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.

Timeline

Poster of the film based on Timeline

In 1999, Michael Crichton published his novel Timeline, a typical science fiction novel about time travel, whose plot can be summarized as follows:

A research company has developed a procedure to travel into the past. Using it, they sent to 14th century France, in the midst of the 100 Years War, a history professor who is conducting archaeological studies in ruins near the medieval fortress of La Roque. His collaborators, who do not know what is happening, find among the ruins a call for help from the professor, which when subjected to carbon-14 dating turns out to come from the 14th century. Picked up by the company that sponsors their studies, they are sent into the past to save the professor, who cannot return on his own.

In another post in this blog, I discussed the paradoxes that can be caused by traveling into the past, and various procedures invented by scientists and writers to escape them. In the novel, Crichton mentions two:

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.