenon.
"They are perfectly correlated, when you observe one, the other one will always be opposite. That effect is instantaneous, even if the other electron is in a rocket at the other end of the galaxy."
Initially posited by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935, quantum entanglement was believed to be impossible – or at least paradoxical – given what they knew about physical reality.
But subsequent studies proved how it could happen anyway. Physicist John Stewart Bell made considerable leeway in his 1964 paper that conceived what we now know as Bell’s Theorem. He demonstrated the phenomenon by separating particles so far apart that effects on both could not possibly be caused by local variables, refuting the principle of local realism in quantum mechanics.
But despite his tests, Dr. Bell’s theorem wasn’t proved substantially because of its loopholes – that is, until recently.
Dr. Hanson was among several groups of researchers that found support for Bell’s Theorem in spite of the loopholes. Their performance was published in Nature magazine.
Hanson and his team used a two diamonds, each with a trapped electron in its atomic matrix. Placed about 0.8 mile apart, they were measured in ways that could not be related to hidden variables. And it worked; the electrons indeed correlated with each other.
"The large distance between our detectors ensures that neither the detectors, nor the electrons can exchange information within the time it takes to do the measurement, and so closes the locality loophole," lead author Bas Hensen, a PhD student, explained in a statement. "This is the first time all loopholes are closed at the same time in a single experiment, and we still find that the invisible bond between the electrons is there.”
Krister Shalm, a physicist with the National Institute of Standards and Technology (NIST) in Boulder, Colorado, led another important quantum entanglement last year.
Dr. Shalm and his colleagues used superconducting metal strips at cryogenic temperatures to measure the effects on a pair of entangled photons. Published in the journal of Physical Review Letters, their results were affirmative of Bell’s Theorem.
The team used an analogy to explain the experiment: A and B are entangled photons, or light particles. A is sent to Alice and B is sent to Bob, who are located 607 feet apart. Without consulting each other, Alice and Bob measure properties of the photons using random methods and random number generators. But when they compare their independent experiments, they find that the results are exactly the same.
"It's as if Alice and Bob try to tear the two photons apart, but their love still persists," Shalm said in a statement. "What's exciting is that in some sense, we're doing experimental philosophy.”