Super-quantum discord in ferromagnetic and antiferromagnetic materials

Abstract

Super-quantum discord is an extension of the quantum discord concept where weak measurements are made instead of projective measurements. We study the temperature behavior of the super-quantum discord for two real magnetic materials. We extract information about super-quantum discord from the magnetic susceptibility data for iron nitrosyl complexes $\mathrm{ Fe_2(SC_3 H_5N_2)_2(NO)_4}$ and binuclear Cu(II) acetate complex $\mathrm{[Cu_2 L(OAc)]\cdot 6 H_2O}$, where $\mathrm{ L}$ is a ligand that allows us to compare the super-quantum discord with the standard one. The dependence of the super-quantum discord on the parameter describing weak measurements is studied. Obtained difference between super-quantum and quantum discords confirms the detection of additional quantum correlations that are usually destroyed during projective measurements. The use of the approach allows to predict quantitatively in advance the advantages of use of weak measurements versus projective one for quantum technologies in real settings where quantum discord is used as resource. This can be relevant particularly in macroscopic quantum systems where weak measurements can be used to extract information about the system.