Experimental realization of the quantum universal NOT gate

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Authors

DEMARTINI Francesco BŮŽEK Vladimír SCIARRINO F. SIAS C.

Year of publication 2002
Type Article in Periodical
Magazine / Source Nature
MU Faculty or unit

Faculty of Informatics

Citation
Field Theoretical physics
Keywords optimal manipulations with quantum information; universal quantum machines; quantum cloning
Description In classical computation, a ``bit'' of information can be flipped (that is, changed in value from zero to one and vice versa) using a logical NOT gate; but the quantum analogue of this process is much more complicated. A quantum bit (qubit) can exist simultaneously in a superposition of two logical states with complex amplitudes, and it is impossible to find a universal transformation that would flip the original superposed state into a perpendicular state for all values of the amplitudes. But although perfect flipping of a qubit prepared in an arbitrary state (a universal NOT operation) is prohibited by the rules of quantum mechanics, there exists an optimal approximation to this procedure. Here we report the experimental realization of a universal quantum machine(4) that performs the best possible approximation to the universal NOT transformation. The system adopted was an optical parametric amplifier of entangled photon states, which also enabled us to investigate universal quantum cloning.
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