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Journal of Qinghai Normal University

Steady-State Population of a Moving Ladder-Type Three-Level Atom in Broad-Band Squeezed Vacuum

Yuan Hai-liang

Published Jan 1, 2006• 0 citations
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Abstract

This paper mainly deals with the steady-state population of a moving ladder-type three-level atom,driven by a superposition of a monochromatic laser wave with a broad-band squeezed vacuum,From the Hamiltonian of the atomic system,making use of Born-Markoff approximation,we derive the master equation for the system and the atomic Bloch equations and obtain the steady-state solutions of the optical Bloch equations using numerical calculation.Then we discuss the dependence of the attained population σ_(ii) on parameters such as detuning Δ,Rabi frequencies e_1e_2,phase ,squeezing photon number N and spontaneous decay ratesγ_1 γ_2 etc in different cases by using graphical method.

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Radiation Pressure of a Moving Ladder-Type Three-Level Atom in Broad-Band Squeezed Vacuum

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This paper mainly studies the radiation pressure of a moving ladder-type three-level atom driven by a superposition of a bichromatic laser wave with a broad-band squeezed vaccum and obtains the steady-state expression for the radiation force.Frist,from the master equations for a moving ladder-type three-level atom driven by a superposition of a bichromatic laser wave with a broad-band squeezed vaccum,we derive the equations for the atomic density matrix element.Second,by choosing proper scaled variables,Bloch equations for the atomic population are obtained.Then,from Heisenberg equation for atomic momentum,considering the adiabatic approximation,the mathematical expression of the mean radiation pressure is obtained.At last,by considering the steady-state case in which the atomic population doesn't vary with time and the condition,the steady-state expression of the radiation pressure is obtained.

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Journal of the Physical Society of Japan•Aug 15, 1998•0 citations

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By analyzing the influence of the motion of the atoms on the steady-state populations of the atomic levels,we found that the Doppler frequency shift in the double-photon resonance occurs near to the zero double-photon detuning and the Doppler frequency shift in the single-photon resonauce near to the zero single-photon detuning.The double-photon resonance near to zero double-photon detuning does not make the Doppler frequency shift occured when atoms are driven by two counter propagating but same frequency laser beams.

Journal of Qinghai University•Jan 1, 2007•0 citations

Effect of a Squeezed Vacuum on Coherent Population Trapping in a Three-level Lambda System

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Master equation methods are used to investigate the effects of a broad-band squeezed vacuum on a three-level atom of the lambda configuration. The two-mode squeezed vacuum is treated as a Markovian reservoir in a non-stationary phase-dependent state. In addition to the squeezed vacuum the atom is driven by two coherent laser fields each of which, depending on the polarization, can couple to one or both of the atomic transitions. We show that in general the optical Bloch equations for the atomic density matrix elements have oscillatory coefficients, thereby necessitating the use of Floquet methods. For the case of equal laser frequencies, which are also equal to the carrier frequency of the squeezed vacuum, the coefficients of the Bloch equations become time independent and stationary solutions for the populations and coherences are obtained by standard matrix methods. For the ordinary vacuum the usual coherent population trapping effect at two-photon resonance is obtained, with the upper state population being zero. An unsqueezed thermal field partially destroys the trapping effect as the upper state population is no longer zero at two-photon resonance. The squeezed vacuum has the effect of improving the trapping in that the coherence hole becomes more pronounced for some values of the relative phase between the squeezed vacuum and the driving fields. The additional effects of a coherence transfer rate between the two optical coherences, which occurs for special choices of angular momentum quantum numbers are also studied. For the case of equal laser frequencies, the inclusion of this coherence transfer process destroys population trapping and reduces the lambda system to a two-level system. However, for the case of unequal laser frequencies, the coherence transfer process in combination with the squeezed vacuum can restore to some extent the population trapping. We show that other features that do not occur for two-level atoms, such as stationary population inversions between pairs of the atomic levels, also depend on the relative phase and can be enhanced in the squeezed vacuum. In the case of unequal frequencies of the driving fields the population in the upper state depends on the relative phase only when the carrier frequency of the squeezed vacuum is equal to one of the two frequencies of the driving fields. When the carrier frequency of the squeezed vacuum is slightly detuned from both frequencies of the driving fields, the population in the upper state is insensitive to the relative phase but is dependent on the degree of squeezing. For large detunings, the population does not show any dependence on the degree of squeezing and its distribution in function of the two-photon detuning is similar to that in the thermal vacuum field.

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Laser Cooling, Friction and Diffusion in Three-Level Cascade System in Squeezed Vacuum

Lei Tan, Cuiling Zhang, Jinfang Zhang +2 more

A theoretical study is carried out for the laser cooling of a moving three-level atom in a ladder configuration, driven by a bichromatic laser fields with a broad-band squeezed vacuum. The friction, diffusion coefficients and the equilibrium temperature are calculated numerically and shown graphically as a function of two-photon detunings for various cases of the squeezed vacuum. It is shown that the relative phases between the two coherent fields and the squeezed vacuum field play an important role in the cooling process. For a suitable choice of parameters, the atomic cooling temperature may be reduced to below that in the case of a vacuum, even down to two orders below the Doppler temperature limit. The efficiency of this cooling scheme is also analyzed.

Journal of the Physical Society of Japan•Sep 11, 2006•0 citations
This paper mainly deals with the steady-state population of a moving ladder-type three-level atom,driven by a superposition of a monochromatic laser wave with a broad-band squeezed vacuum,From the Hamiltonian of the atomic system,making use of Born-Markoff approximation,we derive the master equation for the system and the atomic Bloch equations and obtain the steady-state solutions of the optical Bloch equations using numerical calculation.Then we discuss the dependence of the attained population σ_(ii) on parameters such as detuning Δ,Rabi frequencies e_1e_2,phase ,squeezing photon number N and spontaneous decay ratesγ_1 γ_2 etc in different cases by using graphical method.
This paper mainly studies the radiation pressure of a moving ladder-type three-level atom driven by a superposition of a bichromatic laser wave with a broad-band squeezed vaccum and obtains the steady-state expression for the radiation force.Frist,from the master equations for a moving ladder-type three-level atom driven by a superposition of a bichromatic laser wave with a broad-band squeezed vaccum,we derive the equations for the atomic density matrix element.Second,by choosing proper scaled variables,Bloch equations for the atomic population are obtained.Then,from Heisenberg equation for atomic momentum,considering the adiabatic approximation,the mathematical expression of the mean radiation pressure is obtained.At last,by considering the steady-state case in which the atomic population doesn't vary with time and the condition,the steady-state expression of the radiation pressure is obtained.
A study is made of the steady state populations of a three level ladder atom in a squeezed vacuum, driven by a superposition of a monochromatic laser wave with incoherent population pumping. Using the density matrix equations for the system, the steady state populations are calculated numerically and shown graphically as functions of two photon detuning for various cases of the squeezed vacuum and different incoherent pump rates. It is shown that the incoherent population pumping tends to greatly decrease the two photon absorption from the squeezed vacuum.
A three-level ladder atom driven by two coherent laser fields with rather different frequencies in various kinds of reservoirs is considered. Making use of the master equation and Bloch equation, we calculate numerically and show graphically the steady-state populations versus two-photon detuning. We also discuss and compare the two-photon and one-photon processes occurring for various cases. For a squeezed vacuum, only when the carrier frequency of the squeezed vacuum equals the average of frequencies of the two driving fields and the phase matching condition is fulfilled, will there be a strong two-photon resonant absorption from the squeezed vacuum, a characteristic different from absorption of photons from a classical field; Otherwise, the two-photon ab-sorption rate from the squeezed vacuum will be greatly diminished.
By analyzing the influence of the motion of the atoms on the steady-state populations of the atomic levels,we found that the Doppler frequency shift in the double-photon resonance occurs near to the zero double-photon detuning and the Doppler frequency shift in the single-photon resonauce near to the zero single-photon detuning.The double-photon resonance near to zero double-photon detuning does not make the Doppler frequency shift occured when atoms are driven by two counter propagating but same frequency laser beams.
Master equation methods are used to investigate the effects of a broad-band squeezed vacuum on a three-level atom of the lambda configuration. The two-mode squeezed vacuum is treated as a Markovian reservoir in a non-stationary phase-dependent state. In addition to the squeezed vacuum the atom is driven by two coherent laser fields each of which, depending on the polarization, can couple to one or both of the atomic transitions. We show that in general the optical Bloch equations for the atomic density matrix elements have oscillatory coefficients, thereby necessitating the use of Floquet methods. For the case of equal laser frequencies, which are also equal to the carrier frequency of the squeezed vacuum, the coefficients of the Bloch equations become time independent and stationary solutions for the populations and coherences are obtained by standard matrix methods. For the ordinary vacuum the usual coherent population trapping effect at two-photon resonance is obtained, with the upper state population being zero. An unsqueezed thermal field partially destroys the trapping effect as the upper state population is no longer zero at two-photon resonance. The squeezed vacuum has the effect of improving the trapping in that the coherence hole becomes more pronounced for some values of the relative phase between the squeezed vacuum and the driving fields. The additional effects of a coherence transfer rate between the two optical coherences, which occurs for special choices of angular momentum quantum numbers are also studied. For the case of equal laser frequencies, the inclusion of this coherence transfer process destroys population trapping and reduces the lambda system to a two-level system. However, for the case of unequal laser frequencies, the coherence transfer process in combination with the squeezed vacuum can restore to some extent the population trapping. We show that other features that do not occur for two-level atoms, such as stationary population inversions between pairs of the atomic levels, also depend on the relative phase and can be enhanced in the squeezed vacuum. In the case of unequal frequencies of the driving fields the population in the upper state depends on the relative phase only when the carrier frequency of the squeezed vacuum is equal to one of the two frequencies of the driving fields. When the carrier frequency of the squeezed vacuum is slightly detuned from both frequencies of the driving fields, the population in the upper state is insensitive to the relative phase but is dependent on the degree of squeezing. For large detunings, the population does not show any dependence on the degree of squeezing and its distribution in function of the two-photon detuning is similar to that in the thermal vacuum field.
A theoretical study is carried out for the laser cooling of a moving three-level atom in a ladder configuration, driven by a bichromatic laser fields with a broad-band squeezed vacuum. The friction, diffusion coefficients and the equilibrium temperature are calculated numerically and shown graphically as a function of two-photon detunings for various cases of the squeezed vacuum. It is shown that the relative phases between the two coherent fields and the squeezed vacuum field play an important role in the cooling process. For a suitable choice of parameters, the atomic cooling temperature may be reduced to below that in the case of a vacuum, even down to two orders below the Doppler temperature limit. The efficiency of this cooling scheme is also analyzed.