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Acta Physica Sinica

Influence of the field with varying frequency modulation on atomic population inversion in non-ratating-wave approximation

Liao Xu, Cong Hong-Lu, Jiang Dao-Lai, Xuezao Ren

Published Jan 1, 2010• 2 citations
Publisher

Abstract

By the method of coherent-state orthogonalization expansion, the evolution of atomic population inversion is investigated in the non-rotating-wave approximation. The numerical results indicate that, when field frequency and coupling do not change with time, the collapse-revival period of population inversion increases with the mean photon number of the field increasing, and the quick oscillation due to virtual photon process increases with couplings strengthening. When the frequency changes with time in the sine form, amplitude α and angle frequency β of the field both have a great influence on atomic population inversion. The sudden jumping of the field frequency can lead to some new collapses and rebibals in the evolution of atomic population inversion. Both of the field frequency forms can have an influence on quick oscillation due to virtual photon process.

DOI
10.7498/aps.59.5508

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By the method of coherent-state orthogonalization expansion, the evolution of atomic population inversion is investigated in the non-rotating-wave approximation. The numerical results indicate that, when field frequency and coupling do not change with time, the collapse-revival period of population inversion increases with the mean photon number of the field increasing, and the quick oscillation due to virtual photon process increases with couplings strengthening. When the frequency changes with time in the sine form, amplitude α and angle frequency β of the field both have a great influence on atomic population inversion. The sudden jumping of the field frequency can lead to some new collapses and rebibals in the evolution of atomic population inversion. Both of the field frequency forms can have an influence on quick oscillation due to virtual photon process.
The interactions between a two-level atom and a coherent field with a time-varying frequency without rotating-wave approximation have been investigated. The typical cases of the frequency of the field varying with time in the sine and rectangle forms have been considered. It is found that the collapse-revival phenomena and quick oscillations due to virtual photon processes of the atomic population inversion are deformed as the frequency changes with time in the sine form. The rectangular frequency modulation can lead to some new collapses and revivals in the evolution of the atomic population inversion. The sudden jumping of the field frequency can also lead to the sudden change of the quick oscillations due to virtual photon processes.
The interactions between a two-level atom and a squeezed field of time-varying frequency have been investigated. The properties of the atomic population inversion for two typical cases——the frequency of the field varying with time in the forms of sine function and rectangular pulses——have been considered. For the frequency changing with time in sinusoidal form, the collapse-revival phenomenon of the atomic population inversion is deformed not only by the frequency-modulation but also by the squeeze coefficient and the squeeze phase of the field. The sudden jumping of the field with rectangular pulsed frequency-modulation can lead to new collapses and revivals in the evolution of the atomic population inversion. The rectangular pulsed frequency-modulation can also lead to small-amplitude fast oscillations of the atomic population inversion during the pulse. There is no relation between the latter phenomena and the squeeze coefficient of the field.
In this paper,the atomic population evolution vs.time in the system of three-level casade atom interacting with a single-mode coherent light field is investigated without rotating wave approximation.The influence of the initial mean photon number n of field,of the atom-field coupling sonstant λ and of the light frequency ω on the atomic population is also discussed.And we compare without rotating wave approximation with rotating wave approximation,and find many differences of the atomic population evolution curves on the identical initial field-strength.It has been shown that because of the influence of the virtual-photon process,the little saw-tooth which represents the quantum noise of the system appear in the evolution curves of thae atomic population of the stimulated radiation field.With the increase of light frequency ω,the quantum noise of the system decreases,and then disappears.And with the increases of the initial field-strength n,the quantum noise of the system increases gradually.Meanwhile,the initial field-strength n and atom-field coupling constant λ influence the oscillation period the quantum collapse-revival of the atomic population evolution curves of stimulated radiation field,too.
The interactions between a two-level atom and a field via two-photon transition without rotating wave approximation have been investigated. We emphasize the dynamic behaviors of the atomic population inversion, the field squeezing, and the atomic dipole squeezing numerically when the field frequency varies with time in the forms of sine and rectangle. Some interesting phenomena are discovered and discussed. The good periodic character of the atomic population inversion in the standard two-photon Jaynes–Cummings model is weakened by the influence of the sine field frequency modulation. The rectangular field frequency modulation can change the correlation among different oscillations suddenly and induce new collapse-revival processes of the atomic population inversion. The field squeezing increases at the beginning of time, but then decreases and loses as the time increases after it reaches the maximum due to the sine modulation. The effects of the rectangular modulation on the field squeezing depend mostly on the appearance time of the modulation. The atomic dipole squeezing is weakened under the influence of the sine or rectangular modulation. Our results indicate that it is possible to perform the dynamic controlling of the system properties by changing the parameters of the system with time. This implies that one can dynamically control a quantum information process by choosing the system modulation properly.
The interactions between a two-level atom and a coherent field with a time-varying frequency have been investigated. The two typical cases---the frequency of the field varying with time in the forms of sine and rectangle---have been considered. It is found that the collapse-revival phenomena of the atomic population inversion are deformed as the frequency changing with time in sine form and the rectangular frequency modulation can lead to some new collapses and new revivals in the evolution of the atomic population inversion.
The two-photon transition for a two-level atom interacting with a single-mold electromagnetic field has been investigated. The initial coherent states with time-varying frequency are considered. The effects of the frequency modulation in sinusoidal form on the atomic population inversion and the squeezing properties of the atom and field are studied. The frequency change can lead the collapse-revival period of population inversion to increase, the maximum value of the revival to decrease, and the squeezing effects of the field and atom are weakened.