Considers a system of N coherently driven two-level atoms contained in a volume with dimensions much smaller than a wavelength. The atoms may decay by a completely cooperative mechanism which conserves (J 2 ), alternatively they may decay by a mechanism which fails to conserve (J 2 ). The steady-state behaviour in each case is determined using the single-atom solutions together with two limiting approximations: (a) complete atomic correlation, (b) no atomic correlation. In case (a) a behaviour characteristic of a second-order phase transition is obtained while in case (b) a first-order phase transition results.
In this paper the dynamics of wave fields in a cavity with one sinusoidally moving mirror are investigated. The wave equation is solved approximately using the method of multiple time scales. Frequency shifts as well as amplitude and phase modulations of cavity modes are given. In all cases when it is possible, an approximate effective field Hamiltonian operator is derived. In the adiabatic case it is then used to analyze the interaction of radiation with a two-level atom passing through the cavity. Corrections to the Rabi oscillations due to the time-dependent frequency of the cavity photons are investigated. It is shown that adiabatic motion of a mirror can lead to suppression of the Rabi oscillations of atomic inversion.
We discuss a mean-field quantum-mechanical model which describes the dynamics of a homogeneously broadened system of two-level atoms contained in a pencil-shaped resonant cavity and driven by a coherent resonant field
EI. The model is treated in the semiclassical approximation. The model is justified on the basis of Maxwell-Bloch equations with two coherently coupled directions of propagation, with boundary conditions for the fields taken into account. Above a suitable critical density of atoms the system exhibits a bistable behavior including both the stationary situation and the transient, both the light transmitted in the forward direction and the fluorescent light. Bistability is shown to be a consequence of atomic cooperation. We give a simple description of optical bistability leading to new predictions for the transient behavior of the transmitted light and for the spectrum of the fluorescent light. The damping constant which characterizes the rate of appraoch to the stationary situation exhibits a hysteresis cycle. In the low-transmission regime the approach is monotonic, whereas in the highly transmitting situation the approach is oscillatory. One finds a critical slowing down in correspondence with the values
EI(+), ${{E}_{I}}^{(\ensuremath{-})}$ of the incident field where the transmitted field (as well as the total fluorescence intensity, the rate of approach to the stationary state, etc.) changes discontinuously. On the basis of the regression hypothesis we give a qualitative description of the spectrum of the fluorescent light. This is shown to undergo hysteresis and discontinuous changes at the same values
EI(+), ${E}_{I}^{(\ensuremath{-})}$ of the incident field. Below the critical density of atoms one recovers the usual picture of resonance fluorescence, with a continuous transition from a single-line spectrum to a three-peaked structure when the Rabi frequency becomes equal to the natural linewidth. Above the critical density the triplet appears only when the Rabi frequency becomes equal to the cooperative linewidth of pure super-fluorescence (i.e., for
EI=EI(+)). Moreover, it appears discontinuously: when
EI crosses the value
EI(+) the spectrum changes from a single narrow line to a triplet with well-separated sidebands.
One of the simplest models involving the atom-field interaction is the coupling of a single two-level atom with single-mode optical field. Under the rotating wave approximation, this problem is reduced to a form that can be solved exactly. But the approximation is only valid when the two levels are resonant or nearly resonant with the applied electromagnetic radiation. Here we present an analytical solution without the rotating wave approximation and applicable to general atom-field interaction far away from the resonance. We find that there exists remarkable influence of the initial phase of optical field on the Rabi oscillations and Rabi splitting, and this issue cannot be explored in the context of the rotating wave approximation. Due to the retention of the counter-rotating terms, higher-order harmonic appears during the Rabi splitting. The analytical solution suggests a way to regulate and control the quantum dynamics of a two-level atom and allows for exploring more essential features of the atom-field interaction.
The properties of a phase conjugate mirror (PCM) interacting radiatively with other objects are investigated. The spontaneous emission rate of a two-level atom (TLA) is attributed to the dipole emission of the upper energy level into vacuum field modes incident on the front face of the PCM, the emission into vacuum modes transmitted from the rear port of the PCM, enhanced by a factor 1 + R (R = reflectivity), and the emission of a photon while the atom is in the lower level, accompanied by annihilation of two pump photons, weighted by a factor of R per emitted photon. These processes lead to an enhancement factor of 1 + R for the spontaneous decay rate and a steady state upper level occupation probability R/(2R + 2), both in agreement with solution of the Heisenberg equations of TLA operators.1 The momentum transfer is zero, and the steady state emission rate is A12R(R + 2)/(2R + 2) photons/s atom. The stimulated emission and absorption constants are enhanced in a similar way. Contrary to the case of a conventional mirror, the Lippman fringes are present only for coherent radiation states.