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Chinese Physics

Entropy evolution properties in a system of two entangled atoms interacting with light field

Tang-Kun Liu, Ji‐Suo Wang, Feng Jian, Mingsheng Zhan

Published Mar 1, 2005• 23 citations
Publisher

Abstract

In this paper, we use the field entropy as a measurement of the degree of entanglement between the light field and the atoms of the system which is composed of two dipole–dipole interacting two-level atoms initially in an entangled state interacting with the single mode coherent field in a Kerr medium. The influence of the coupling constant of dipole–dipole interaction between atoms and the coupling strength of the Kerr medium with the light field and the intensity of the light field on the field entropy are discussed by numerical calculations. It is shown that when the coupling strength of the Kerr medium with the light field is large enough and the light field is strong, the degree of entanglement between the atoms with the light field becomes weaker. The degree of entanglement only changes slightly with the change of the coupling constant of dipole–dipole interaction between atoms.

DOI
10.1088/1009-1963/14/3/019

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In this paper, we use the field entropy as a measurement of the degree of entanglement between the light field and the atoms of the system which is composed of two dipole–dipole interacting two-level atoms initially in an entangled state interacting with the single mode coherent field in a Kerr medium. The influence of the coupling constant of dipole–dipole interaction between atoms and the coupling strength of the Kerr medium with the light field and the intensity of the light field on the field entropy are discussed by numerical calculations. It is shown that when the coupling strength of the Kerr medium with the light field is large enough and the light field is strong, the degree of entanglement between the atoms with the light field becomes weaker. The degree of entanglement only changes slightly with the change of the coupling constant of dipole–dipole interaction between atoms.
The field entropy can be regarded as a measurement of the degree of entanglement between the light field and the atoms of a system which is composed of two-level atoms initially in an entangled state interacting with the Schrödinger cat state. The influences of the strength of light field and the phase angle between the two coherent states on the field entropy are discussed by using numerical calculations. The result shows that when the strength of light field is large enough the field entropy is not zero and the degrees of entanglement between the atoms and the three different states of the light fields are equal. When the strength of the light field is small, the degree of entanglement is maximum in a system of the two entangled atoms interacting with an odd coherent state; it is intermediate for a system of the two entangled atoms interacting with the Yurke–Stoler coherent state and it is minimum in a system of the two entangled atoms interacting with an even coherent state.
According to the complete quantum theory,the quantum field-entropy evolution properties in a system of the two coupled two-level atoms interacting with a single-mode odd-coherent state light field are studied.Through numerical calculation the influence of the initial mean photon number n_0,the coupled intensity g of interaction between the single-mode field and atoms,and the coupled intensity g_a of dipole-dipole interaction between the two coupled atoms on the quantum field-entropy evolving while the initial state of the light field is a single-mode odd-coherent and the two coupled two-level atoms lay in different Einstein Poclolsky Rosen(EPR) entangled state respectively.The results indicate that the time evolving of quantum field-entropy is closely related to the initial atoms state.The quantum field-entropy evolution can display the phenomena of entanglement and disentanglement while they are periodically under the condition of intensity field(n_01). Meanwhile the phenomena of quantum interference is also discovered.The periodicity of the quantum field-entropy anomalous oscillation decreases gradually with the increasing of g values.When g_a is an especial constant,it is shown that the phenomena of period collapse-reversion can present.
We investigate the entanglement in a system of two coupling atoms interacting with a single-mode field by means of quantum information entropy theory. The quantum entanglement between the two atoms and the coherent field is discussed by using the quantum reduced entropy, and the entanglement between the two coupling atoms is also investigated by using the quantum relative entropy. In addition, the influences of the atomic dipole–dipole interaction intensity and the average photon number of the coherent field on the degree of the entanglement is examined. The results show that the evolution of the degree of entanglement between the two atoms and the field is just opposite to that of the degree of entanglement between the two atoms. And the properties of the quantum entanglement in the system rely on the atomic dipole–dipole interaction and the average photon number of the coherent field.
We have investigated the entanglement time evolution of two coupled two-level atoms in Kerr medium. Entanglement of the system is calculated by making use of concurrence. The influences of initial state, Kerr medium, and dipole-dipole coupling intensity between two atoms on the entanglement degree of the two atoms are revealed. Results show that the appropriate choice for the nonlinear coupling constant of Kerr medium and the dipole-dipole coupling intensity can improve the degree of atom-atom entanglement and eliminate the entanglement sudden death completely. We also find that invariant and stable entanglement occurs for a particular initial state.
In this paper,the field entropy evolution of two coupling atoms interacting with a single mode light field in Kerr medium is studied by means of the quantum theory.It has been shown that:the Kerr medium and the interaction of atoms will influence the periodicity of the evolution of the field entropy,make the connected degree between field and atoms weaken;the excited field intensity also influence the periodicity of the evolution of the field entropy,the connected degree between field and atoms is strengthened first and is weakened later when increases.
The atomic dipole squeezing effect in the system of two identical two-level atoms in the Bell state interacting with the two-mode entangled coherent state field in Kerr medium are investigated by means of solving the Schrdinger equation and numerical calculations. The effects on the atomic dipole squeezing effect produced by the atomic initial state, mean photon number of light field, the degree of the entanglement of the entangled coherent field, the coupling strength of the Kerr medium with the light field and the coupling strength of dipole-dipole interaction between atoms are discussed. The results show that the dipole squeezing effect does not appear for the Bell state |β11>, while there can be dipole squeezing effect under certain conditions for the Bell states |β00> or |β01> or |β10>. In the latter case, the dipole squeezing effect depends on the coupling strength of the Kerr medium with the light field, the mean photon number and the degree of entanglement of the two-mode entangled coherent field.