Single Two-Level Atom

Zeng Ke, Mao-Fa Fang

The entanglement properties of the system of two two-level atoms interacting with a single-mode vacuum field are explored. The quantum entanglement between two two-level atoms and a single-mode vacuum field is investigated by using the quantum reduced entropy; the quantum entanglement between two two-level atoms and that between a single two-level atom and a single-mode vacuum field are studied in terms of the quantum relative entropy. The influences of the atomic dipole–dipole interaction on the quantum entanglement of the system are also discussed. Our results show that three entangled states of two atoms–field, atom–atom and atom–field can be prepared via two two-level atoms interacting with a single-mode vacuum field.

Dieter Suter

Alberto Barchielli, Matteo Gregoratti

V. I. Koroli

The interaction between the pair of cold two-level atoms and the single-mode cavity field is investigated. The two-level atoms in the pair are supposed to be indistinguishable. This problem generalizes the two-photon Jaynes-Cummings model of a single two-level atom interacting with the squeezed vacuum. The model of the pair of indistinguishable two-level atoms is equivalent to the problem of the equidistant three-level radiator with equal dipole moment matrix transition elements between the adjacent energy levels. Supposing that at the initial moment the field is in the squeezed vacuum state we obtain the exact analytical solution for the atom-field state-vector. By using this solution the quantum-statistical and squeezing properties of the radiation field are investigated. The obtained results are compared with those for the single two-level atom system. We observe that in the model of the pair of cold two-level atoms the exact periodicity of the squeezing revivals is violated by the analogy with the single two-level atom one.

V. I. Koroli, Victor V. Zalamai

We study the interaction between a laser-cooled and trapped equidistant three-level atom (ion) and a single-mode cavity field. The dipole moment matrix transition elements between the adjacent atomic energy levels d 12 and d 23 are assumed to be different. This problem generalizes the model of a pair of indistinguishable two-level atoms. An intensity-dependent coupling is assumed between the three-level atom and the radiation field. In this situation, we suppose that at the initial moment the field is in the Holstein–Primakoff SU (1,1) coherent state and obtain the exact analytical solution for the atom–field state vector. The quantum-statistical and squeezing properties of the radiation field are investigated. The obtained results are compared with those for the single two-level atom model. We observe that the exact periodicity of the squeezing revivals that was observed in the case of the single two-level atom is violated in the model involving the equidistant three-level radiator with different dipole moment matrix transition elements. In other words, the exact periodicity of the physical quantities can be destroyed only when more than two levels of the single-atom model are taken into account. Two limiting cases are considered. In the first case, when d 12 → d 23 , the quantum-statistical and squeezing properties of the single-mode cavity field are similar to those for a pair of indistinguishable two-level atoms. In the second case, when d 12 → 0, the exact periodicity of the squeezing revivals takes place. This limiting case is equivalent to the single two-level atom model.