Generalizations of quantum discord

When Alice and Bob share two pairs of quantum correlated states, Alice can remotely prepare quantum entanglement and quantum discord in Bob’s side by measuring the parts in her side and telling Bob the measurement results by classical communication. For remote entanglement preparation, entanglement is necessary . We find that for some shared resources having the same amount of entanglement, when Bell measurement is used, the entanglement remotely prepared can be different, and more discord in the resources actually decreases the entanglement prepared. We also find that for some resources with more entanglement, the entanglement remotely prepared may be less. Therefore, we conclude that entanglement is a necessary resource but may not be the only resource responsible for the entanglement remotely prepared, and discord does not likely to assist this process. Also, for the preparation of discord, we find that some states with no entanglement could outperform entangled states.

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Steady-state correlations of two atoms interacting with a reservoir

Quantum Information and Computation ◽

10.26421/qic12.3-4-4 ◽

2012 ◽

Vol 12 (3&4) ◽

pp. 231-252

Author(s):

Luis Octavio Castanos

Keyword(s):

Electromagnetic Field ◽

Steady State ◽

Master Equation ◽

Field Intensity ◽

Mixed State ◽

Laser Field ◽

Quantum Discord ◽

Energy Levels ◽

High Laser ◽

X State

We consider two two-level atoms fixed at different positions, driven by a resonant monochromatic laser field, and interacting collectively with the quantum electromagnetic field. A Born-Markov-secular master equation is used to describe the dynamics of the two atoms and the steady-state is obtained analytically for a configuration of the atoms. The steady-state populations of the energy levels of the free atoms, entanglement, quantum and geometric discords and degree of mixedness are calculated analytically as a function of the laser field intensity and the distance between the two atoms. It is found that there is a possibility of considerable steady-state entanglement and left/right quantum discord and that these can be controlled either by increasing/decreasing the intensity of the laser field or by increasing/decreasing the distance between atoms. It is shown that the system of two atoms can be prepared in a separable mixed state with non-zero quantum discord that turns into an $X$-state for high laser field intensities. The behavior and relationships between the different correlations are studied and several limiting cases are investigated.

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Quantum discord and entanglement of two atoms in a micromaser-type system

Modern Physics Letters B ◽

10.1142/s0217984916501906 ◽

2016 ◽

Vol 30 (15) ◽

pp. 1650190

Author(s):

Xue-Qun Yan ◽

Fu-Zhong Wang

Keyword(s):

Time Evolution ◽

Mixed State ◽

Quantum Discord ◽

Type System ◽

Complete Loss ◽

Entangled State ◽

Fock State

The correlations dynamics of two atoms in the case of a micromaser-type system is investigated. We show that the entangled state can be created by initially maximally mixed state and there exist collapse and revival phenomena for the time evolutions of both entanglement and quantum discord under the system considered as the field is initially in the Fock state. Our results confirm that entanglement and quantum discord have similar behaviors in certain time ranges, such as their oscillations during the time evolution being almost in phase, but they also present significant differences, such as quantum discord being maintained even after the complete loss of entanglement. Furthermore, we exhibit clearly that the dynamics of quantum discord under the action of environment are intimately related to the generation and evolution of entanglement.

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