Measuring the degree of unitarity for any quantum process
Department of Physics and Center of Theoretical and Computational Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
Received: 7 May 2014
Received in final form: 18 June 2014
Published online: 11 September 2014
We establish a general theory for measuring the degree of unitarity (DU) of any quantum process, in which the DU is defined to be the fidelity between the process and its closest unitary one. The DU, as an intrinsic property of a given quantum process, is able to quantify the distance between the process and the group of unitary ones, being closely related to the noise of this quantum process. We not only derive analytical results of DU for qubit unital channels, but also find the lower and upper bounds in general cases. It is shown that the lower bound is tight for most of quantum processes. Moreover, the relationship between the DU of any quantum process and its non-markovian behavior is also addressed.
Key words: Quantum Information
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2014