puter is much simpler on paper than in practice, though, and it will doubtless be decades before you’ll be able to buy one at Best Buy.
Nevertheless, simple quantum computations can be performed now. In fact, factoring 15 has been achieved with a quantum computer based on the same technology used in MRI medical imaging. And in 2002 Chinese physicists reported an experimental demonstration of the quantum Prisoner’s Dilemma game, using a simple quantum computer. In the following year, Chinese physicists Lan Zhou and Le-Man Kuang outlined how to set up a quantum game communication system using lasers and mirrors and other optical devices in a paper published in Physics Letters A.5
The Zhou-Kuang design exploits one of the most mysterious features of quantum physics, a ghostly bond between particles that have emerged from a mutual interaction. When two particles of light (photons) are emitted simultaneously from the same atom, for example, they retain an ethereal connection—measuring one seems to affect the other even if it is meters, miles, or light-years away. This connection is called “entanglement,” and it’s one of the things about quantum mechanics that really bothered Einstein (he called it “spooky action at a distance”).
When two photons are entangled, they share quantum information in a peculiar way. If you think of them as spinning coins, they both keep spinning—becoming neither heads nor tails—until one of them is observed. And then the other one stops spinning, too! So suppose I possess two pennies, spinning within opaque boxes, entangled in such a way that if one is observed to be heads, the other will turn up tails. I send one box via FedEx to my sister in Ohio. She can’t resist opening the package right away and discovers the penny on the bottom of the box, showing heads. The instant she sees it, the penny in my remaining box stops spinning and shows tails—whether I’m in Texas or California or on the International Space Station. Even if I don’t look in my box, I know damn well that the penny shows tails (once my sister has called to