The effect of a coupling laser field on the entanglement of a threelevel quantum system and its spontaneous emission is investigated via reduced quantum entropy. We consider two schemes, the upper-and lower-level couplings. By calculating the degree of entanglement (DEM) for both systems, it is shown that the entanglement between atom and its spontaneous emission can be controlled by the coupling laser field. This field, however, affects the entanglement differently in the two schemes; it is only the lower-level coupling scheme that shows a nonzero steady state DEM which can be controlled by the intensity and detuning of the coupling laser field.
Abstract. The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence (SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self-and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature, the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.
This paper presents a novel Gait Pattern Generator (GPG) developed for the \Alice" social humanoid robot, which up to now lacked an appropriate walking pattern. Due to the limitations of this robot, the proposed gate pattern generator was formulated based on a nine-mass model to decrease the modeling errors and the inverse kinematics of the whole lower-body was solved in such a way that the robot remained statically stable during the movements. The main challenge of this work was to solve the inverse kinematics of a 7-link chain with 12 degrees of freedom. For this purpose, a new graphical-numerical technique has been provided using the de nition of the kinematic equations of the robot joints' Cartesian coordinates. This method resulted in a signi cant increase in the solution rate of calculations. Finally, a novel algorithm was developed for step-by-step displacement of the robot towards a desired destination in a two-dimensional space. Performance of the proposed gate pattern generator was evaluated both with a model of the robot in a MATLAB Simulink environment and in real experiments with the Alice humanoid robot.
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