New Quantum Experiment Reveals 'Spooky Action at a Distance' for the First Time

A new experiment has first the first time ever demonstrated Albert Einstein's original conception of "spooky action at a distance" with the use of a single particle. The scientists used homodyne measurements to show what Einstein did not believe to be real: the non-local collapse of a particles wave function.

According to quantum mechanics, a single particle can be described by a wave function that spreads over arbitrarily large distances, but is never detected in two or more places. This phenomenon is actually explained in quantum theory by what Einstein described as "spooky action at a distance," or the instantaneous, non-local collapse of the wave function to wherever the particle is detected.

In this latest experiment, the researchers split a single photon between two laboratories and, using homodyne detectors-which measure wave-like properties-they've shown that the collapse of the wave function is a real effect. In fact, this phenomenon is the strongest proof yet of the entanglement of a single particle, an unusual form of quantum entanglement that is being increasingly explored for quantum communication and computation.

"Einstein never accepted orthodox quantum mechanics and the original basis of his contention was this single-particle argument," said Howard Wiseman, one of the researchers, in a news release. "This is why it is important to demonstrate non-local wave function collapse with a single particle. Einstein's view was that the detection of the particle only ever at one point could be much better explained by the hypothesis that the particle is only ever at one point, without invoking the instantaneous collapse of the wave function to nothing at all other points. However, rather than simply detecting the presence or absence of the particle, we used homodyne measurements enabling one party to make different measurements and the other, using quantum tomography, to test the effect of those choices."

The findings are published in the journal Nature Communications.

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