Revival of quantum correlations without system-environment back-action

Understanding the dynamics of correlations in quantum systems is essential for quantum
information and quantum computation. The dynamics of entanglement in bipartite open quantum
systems and its dependence on the interaction with quantum environments, with the appearance of
phenomena such as sudden death, revivals and trapping, can be considered well understood in
general [1,2]. Recently, attention has moved to the dynamics of correlations other than
entanglement, like quantum discord, in the presence of either Markovian and non-Markovian [3]
quantum environments. In the case of initially entangled noninteracting qubits in independent non-
Markovian quantum reservoirs, the peculiar occurrence of entanglement revivals has been explained
in terms of transfer of correlations back and forth from the two-qubit system to the various parts of
the total system [4]. This is connected to the back-action of the system on the environment which
creates correlations between qubits and environments and between the environments themselves.
In this talk I address the issue of the possible occurrence of revival of quantum correlations even in
absence of system-environment back-action. In particular the talk consists of two parts. In the first
one, of introductory nature, I will discuss the characterization of various kinds of correlations
present in a given quantum state and I will summarize some known results about the dynamics of
correlations in open quantum systems. In the second one, I will discuss some of the results
presented in Ref.[5]. In particular, I will consider a system consisting of a pair of independent qubits
driven by a system-unaffected environment, where no back-action mechanism can transfer
correlations from system to the environment. I will show that revivals of correlations may
nevertheless occur in this system. To interpret these revivals by looking only at intrinsic features of
the reduced dynamics of the two qubits, I will consider a quantifier of non-Markovianity, showing
that the revivals are connected to its increase.

References:
[1] B. Bellomo, R. Lo Franco and G. Compagno, Phys. Rev. Lett. 99, 160502 (2007);
[2] B. Bellomo, R. Lo Franco, S. Maniscalco and G. Compagno, Phys. Rev. A 78, 060302(R) (2008);
[3] F. F. Fanchini et al., Phys. Rev. A 81, 052107 (2010);
[4] C. E. Lopez et al., Phys. Rev. Lett. 101, 080503 (2008);
[5] R. Lo Franco, E. Andersson, B. Bellomo and G. Compagno, arXiv:1009.5710.