Experimental realization of the quantum universal NOT gate

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 st...

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Bibliographic Details
Published in:Nature (London) 2002-10, Vol.419 (6909), p.815-818
Main Authors: De Martini, F., Bužek, V., Sciarrino, F., Sias, C.
Format: Article
Language:English
Subjects:
Applied sciences
Circuit properties
Cloning
Digital circuits
Electric, optical and optoelectronic circuits
Electronic circuits
Electronics
Exact sciences and technology
Humanities and Social Sciences
letter
multidisciplinary
Particle physics
Quantum theory
Science
Science (multidisciplinary)
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Summary: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 1 , 2 , 3 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 2 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.
ISSN:0028-0836
1476-4687
DOI:10.1038/nature01093