Physicists at the University of Geneva in Switzerland have devised a new kind of quantum experiment using humans as photon detectors, and in doing so have made the quantum phenomenon of entanglement visible to the naked eye for the first time.
For those that need a primer, entanglement is that strange quantum phenomenon that links two particles across distances such that any any measurements carried out on one particle immediately changes the properties of the other--even if they are separated by the entire universe. Einstein called it “spooky action at a distance.” And indeed it is weird.Nicolas Gisin at U. of Geneva noted that Italian physicists had previously done an interesting thing with entangled photons. Rather than entangling just a few as experimenters usually do, the Italian team had entangled a pair of photons and then amplified one of them to create a photon shower containing thousands of particles, all linked to the single other photon from the original pair. That is, there was one “microscopic” photon, and a shower of “macroscopic” photons, all tied together at the quantum level.
Gisin realized that while the naked eye can’t see a single photon, it can certainly see thousands. So he used a setup similar to the Italians’, but rather than putting a photon detector in front of the macroscopic photons he put himself and his colleagues there. The beam of photons produced by the amplifier would appear in one of two positions in their darkened room, depending on the polarization state given to their microscopic single photon. Time after time, when the human results were tested against photon detectors, they got a positive result.
It may sounds like a bunch of scientists sitting in a dark room looking at blinking lights, but it represents the first time quantum entanglement has been directly observed with the naked eye.