A FUNDAMENTAL limitation of classical communication channels is that a two-state system can only transmit one bit of information: one state represents 0s and the other represents Is. If the information carrier is a quantum system, however, theory holds that this is no longer true. Anton Zeilihger and colleagues at the University of Innsbruck have now provided experimental evidence for this theoretical idea (k Mattle et al. 1996 Phys. Rev. lett. 76 4656). They used a two level quantum system, the polarization of a single photon, to send a "trit" of information. A trit has three possible values-0,1 or 2-and is equivalent to 1.58 bits.
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