Process reconstruction: From unphysical to physical maps via maximum likelihood

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Authors	ZIMAN Mário PLESCH Martin BUŽEK Vladimír ŠTELMACHOVIČ Peter
Year of publication	2005
Type	Article in Periodical
Magazine / Source	Physical Review A
MU Faculty or unit	Faculty of Informatics
Citation
Field	Theoretical physics
Keywords	quantum process reconstruction
Description	We show that the method of maximum likelihood (MML) provides us with an efficient scheme for the reconstruction of quantum channels from incomplete measurement data. By construction this scheme always results in estimations of channels that are completely positive. Using this property we use the MML for a derivation of physical approximations of unphysical operations. In particular, we analyze the optimal approximation of the universal NOT gate as well as the physical approximation of a quantum nonlinear polarization rotation.
Related projects:	Quantum Resources and primitives Highly Parallel and Distributed Computing Systems