A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed.Compared with that generated in a general fourlevel system,the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption.By using the numerical results,we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.
First we present a theoretical analysis of classical noise in ghost imaging system based on the coherent-mode representation theory. The classical noise depends crucially on the distribution of the eigenvalues of the coherent-mode representation of the source and the decomposition coefficients of the object imaged. We show that both decreasing the distribution of the decomposition coefficients and increasing the distribution of the eigenvalues can lead to the decrease of classical noise.
We study the spatial behavior of a deflected beam in a coherent A-type three-level atomic medium with an inhomogeneous control laser.When the Rabi coupling by the control laser is in a Gaussian profile,the spatialdependent refraction index of the atomic medium will result in a beam splitting as well as the deflection of the slow probe light under electromagnetically induced transparency.In terms of the phase difference between the two splitting beams and the position of the splitting,the possible interpretation of the splitting is given in theory.
When semiconductor quantum wells(SQWs) interact with lasers,the group velocity of the low-intensity light pulse is studied theoretically.It is shown that by adjusting the parameters,slow light propagation of the probe field can be exhibited in such a system.Meanwhile,the probe absorption-gain spectra can be changed from absorption to zero,i.e.,electromagnetically induced transparency(EIT).It is easy to observe the light propagation experimentally,and it leads to potential applications in many fields of solid-state quantum information,for example,optical switching,detection and quantum computing.
