Physicists Create Quantum Link Between Photons That Don't Exist at the
Same Time
>
http://news.sciencemag.org/sciencenow/2013/05/physicists-create-quantum-link-b.html?ref=em
> Now they're just messing with us. Physicists have long known that
> quantum mechanics allows for a subtle connection between quantum
> particles called entanglement, in which measuring one particle can
> instantly set the otherwise uncertain condition, or "state," of
> another particle -- even if it's light years away. Now, experimenters
> in Israel have shown that they can entangle two photons that don't
> even exist at the same time.
>
> "It's really cool," says Jeremy O'Brien, an experimenter at the
> University of Bristol in the United Kingdom, who was not involved in
> the work. Such time-separated entanglement is predicted by standard
> quantum theory, O'Brien says, "but it's certainly not widely
> appreciated, and I don't know if it's been clearly articulated
> before."
>
> Now Eli Megidish, Hagai Eisenberg, and colleagues at the Hebrew
> University of Jerusalem have entangled two photons that don't exist
> at the same time. They start with a scheme known as entanglement
> swapping. To begin, researchers zap a special crystal with laser
> light a couple of times to create two entangled pairs of photons,
> pair 1 and 2 and pair 3 and 4. At the start, photons 1 and 4 are not
> tangled. But they can be if physicists play the right trick with 2
> and 3.