Quantum Teleportation

Anton Zeilinger

This year the Nobel Prize in Physics has been awarded to John Clauser, Alain Aspect and Anton Zeilinger, for their pioneering work in quantum communications.

• Clauser (with Stuart Freedman, who died in 2012) carried out the first experiment with entangled photons in 1972, which proved that the direction of Bell's inequality favors the Copenhagen interpretation of quantum mechanics, thus solving the EPR paradox (acronym for Einstein-Podolsky-Rosen), which tried to contradict this interpretation. This experiment was not complete, so others were carried out later, under increasingly strict conditions.

A few clarifications on the quantum revolution

First of all, let as clarify a few concepts, for recent news published in the media tends to encourage confusion.

·         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.

·         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.