Quantum correlations as precursors of entanglement

Abstract

We show that for two initially excited qubits, interacting via dipole forces and with a common reservoir, entanglement is preceded by the emergence of quantum and classical correlations. After a time lag, entanglement finally starts building up, giving rise to a peculiar entangled state, with very small classical correlations. Different measures of quantum correlations are discussed, and their dynamics are compared and shown to lead to coincident values of these quantifiers for several ranges of time.

Evolution of quantum correlations in a two-atom system

“…For short times the quantum discord increases, reaches the maximum and goes down to the minimum in order to increase again to the subsequent maximum, and eventually it goes down to zero asymptotically. This behaviour has been reported in [32]. The concurrence remains zero up to Γt ∼ 4 and next abruptly becomes nonzero, the effect that has been referred to as sudden birth of entanglement [12].…”

Characterization of correlations in two-fermion systems based on measurement induced disturbances

“…Indeed, as was established in a pioneering work by Zurek and Ollivier [17], even separable mixed states can be endowed with correlations exhibiting non-trivial quantum features. In the case of systems consisting of distinguishable parts various measures have been advanced to characterize quantitatively the different ways (besides entanglement) in which quantum correlations can manifest themselves [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Prominent among these are quantum discord and the measures of correlations based upon the disturbances of quantum states due to local measurements proposed by Luo [21][22][23] and by SaiToh and collaborators [28,29].…”

Bipartite entanglement induced by classically-constrained quantum dissipative dynamics

“…Similarly to the Dicke model [23,36], Fig. 1 also shows that for all mixed states (λ = ±1) there exist a time delay before entanglement emerges.…”

“…Eq. (36) (36). Trivially, the eigenvectors of H are defined by the external product of the eigenvectors of σ x , that is |x ± ⊗ |x ± with eigenvalues ±Ω = ±(Ω A + Ω B )/2, and |x ± ⊗ |x ∓ with eigenvalues ±δΩ = ±(Ω A − Ω B )/2.…”

“…The entanglement is characterized both in the transitory and stationary regimes. In order to provide an deeper char-acterization of the dynamics, added to the entanglement behavior, we also study its relation with the quantum and classical correlations build up between both systems [36][37][38][39][40].…”