LAUSR

We propose a reliable analytical method to evaluate the non-classical correlations based on linear entropy for an arbitrary qudit–qubit quantum state. The linear entropy is used to overcome the difficulty of the maximization of the classical correlations encountered when the von Neumann entropy is used in determining quantum discord. The quantum discord based on linear entropy is employed to derive the amount of quantum correlations in a qutrit–qubit mixed spin system in the thermal equilibrium at temperature T . We investigate also the situation when the system is embedded in an external magnetic field. The obtained amount of quantum discord is then compared with the measurement-induced disturbance (MID) and logarithmic negativity. The analysis shows that both QD and MID are more robust than entanglement. Besides, QD and MID can be exploited to determine the critical points of quantum phase transitions in the system.