Can Physicists Make Quantum Entanglement Visible to the Naked Eye?

A pair of quantum entangled photons sure makes a cute couple. Of course, the two might have opposite states--one might be spin up and another spin down, for example--but they promise they'll always stay that way. They're also fiercely loyal, respecting their opposite-spin preferences no matter how long-distance their relationship. (That means that by checking the state of one entangled photon, you can instantly know the state of the other, distant photon, a handy way to "teleport" information.) Unfortunately, because the couple is merely two light particles, their shining example of old romance has been too dim for our eyes to see. Until now. As announced in their recently published Arxiv.org paper, physicists led by Nicolas Gisin at the University of Geneva in Switzerland believe they have found a way to watch this love affair unfold: by boosting the light emitted by one member of a quantum entangled pair, they think they can make this quantum effect visible to a human eye. Measuring quantum states such as spin up or spin down is like looking at whether a switch is on or off. This closely matches the concept of a bit, a single 1 or 0, in computing. With entangled photons, physicists call these on/off states quantum bits or "qubits." What an observer would see while observing an entangled photon is really a choice between two states. The observer could then confirm entanglement by checking to see that the photon was loyal to its partner. In the traditional set-up, two widely separated particle detectors are used to measure the entanglement of the two photons. But Gisin and his colleagues want to let the human eye do some of the work.