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Qubit: the
quantum unit of information. While classical information is expressed in bits,
which may take only the values 0 or 1, qubits are formed by superposition (or
linear combination) of two quantum states, |0> and |1> (i.e. the horizontal
or vertical polarization of a photon) and its value is: α|0>+β|1>, where α and β are two complex numbers called probability amplitudes.
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Quantum Cryptography: It
encrypts information through a protocol that takes advantage of the quantum
properties of matter. The procedures devised so far can be deciphered by opponents
using quantum procedures, but it is known (or believed) that they are
impossible to decipher by classical means. The first quantum
cryptography protocol, BB84, was proposed in 1984 by Charles Bennett and Gilles
Brassard of IBM.
