Characterization of the non-classical correlations from the dynamical susceptibilities*

Quantum correlations are a central feature in Quantum Information and Quantum Computation. Specifically the Quantum Fisher Information (QFI) is known to be a good indicator of non classical correlation and quantum entanglement in multipartite systems[I].
We obtain a general relationship between an optimized form of QFI (in a 2xN composed Hilbert space), over measurements in the qubit subsystem, and the qubit-qubit susceptibilities in the linear response regime to characterize the non-classical Discord type correlation in the system.We apply the approach to a 2D electron gas with spin-orbit coupling (SO). The relation can be written in terms of the spin- and charge-optical conductivities tensors through the known relations connecting these quantities to the spin-spin susceptibility of
in Rashba and Dresselhaus SO systems[2].This result allows us to obtain a quantification of the quantum discord type correlation of hybrid qubit-other degrees of freedom with the QFI through the calculation of measurable observables associated to the dynamical susceptibilities of the qubit sub-space ( spin, charge, pseudospin in graphene)
[1] P. Hauke et al Nature Physics 12,778 (2016)
[2] P. E. Iglesias y J. A. Maytorena Phys. Rev, B 82, 205324 (2010)