The major players include Klaus Mattle and Harald Weinfurter at Innsbruck, and Paul Kwiat, now at the Los Alamos National Laboratory. That group applies quantum encoding to photons, particles of light. You can think of a photon's polarization as the direction in which its electric field vibrates, and it can be changed in a number of ways. For instance, a horizontally polarized photon can be directed through an optical device that rotates its angle of polarization by 90 degrees, thereby converting it to a vertically polarized photon. To change the state of two photons by manipulating one of them, an investigator must confront some quantum-mechanical complications.
Entanglement is considered by many to be the most puzzling feature of quantum mechanics.
Quantum entanglement essentially means that the state of one quantum system is inexorably linked to the state of another quantum system. In the case of polarization, one photon's direction of polarization depends on the other photon's direction of polarization and the state of the pair. For example, a pair's state may require that the photons have perpendicular polarizations. Encoding an entangled pair, however, achieves only half of the desired result. Next, the pair's state must be determined or read.