Publication details

Estimation of potentially unphysical maps

Authors

PLESCH Martin ZIMAN Mário BUŽEK Vladimír ŠTELMACHOVIČ Peter

Year of publication 2006
Type Article in Periodical
Magazine / Source Open Systems & Information Dynamics
MU Faculty or unit

Faculty of Informatics

Citation
Field Theoretical physics
Keywords unphysical maps;
Description When standard methods of process (black-box) estimation are applied straightforwardly then it may happen that some sets of experimental data result in unphysical estimations of the corresponding channels (maps) describing the process. To prevent this problem, one can use the method of maximum likelihood (MML), which provides an efficient scheme for reconstruction of quantum channels. This scheme always results in estimations of channels that are fully physical, e.g. the corresponding maps are linear, positive and completely positive. To show this property, we use the MML for a derivation of physical approximations of truly unphysical operations. In particular, we analyze physical approximations of the universal-NOT gate, the quantum nonlinear polarization rotation and the map $\rho -> \rho^2$. Given the result of MML, we examine retrospectively the quality of the experiment. Depending on the resulting value of the MML functional we can determine (physical) consistency of the input data.
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