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Acta Physica Sinica

Dipole squeezing of atomic systems in dissipative environment

Mao-Fa Fang, Chang-Ning Pan, Zhao Xue-Hui, Diwu Yang

Published Jan 1, 2010• 2 citations
Publisher

Abstract

The atomic squeezing effect in the dissipative environment is investigated by means of the quantum theory of damping-density operator approach and numerical calculations. The effects on the atomic dipole squeezing effect produced by the atomic initial state and mean photon number of the thermal reservoir are discussed. The results show that the atomic dipole squeezing declines asymptotically to zero, and doesn’t disappear in finite time if the population rate in the excited state is higher than the ground state in the atomic initial state in the vacuum reservoir. However, the squeezing effect always disappears in the thermal reservoir, irrespective of the atomic initial state. With increase of mean photon of the thermal reservoir, the squeezing effect disappears faster.

DOI
10.7498/aps.59.6814

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The atomic squeezing effect in the dissipative environment is investigated by means of the quantum theory of damping-density operator approach and numerical calculations. The effects on the atomic dipole squeezing effect produced by the atomic initial state and mean photon number of the thermal reservoir are discussed. The results show that the atomic dipole squeezing declines asymptotically to zero, and doesn’t disappear in finite time if the population rate in the excited state is higher than the ground state in the atomic initial state in the vacuum reservoir. However, the squeezing effect always disappears in the thermal reservoir, irrespective of the atomic initial state. With increase of mean photon of the thermal reservoir, the squeezing effect disappears faster.
The atomic dipole squeezing effects in the system of a two-mode entangled states interacting with a Σ-type three-level atom were studied.We analyzed the effects of the degree of entanglement of the two-mode entangled coherent states,the ground state probability amplitude of atomic initial state,the detuning,and the mean photon numbers on the atomic dipole squeezing effects.The results indicate that the influence of the(degree) of entanglement of the two-mode entangled coherent states on the atomic dipole squeezing effects isn't noticeable.While the atomic initial state is in the ground state or excited state,the atomic dipole squeezing effects can not occur.While the probability of atomic initial state in ground state is equal to that in the excited state,the atomic dipole squeezing reaches its maximum.The enhancing of the detuning results in the increase of the frequency of atomic dipole squeezing.When the mean photon number of mode 1 remains unchanged and the mean photon number of mode 2 increases,the depth of atomic dipole squeezing decreases and the(frequency) of atomic dipole squeezing doesn't change.
This paper studied the atomic dipole amplitude squared squeezing in the system of a three level atom interacting with a single mode radiation vacuum field. Numerical method is adopted to discuss the influence of the relative value of atom field coupling constants and the atomic initial coherence on the squeezing effect. It is found that no squeezing is produced in the process of interaction if the atom is initially most excited or in its ground state. However, if the atom is initially in a coherent superposition state of the ground state and the most excited state, there will be dipole amplitude squared squeezing effect in the process of interaction; the squeezing degree depends on the phase factor relating to atomic initial coherence; when other conditions are fixed, the atom will produced optimum squeezing effect if the probability of atom initially in the most excited state is 1/4 and the probability of it initially in the ground state is 3/4. If none of the atom field coupling constants are zero, the quantities of squeezing vary periodically; the change period of the quantities of squeezing depends on the relative value of two atom field coupling constants.
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.
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Abstract In this paper we consider a system consisting of a number of two-level atoms in a Bose–Einstein condensate (BEC) and a single-mode quantized field, which interact with each other in the presence of two different damping sources, i.e. cavity and atomic reservoirs. The reservoirs which we consider here are thermal and squeezed vacuum ones corresponding to field and atom modes. Strictly speaking, by considering both types of reservoirs for each of the atom and field modes, we investigate the quantum dynamics of the interacting bosons in the system. Then, via solving the quantum Langevin equations for such a dissipative BEC system, we obtain analytical expressions for the time dependence of atomic population inversion, mean atom as well as photon number and quadrature squeezing in the field and atom modes. Our investigations demonstrate that for modeling the real physical systems, considering the dissipation effects is essential. Also, numerical calculations which are presented show that the atomic population inversion, the mean number of atoms in the BEC and the photons in the cavity possess damped oscillatory behavior due to the presence of reservoirs. In addition, non-classical squeezing effects in the field quadrature can be observed especially when squeezed vacuum reservoirs are taken into account. As an outstanding property of this model, we may refer to the fact that one can extract the atom–field coupling constant from the frequency of oscillations in the mentioned quantities such as atomic population inversion.