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Journal of Modern Optics

Controlling entanglement dynamics of two qubits coupled to a common reservoir via a coherent field

S. R. J. PATRICK, Fuli Li, Meng Wang, Yang Yang

Published Jan 22, 2010• 2 citations
Publisher

Abstract

We investigate the time evolution of entanglement between two two-level atoms which are coupled to a common multimode electromagnetic reservoir and simultaneously driven by a coherent field. We find that the entanglement can always be created and maintained with a moderate intensity of the driving field during the track of approaching steady entangled states when both atoms are initially in their ground states and the reservoir is in the vacuum state or the squeezed vacuum state. We also show that the steady-state entanglement between the atoms can be enhanced by use of the coherent field when the reservoir is in the weakly squeezed vacuum state. More interestingly, in the squeezed reservoir case, the sudden death period in the time evolution of the entanglement can be removed by use of the coherent driving field.

DOI
10.1080/09500340903548887

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We investigate the time evolution of entanglement between two two-level atoms which are coupled to a common multimode electromagnetic reservoir and simultaneously driven by a coherent field. We find that the entanglement can always be created and maintained with a moderate intensity of the driving field during the track of approaching steady entangled states when both atoms are initially in their ground states and the reservoir is in the vacuum state or the squeezed vacuum state. We also show that the steady-state entanglement between the atoms can be enhanced by use of the coherent field when the reservoir is in the weakly squeezed vacuum state. More interestingly, in the squeezed reservoir case, the sudden death period in the time evolution of the entanglement can be removed by use of the coherent driving field.
Investigates the property of entanglement between a pair of two-level atoms placed in two apart squeezed reservoirs correlated by two-mode squeezed light.Studies the relation of the property to the qubits initial state.The result shows that the sudden death and revival of entanglement of the qubits always occurs between the apart squeezed reservoirs with the time evolution.Never-theless,each the entanglements of various initial state eventually maintains at a same stationry level,has no relationship with the initial state of atom.
The entanglement dynamics of two two-level atoms which are respectively trapped in two independent dissipative single-mode cavities and strongly driven by the classical fields is investigated analytically utilizing the super operator method.It is found that the entanglement is not related to the initial value of the cavity coherent states.The driving field enhances the entanglement sudden death for small dissipation of the cavity,while it protects the entanglement from sudden death for large dissipation in the presence of strong driving field.These results show that even in the bad cavity(with large decay rate),the entanglement can be free from sudden death with the assistance of classical driving field.
Entanglement plays a crucial role in quantum information protocols; thus the dynamical behavior of entangled states is of great importance. In this paper, we suggest a useful scheme that permits a direct measure of entanglement in a two-qubit cavity system. It is realized through cavity-QED technology utilizing atoms as flying qubits. To quantify entanglement we use the concurrence. We derive the conditions that ensure that the state remains entangled in spite of the interaction with the reservoir. The phenomenon of entanglement sudden death in a bipartite system subjected to a squeezed vacuum reservoir is examined. We show that the sudden death time of the entangled states depends on the initial preparation of the entangled state and the parameters of the squeezed vacuum reservoir.
The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.
We consider two two-level atoms fixed at different positions, driven by a monochromatic laser field, and interacting collectively with the vacuum electromagnetic field. A Born-Markov-secular master equation is used to describe the dynamics of the two atoms and their steady-state is obtained analytically for two configurations, one in which the atoms are in equivalent positions and another in which they are not. The steady-state populations of the energy levels of the free atoms, entanglement, quantum discord and degree of mixed-ness are calculated analytically as a function of the laser field intensity and the distance between the two atoms. It is found that driving both atoms with the laser field is inefficient for the generation of steady-state correlations when they are in equivalent positions. On the contrary, inequivalent positions lead to the possibility of considerable steady-state entanglement and left/right quantum discord. It is shown that an X-state can be obtained for high laser field intensities for both configurations. This allows the comparison of two measures of quantum discord. The behaviour and relationships between correlations are studied and several limiting cases are investigated.
Within the framework of semi-classical theory of light and matter, we investigate the entanglement dynamics of the bipartite system consisting of two identical and interacting two-level atoms by means of concurrence, which are coupled to the common reservoir and driven by external time-dependent laser field. Numerical results reveal that for these initially entangled states, the bipartite system undergoes entanglement sudden death (ESD) and birth (ESB), and stable entanglement always occur irrespective of dissipation. Besides, the coupling strength of the electric dipole-dipole will have remarkable effects on the entanglement dynamics, like accelerating the ESD and ESB. However, these conclusions are not applicable to other initially entangled states.