16. Quantum Teleportation Leaps Toward Reality
It's not exactly "Beam me up, Scotty," but for the first time scientists have teleported information between light and atoms, hastening the long-awaited advent of ultrafast quantum computers and unbreakable encryption schemes. Quantum teleportation is the process of making a subatomic particle's physical state vanish from one place and appear in another, a little like Captain Kirk's transporter. What makes this possible is a bizarre phenomenon known as entanglement, in which a pair of particles have complementary characteristics, such as two electrons spinning in opposite directions. The irreducible uncertainty of quantum mechanics makes it impossible to predict the state of a given electron, but because the two particles are entangled, measuring the state of one automatically determines the state of the other, regardless of how far apart they are.
In order to teleport a state between light and atoms, Eugene Polzik and his colleagues at the Niels Bohr Institute in Copenhagen, in collaboration with Ignacio Cirac of the Max Planck Institute for Quantum Optics in Germany, entangled a light beam with a magnetized gas of cesium atoms. The researchers then encoded the state they wanted to teleport into the light beam with laser pulses. By separating the entangled quantum information from the light beam and uncovering the laser message, the team was able to teleport the complementary state to the atoms at a distance of half a yard. "For the first time," Polzik says, quantum teleportation "has been achieved between light—the carrier of information—and atoms." This was also the first time that it was done with a macroscopic atomic object acting as the target. Scientists had previously teleported states only between pairs of photons or pairs of atoms. But a practical quantum computer, Polzik notes, requires the transfer of information between a data stream, such as light, and a stored quantum state, such as the atoms in a hard drive.
