Quantum states with equal unlockable correlations and quantum discord

In the context of quantum locking of classical correlations protocols, the condition for equality of the amount of unlockable correlations and quantum discord of general classical-quantum states is investigated. Based on this condition, the structure of such general states is obtained. This condition imposes two constraints on the structure of general classical-quantum states. After presenting the interpretation of these constraints, their role in quantum locking protocols is discussed. Finally, the derived structure is generalized to quantum-quantum states and the amount of their unlockable correlations is interpreted in terms of their symmetric discord.