This paper studies entanglement between two dipole–dipole coupled atoms interacting with a thermal field via a two-photon process. It shows that the entanglement is dependent on the mean photon number of the thermal field and the dipole–dipole interaction. The results also show that the atom–atom entanglement through the two-photon process is larger than that through the one-photon process and a remarkable amount of entanglement between the atoms still remains at certain times even for a very highly noisy thermal field.

https://iopscience.iop.org/article/10.1088/1674-1056/17/6/032/pdf

The entanglement of two dipole–dipole coupled atoms interacting with a thermal field via a two-photon process

Following a recent proposal (Phys. Lett. A 346 (2005) 330) about quantum dense coding using a tripartite entangled GHZ state and W state, this paper proposes an experimentally feasible scheme for dense coding in cavity QED by using another peculiar tripartite entangled state. In the scheme the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field, the successful probability of dense coding scheme with this peculiar tripartite entangled state equals 1.

Quantum dense coding using a peculiar tripartite entangled state

In this paper, we have presented an analytic solution for two 2-level identical atoms interacting with a single-mode quantized radiation field, taking into account the level shifts produced by Stark shift. We assume that the two atoms are initially prepared in the exited state and the field in a coherent state. We investigate the purity loss of the system and bipartite partitions of the system. The effects of the Stark shift on the purity loss of the system and different bipartite partitions of the system (field-two atoms, atom-(field+atom)) through the tangles are considered. In particular, the effect of the Stark shift on the amount of entanglement between atoms and field is evaluated by the negativity.

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Entanglement and purity loss for the system of two 2-level atoms in the presence of the Stark shift

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 Schr?dinger 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.

Entropy evolvement properties in a system of Schrödinger cat state light field interacting with two entangled atoms

This paper investigates the entropy squeezing of a moving two-level atom interacting with the two-mode entangled coherent field via two-photon transition by using an entropic uncertainty relation and the degree of entanglement between the two-mode fields by using quantum relative entropy. The results obtained from numerical calculation indicate that the squeezed period, the duration of entropy squeezing and the maximal squeezing can be controlled by appropriately choosing the intensity of the light field, the atomic motion and the field-mode structure. The atomic motion leads to the periodic recovery of the initial maximal degree of entanglement between the two-mode fields. Moreover, there exists a corresponding relation between the time evolution properties of the atomic entropy squeezing and those of the entanglement between the two-mode fields.

https://iopscience.iop.org/article/10.1088/1674-1056/18/7/029/pdf

Quantum entanglement between the two-mode fields and atomic entropy squeezing in the system of a moving atom interacting with two-mode entangled coherent field

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.

王继锁

Papers

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