Weak measurement induced super discord can resurrect lost quantumness

Abstract: The projective measurement usually destroys the quantum correlation between two subsystems of a composite system, thereby making the measured state useless for any efficient quantum information processing and quantum computation task. The weak measurement acts gently on quantum system and do not force the system state to decohere completely, thus revealing the super quantum discord, which can take value more than that of the normal quantum discord. Remarkably, we prove that the super quantum discord in the post measured state is equal to the difference between the super quantum discord and the normal quantum discord in the original state. Thus, the weak measurement has the ability to resurrect the lost quantumness of any composite quantum state. This suggests a conservation law for the extra quantum correlation in any composite state. The amount of extra quantum correlation which is destroyed by the projective measurement in the original state is equal to the amount of extra quantum correlation captured by the weak measurement in the post-measured state.