Physicists Create Quantum Link Between Photons That Don't Exist at the Same Time: 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.