Death and revival of the quantum discord and the measurement-induced disturbance

Abstract

Three different quantifiers, entanglement of formation (ENT), quantum discord (QD), and measurement-induced disturbance (MID), are used to measure the quantum correlations of two qubits in a common squeezed bath. A subspace was found for initial conditions in a squeezed bath, where the system experiences no decoherence. We relate the three measurements with the "distance" from the initial condition to the decoherence free subspace, in order to study the effect of the decoherence in the quantum correlations. We show examples of a system with quantum correlations even when entanglement is null. Furthermore, we study the necessary conditions for the system to become truly classical. We found that, under certain initial conditions and at specific times, the system becomes classical and both the QD and the MID vanish, thus observing the phenomena of sudden death and revival of the quantum correlations. Finally, we observe discontinuities in the QD.

Geometric quantum discord with Bures distance

“…This ordering of quantum correlations is a nice feature of the geometric measures. In contrast, the entanglement of formation E EoF (ρ) can be larger or smaller than the quantum discord δ A (ρ) [46,47].…”