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Physica Scripta

Generation of quantum correlations for two qubits through a common reservoir

M. Angeles Gallego, Raúl Coto, Miguel Orszag

Published Feb 1, 2012• 5 citations
Publisher

Abstract

Recently, besides entanglement, an entropy-based measurement called quantum discord has been used to describe the quantum correlations in separable and non-separable states. Here we compare the dynamics of entanglement with that of quantum discord, in the case of two qubits in a common thermal or squeezed reservoir. We focus on the generation of quantum correlations, starting from an uncorrelated system.

DOI
10.1088/0031-8949/2012/t147/014012

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Recently, besides entanglement, an entropy-based measurement called quantum discord has been used to describe the quantum correlations in separable and non-separable states. Here we compare the dynamics of entanglement with that of quantum discord, in the case of two qubits in a common thermal or squeezed reservoir. We focus on the generation of quantum correlations, starting from an uncorrelated system.
"or many years the entangled systems have been associated to the quantum world, while the separable systems with the classical world. Recently quantum discord showed that some separable states posses quantum correlation even when the entanglement is zero. In this work, we compare different features of quantum discord and entanglement of formation for two qubits in a common squeezed reservoir. We relate the quantum correlations with the “distance” of our initial condition from the decoherence free subspace where the system is not affected by environment. While for some initial conditions, the entanglement presents sudden death and revival, quantum discord does not. Still, is not clear the relation between these two measurements of “quantumness”."
In this paper, we have investigated the dynamics of the quantum correlation between two qubits of a system composed of an arbitrary number of qubits dissipating into a common environment. Our results imply that, when the initial state of the system contains one excitation, the quantum correlation of the quantum discord and the entanglement of formation can be generated between two qubits which have no interaction with each other but are interacting with a common environment. From our analysis, we find that the dynamics of the quantum discord and the entanglement of formation depends not only on the scaled time but also on the size of the system. The larger the size of the system is, the less the quantum discord and the entanglement of formation is generated. By using a comparison between the quantum discord and the entanglement of formation, we find that the quantum discord is more robust to the size of the system than the entanglement of formation is, in the sense that the former decreases more slowly with an increase of the size of the system than the latter does. In addition, the case of the initial state with two excitations is discussed.
We describe the generation of quantum correlations (entanglement, discord and steering) in a system composed of two coupled non-resonant bosonic modes immersed in a common thermal reservoir, in the framework of the theory of open systems. We show that for separable initial squeezed thermal states entanglement generation may take place, for definite values of squeezing parameter, average photon numbers, temperature of the thermal bath, dissipation constant and strength of interaction between the two bosonic modes. We also show that for initial uni-modal squeezed states Gaussian discord can be generated for all non-zero values of the strength of interaction between the modes. Likewise, for an initial separable state, a generation of Gaussian steering may take place temporarily, for definite values of the parameters characterizing the initial state and the thermal environment, and the strength of coupling between the two modes.
We evaluate the quantum discord dynamics of two qubits in independent and common non-Markovian environments. We compare the dynamics of entanglement with that of quantum discord. For independent reservoirs the quantum discord vanishes only at discrete instants whereas the entanglement can disappear during a finite time interval. For a common reservoir, quantum discord and entanglement can behave very differently with sudden birth of the former but not of the latter. Furthermore, in this case the quantum discord dynamics presents sudden changes in the derivative of its time evolution which is evidenced by the presence of kinks in its behavior at discrete instants of time.
In this work, we study the dynamics of quantum correlation (QC) in terms of quantum discord and its transfer for multiqubit systems in dissipative environments. At first, we investigate the dynamics of bipartite QC contained in a three-qubit system that are initially prepared in an extended W-like state with each qubit coupled to an independent reservoir. Subsequently, we study a realistic quantum network of several remote nodes each of which contains two qubits in contact with a common reservoir. For the simplest case of two nodes, we study the dynamics of QC and its transfer from the initially correlated system to the reservoirs and other degrees of freedom. In both models, we pay particular attention to the independent evolution and transfer of QC without the participation of entanglement when the systems of interest are initially prepared in unentangled states. We also observe the occurrence of sudden changes of quantum discord when the systems are initially in mixed states.
Abstract The dynamics of entanglement and quantum discord (QD) between two two-level atoms interacting with two dissipative coupled cavities in the presence of initial atom-cavity correlations is investigated. In comparison with the result of the initial factorized state, we show that the initial state contained quantum correlation of atom-cavity is most robust against the dissipative environment, and the initial atom-cavity correlations, especially the quantum correlation, play a constructive role in the generation of atomic entanglement and QD. Simultaneously, the comparison between Markovian and non-Markovian dynamics, and the influences of inter-cavity hopping rate are also taken into account and analyzed.