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Updated: Apr 21, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Complete positivity, Markovianity, and the quantum data-processing inequality, in the presence of initial
1Graduate School of Information Science, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan.
Abstract:
We show that complete positivity is not only sufficient but also necessary for the validity of the quantum data-processing inequality. As a consequence, the reduced dynamics of a quantum system are completely positive, even in the presence of initial correlations with its surrounding environment, if and only if such correlations do not allow any anomalous backward flow of information from the environment to the system. Our approach provides an intuitive information-theoretic framework to unify and extend a number of previous results.
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