We investigate the single-photon transport properties in an optical waveguide coupled with a Λ-type three-level atom (ΛTLA) based on symmetric and asymmetric couplings between the photon and ΛTLA. The transmission and reflection coefficients of the single photon in such a hybrid system are deduced using the real-space approach. Symmetric and asymmetric bifrequency photon attenuators are realized by tuning the atom–photon couplings. The phase shift and group velocity delay of the transmitted single photon are also analyzed.
The spectral properties of an electromagnetically induced grating that is based on the spatial modulation of the Raman gain in the field of a standing pump wave in a three-level homogeneous medium have been discussed. It has been shown that, by varying the intensity or the frequency of the pump field, one can control the transmission and reflection spectra, while the transmission and reflection coefficients of the probe (Raman) wave can simultaneously be greater than unity. The influence of the nonideality of the standing wave on the spectral characteristics of the grating has been studied.
We study scattering for continuous-time quantum walks on finite graphs with two attached leads. We derive explicit formulae for the two-terminal scattering matrix in terms of characteristic polynomials of the finite graph and its vertex-deleted subgraphs. For real-weighted two-terminal graphs, we then introduce three real quantities,
μ1,
μ2, and
ν, which are each additive under parallel composition of graphs. In these variables, perfect transmission at fixed momentum is characterized by the condition
μ1=μ2 together with a hyperbola in the corresponding
(μ,ν)-plane, whose points determine the transmission phase. This turns the search for graphs with prescribed transmission properties into a geometric vector-sum problem for smaller building blocks.