Have People Seen Quantum Entanglement With the Naked Eye? It's Complicated

By Veronique Greenwood | May 3, 2011 1:42 pm

photons

What’s the News: Quantum effects like entanglement and superposition are surpassingly strange, and also impossible for humans to see, occurring as they do at the level of subatomic particles. But now researchers have set up an experiment that makes the effects of quantum entanglement visible to the naked eye—at least in theory.

How the Heck:

  • A pair of entangled atoms are intimately and “spookily” linked—even if you move them miles apart, when you poke or prod one, the other will respond as well. Entanglement is usually detected with specialized instruments.
  • But what if entanglement could be made to cause an effect on a scale that even humans could see? This is what University of Geneva researchers wondered when they read about work by an Italian team in which one of a pair of entangled photons was skillfully connected to thousands of other photons, a phenomenon called micro-macro entanglement. That many photons would be something even us giant humans could see.
  • Team leader Nicolas Gisin and his colleagues set up an experiment similar to the Italian one, but instead of using a detector to see whether the photon had entangled the stream of photons and thus passed on its own properties, they used themselves. For hours, they sat in the dark and marked the position of the beam of light emerging from the amplifier to see whether it had been acted on by the initial photon, seeing for themselves the effects of entanglement for the first time.
  • What they saw—or at least what they thought they saw—was that the properties of the single photon were passed onto the thousands of other photons it modified.

Not So Fast: Both teams had suspected that the test they were using to see if entanglement had happened, the Bell test, was faulty when used for large numbers of photons. Gisin proved that that was the case. He deliberately sabotaged the experiment so that entanglement between the photon and the stream of other photons was impossible. Yet the measurements of the light beam’s position still insisted that entanglement had occurred: a false positive. That means that the team might not have seen that micro-macro entanglement after all, and that scientists trying to see it are going to have to devise a new way to detect it.

The Future Holds: Nature News gives a more detailed explanation, but in essence the problem is that no detector will catch every single photon that comes through it. To that end, the Italian team, headed by Fabio Sciarrino, is planning experiments with a laser that will make detection of the stream of photons more accurate. “Unfortunately, we cannot do this experiment with humans as detectors because the laser would burn out their eyes,” Sciarrino says (via NatureNews). Too bad!

Reference: Pomarico, E. , Sanguinetti, B. , Sekatski, P. , Zbinden, H. & Gisin, N. Experimental amplification of an entangled photon: what if the detection loophole is ignored? Preprint available at arXiv:1104.2212v1 (2011).

CATEGORIZED UNDER: Physics & Math
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