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Chinese Physics

Entanglement properties in a system of a pairwise entangled state

Tang-Kun Liu, Cheng Wei-Wen, Shan Chuan-Jia, Gao Yun-feng, Ji‐Suo Wang

Published Dec 1, 2007• 8 citations
Publisher

Abstract

Based on the quantum information theory, this paper has investigated the entanglement properties of a system which is composed of the two entangled two-level atoms interacting with the two-mode entangled coherent fields. The influences of the strength of light field and the two parameters of entanglement between the two-mode fields on the field entropy and on the negative eigenvalues of partial transposition of density matrix are discussed by using numerical calculations. The result shows that the entanglement properties in a system of a pairwise entangled states can be controlled by appropriately choosing the two parameters of entanglement between the two-mode entangled coherent fields and the strength of two light fields respectively.

DOI
10.1088/1009-1963/16/12/024

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Based on the quantum information theory, this paper has investigated the entanglement properties of a system which is composed of the two entangled two-level atoms interacting with the two-mode entangled coherent fields. The influences of the strength of light field and the two parameters of entanglement between the two-mode fields on the field entropy and on the negative eigenvalues of partial transposition of density matrix are discussed by using numerical calculations. The result shows that the entanglement properties in a system of a pairwise entangled states can be controlled by appropriately choosing the two parameters of entanglement between the two-mode entangled coherent fields and the strength of two light fields respectively.
We investigate the entanglement properties of the two-mode coherent fields interacting with a two-level atom via the two-photon transition. We discuss the quantum entanglement between the two-mode coherent fields and the two-level atom by using the quantum reduced entropy and that between the two-mode coherent fields by using the quantum relative entropy. We also examine the influences of the initial states of the atom and the two-mode coherent fields on the quantum entanglement of the system. Our results show that three types of entangled states can be prepared via the two-mode coherent fields interacting with a two-level atom and choosing appropriately the initial-state parameters of the system.
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.
In this article,the time evolution properties of the field entropy in the system of the two identical two-level entangled atoms interacting with the single-mode coherent light field are studied by means of full quantum theory.The influences of the initial states and the degree of entanglement of two identical two-level entangled atoms and the intensity of the light field on the field entropy are discussed by numerical calculations.The results show that the average value and the oscillation frequency of the field entropy increases with the increasing of the mean photon number,the oscillation of the field entropy presents stated periods in the weak light field and presents collapses and revivals in the increased light field,the amplitudes of field entropy increase with increasing initial degree of entanglement of two entangled atoms.
We studied the entanglement properties of the system consisting of two atoms in Bell states interacting with the two-mode odd-even entangled coherent field by utilizing the complete quantum theory. The influences of the initial Bell state of the atoms, the intensity of field, the coupling strength of interaction between atoms and the initial degree of the entanglement between the two-mode fields on the atomic entropy and on negativity are discussed by using numerical calculations. It turns out that the two atoms can keep their initial maximal entangled state while the two-atom and the two-mode field keep their initial disentangled state if the two atoms are initially in |β11〉. Therefore, for the initial atomic state |β00〉 or |β01〉, the increasing of the field intensity can be a help to prepare the atom-field entanglement, and for |β10〉, it is beneficial for the atom–atom entanglement. Meanwhile, for the initial atomic state |β10〉 and |β01〉, strong coupling strength of interaction between atoms is beneficial for the atom–atom entanglement, but for |β00〉, it can be helpful for the atom-field entanglement.
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.
By means of the quantum theory and numerical calculations method,the entanglement time evolution of the two identical two-level atoms in Bell states interacting with the two-mode odd-even entangled coherent field is investigated by using Negativity.The effects of the atoms initial state,mean photon numbers of field,the degree of the entanglement for the entangled coherent fields,and the coupling strength of interaction between atoms on the Negativity are discussed.The results show that the two-atom entanglement state will forever stay in the maximum entangled state when the initial state is |β_(11)〉,while the Bell state |β_(00)〉atoms appear disentanglement most of the scaled time.For the state |β_(10)〉,mean photon numbers of field can be a great help,and in the state |β_(01)〉the coupling strength of interaction between atoms plays a major role in the two-atom entanglement.