engleski

Quantum Simulators and Quantum Repeaters

It is shown that a photon from a non-maximal singlet, obtained by a controlled entanglement of two downconverted photon pairs, can be entangled with a photon from another such singlet. As a result the other photons from the singlets appear in a singlet state with an event probability arbitrary close to one. This is due to the fact that in such an entanglement the probability of control photons coming out from the same side of a beam splitter can be made arbitrary small. By means of subpicosecond lasers with nanosecond oscillations locked to a master clock one can use the property to construct quantum repeaters for communication of EPR pairs. Possible applications in teleportation, quantum cryptography, loophole-free Bell experiment, and quantum computers are discussed. As for quantum computers, we consider quantum simulators able to directly simulate quantum systems. We show that such computers require a general machine language which goes beyond the standard quantum gate algebra. We present several conditions which the latter algebra must additionally satisfy.

quantum computers; quantum repeaters; quantum optics; quantum logic

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