Phase-Controlled Transparent Superluminal Light Propagation in a Doppler-Broadened Four-Level N-Type System

Abstract

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.

Phase-controlled photon drag in a slow-light moving medium

“…It is well known that the optical properties of a closedloop atomic system interacting with laser fields are completely phase-dependent [29][30][31][32]. The phase-dependent behaviour can be also induced by quantum interference due to spontaneous emission of an atom with two closely lying levels [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Such coherence can be created by the interference of spontaneous emission, called spontaneously generated coherence (SGC), of either a single excited level to two close-lying atomic levels [34] or two close-lying atomic levels to a common atomic level [35].…”

Maximal atom-photon entanglement in an N-type atomic system

“…On the other hand, the optical properties of a four-level N-type quantum system have been extensively studied [37][38][39][40][41][42]. For instance, resonance fluorescence, squeezing and absorption spectra of a laser-driven N-type system was investigated and it was demonstrated that quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep [39].…”

“…For instance, resonance fluorescence, squeezing and absorption spectra of a laser-driven N-type system was investigated and it was demonstrated that quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep [39]. Propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence (SGC) was theoretically investigated and found that group velocity of light pulse can be controlled by relative phase of applied fields [42]. Though the above-mentioned effects have been studied in the system, only a few studies have been performed on its quantum entangled properties and to the best of our knowledge, the maximal atom-photon entanglement in such system have not been achieved previously.…”