It is shown theoretically that additional illumination by a squeezed field of a thin layer of two-level atoms, which interact with a resonant coherent electromagnetic wave, results in bistable transmission/reflection of this wave. This bistability depends strongly on the difference between the phases of the coherent and squeezed fields.
We investigate the problem of resonant re flection and transmission of an ultrashort light pulse passing through a medium consisting of two-level atoms. We show that for a thin layer it is important to take into account the difference between the external macroscopic field and the field acting on the individual atoms within the medium. The local field correction leads to an inversion dependent resonant frequency. In thin layers this generates a new mechanism of nonlinear transparency induced by the dynamical frequency shift. When the excitation frequency is larger than the original resonant frequency, then the transmission of the layer exhibits bistable behavior.
We discuss the optical bistable behavior of a system of N two-level atoms pumped by a coherent input field and coupled to a squeezed vacuum field by treating the optical bistability of such a system as an input-output problem. We consider the equation of motion for atomic dipole moments, coupled to the cavity field and the squeezed vacuum, and the boundary condition connecting the input and output fields with the atomic lowering operator. A simple analytical expression for the influence of the squeezed vacuum input on the bistable behavior of the output field is derived by this method. The results indicate a strong influence of the squeezed vacuum input on optical bistability. The squeezed (stretched) vacuum input field tends to increase (decrease) the range of optical bistability.
We use a fully quantum, many-body treatment to show mirrorless optical bistability in terms of the spacial properties of interacting two-level systems. The bistability effects are related to the coherent dipole-dipole interactions which introduce an inversion-dependent renormalization of the frequency (or relaxation). Conditions of stability and instability are discussed for a thin sample of two-level atoms with a width smaller than a wavelength. For a long sample of two-level atoms, we find that the two phases of high transmissivity and low transmissivity may coexist spacially in the material.