Quantum entanglement in a pure state of strongly correlated quantum impurity systems

We consider quantum entanglement in strongly correlated quantum impurity systems for states manifesting interesting properties such as the multilevel Kondo effect and dual nature between itineracy and localization. etc. For this purpose, we set up a system consisting of one or two quantum impurities arbitrarily selected from the system as a subsystem and investigate quantum entanglement with its environmental system. We reduce the pure state of interest as described above to the subsystem, and formulate quantum informative quantities such as entanglement entropy, mutual information, and relative entropy. To demonstrate the potential of the method proposed here, we apply them to a dimer with several types of internal interaction, short Hubbard chains, and the single impurity Anderson model to study the relationship between their states and the behaviors of quantum informative quantities. The obtained results suggest that the method proposed here is promising for elucidating the quantum entanglement of pure states in various quantum impurity systems.