Swiss Scientists Perform Massive Test of 80-Year-Old, Spooky Quantum Paradox

October 31, 2018

A team of Swiss scientists conducted a massive test of one of the strangest paradoxes in quantum mechanics, a huge example of the kind of behavior Einstein suspected, which Einstein called “spooky action at a distance.”

The story begins more than 80 years ago. Back in 1935, Albert Einstein and physicists Boris Podolsky and Nathan Rosen discovered something strange. They entangled two particles – we’ll call them Alice and Bob – so that their physical properties were connected even at great distances, and anything you did to one particle would affect the other. Intuitively, you’d think that if you had access to Alice, you’d know more about her than you would about Bob, who is a great distance away. That’s what you’d expect, since Einstein’s laws of relativity in physics are on a large scale. But the trio of physicists discovered something strange, now known as the Einstein-Podolsky-Rosen (EPR) paradox: by studying Alice, you actually learn more about Bob than you do about Alice.

Later experiments with single particles proved that physicists were right on this point. But this new experiment, published today (April 26) in the journal Science, shows that the effect still happens even when using a clump of nearly 600 ultracold particles.

It’s not surprising, exactly, that the paradox that was originally framed in terms of two particles would also occur in a clump of hundreds of particles. The same physics that works in a very small system should also work in a much larger system. But scientists conduct these increasingly complex tests because they help confirm old theories and narrow down the ways in which they might be wrong. They also demonstrate the ability of modern technology to put into action ideas that Einstein and his colleagues could only think about in the abstract.

To do this experiment, the researchers cooled about 590 rubidium atoms (given 30 atoms) to the edge of absolute zero.

At that temperature, the atoms formed a state of matter known as bose-Einstein condensates, which, as Live Science previously reported, is a state of matter in which a large group of atoms becomes so entangled that they begin to blur and overlap with each other; they begin to behave more like one large particle than many separate particles. Quantum physicists like to experiment with Bose-Einstein condensates because this matter tends to demonstrate the weird physics of the quantum world on a large enough scale that scientists can observe it directly.

In this experiment, they used high-resolution imaging to measure the spins of different masses within a soup of rubidium atoms. The atoms in the condensate are so entangled that physicists can predict the behavior of the second block by studying just the first atom. They showed that both atoms are so entangled that the behavior of the second atom is actually easier to know when only the first atom is observed, and vice versa.

The EPR paradox has come alive, and it is larger for the quantum world.