Photon distribution function for propagation of two-photon pulses in waveguide-qubit systems
O. O. Chumak, E. V. Stolyarov · Physical Review A · 2014
Propagation of a two-photon pulse in a waveguide coupled to a two-level system (TLS) is studied. The pulse is formed by two spatially separated identical wave packets. A set of equations governing the dynamics of the photon distribution in the configuration-momentum space is derived and solved. It is shown that the distribution function can be negative, which manifests its quasiprobability nature. A spectrum of the reflected light is found to be narrower than that of the transmitted light that features a pronounced filtering effect. Average numbers of the transmitted and reflected photons and their variances are shown to be dependent not only on the pulse widths and the light-TLS interaction but also on the pulse separation that can serve as an effective controlling parameter. Our approach is generalized for the case of an $n$-photon Fock state.