A Condition for the Nullity of Quantum Discord

Understand

The positivity of quantum discord is shown to be equivalent to the strong subadditivity of von-Neumann entropy.

• This leads us to a necessary and sufficient condition characterizing the set of states with zero quantum discord.
• This also gives us a mathematical definition of pointer states, as they are the states with zero discord.
• Finally, we suggest that strong subadditivity of entropy might delineate the boundaries of the set of quantum correlations.