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Journal of Applied Optics

Effect of modulated amplitude on oscillation of population probability

FU Zhen-xing

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

To explore the physical mechanism induced by a frequency-modulated light field,the phenomenon of the oscillation of population probability in a two-level system under a frequency-modulated field is analyzed theoretically by means of the density matrix equation and Bloch vector model.The effect of the modulated amplitude on the process of the oscillation is also discussed.The results show that the oscillation of population probability and population transfer is modulated by the modulated amplitude.Increasing the modulated amplitude when the other parameters are fixed,the oscillation of population probability is weakened,and the efficiency of population transfer and the absorption are enhanced.The analysis in Bloch vector model shows that the population oscillation reflects the dynamic transformation process among the population transfer,absorption and polarization in the quantum system.

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To explore the physical mechanism induced by a frequency-modulated light field,the phenomenon of the oscillation of population probability in a two-level system under a frequency-modulated field is analyzed theoretically by means of the density matrix equation and Bloch vector model.The effect of the modulated amplitude on the process of the oscillation is also discussed.The results show that the oscillation of population probability and population transfer is modulated by the modulated amplitude.Increasing the modulated amplitude when the other parameters are fixed,the oscillation of population probability is weakened,and the efficiency of population transfer and the absorption are enhanced.The analysis in Bloch vector model shows that the population oscillation reflects the dynamic transformation process among the population transfer,absorption and polarization in the quantum system.
The temporal evolution of atomic transition in a two-state system under the frequency-modulated field and its dynamic evolution are discussed by means of the density matrix equation and the method of Bloch vector model respectively. The results show that the oscillation of population probability appears in time domain under the effects of frequency -modulated pulse.The dynamic evolution of the Bloch vector indicates that the oscillation of population probability reflects the physical converted process among the population transfer,dispersion and absorption in the two-level system.
The time evolution of population probability in two-level system under a linear frequency-chirped field is studied by mean of the density matrix equation of motion when the decay of the excited state is considered,and the physical mechanism of the oscillation in the process of the population transfer is analyzed using the dynamic evolution process of the Bloch vector under the picture of Bloch vector model.The result shows that the phenomenon of oscillation in the two-level system reveals the dynamic conversion transfer among population transfer,dispersion and absorption.
The temporal evolution of atomic transition in a two-level system under the frequency-chirped pulse field and its dynamic analysis are discussed respectively by means of the density matrix equation and the method of Bloch vector model.The result shows that the population probability oscillates in time domain under the effects of frequency-chirped pulse.The dynamic evolution process of the Bloch vector indicates that the oscillation of the population probability reflects the physical transformation process among the population transfer,dispersion and absorption in the system.
To explore the physical mechanism and the essence of the quantum diffraction in time-domain, the wave functiondiffraction in time-domain of a two-level system under the pulse field with a chirped frequency is investigated by means of thedensity matrix equation and the Bloch vector model. The modulations of the quantum diffraction by the chirped factors are discussed.The dynamic evolution process of the population transfer and the effect of the quantum diffraction with different chirped factors areanalyzed. The interaction mechanism and the physical process can found a clear description in the Bloch vector picture.
We propose a technique for coherent population inversion of a two-state system, which uses an amplitude-modulated pulse. In the modulation-free adiabatic basis, the modulation introduces oscillating interaction between the adiabatic states. In a second rotating-wave approximation picture, this oscillating interaction induces a pair of level crossings between the energies of the adiabatic states if the modulation frequency is chosen appropriately. By suitably offsetting the modulation with respect to the center of the pulse, one can make the modulation act only in the vicinity of one of these crossings. In a higher-order adiabatic basis, this crossing shows up as an avoided crossing between the energies of the higher-order adiabatic states. As a result robust and efficient population transfer can be achieved between the adiabatic states, and hence, between the original bare states. We derive analytically the conditions on the interaction parameters for this technique and verify them with numerical simulations. Possible experimental implementations are discussed.
Using the multiphoton Jaynes-Cummings model,the squeezing effect of the field in the system of a two-level atom interacting with the single mode coherent field through mutiphoton transition was studied.The frequency of the field varying with time in the form of sine was considered.The influences of amplitude and angular frequency of the field-frequency variation on squeezing effects of the field were discussed by numerical calculations.The influences of mean photon number of the field on squeezing effects of the field were also discussed.Calculation results indicate that the squeezing effects of field strengthens with the increase of the amplitude u of field-frequency variation and weaken with the increase of mean photon number of the field.The time-evolution behavior of quadrature squeezing function Q1 is modulated by the field-frequency variation.The modulation intensity is enchanced with the increase of the amplitude u of field-frequency variation,and when the amplitude u of field-frequency variation is larger than a fixed value,the time-evolution of quadrature squeezing function Q1 will display quasi-periodicity oscillation behavior.Its oscillation frequency agrees with the angular frequency of field-frequency variation.