Thermal quantum discord and classical correlations in a two-qubit Ising model under a site-dependent magnetic field

We investigate the thermal quantum discord and classical correlations in a two-qubit Ising model interacting with a site-dependent external magnetic field. Systematic study of all correlations is performed for various values of the system's temperature, and the magnetic field magnitude and direction on each site. Our results reveal interesting findings as regrowth regions of the classical and quantum correlations. Moreover unexpected bahavior as for example increase of the quantum correlations with the increase of the anisotropy of the applied magnetic fields for specific values of the external parameters is reported. By comparing our quantum discord data with the entanglement of formation, we have concluded that the major source of quantum correlations is the entanglement. Overall, we have found that the independent control of each spin site by external fields is a very practical and robust way of achieving significant quantum discord useful in quantum computation and information proccesses.