The nonlinear dynamical effects of synchronization and bifurcations of Rabi oscillations and oscillations of the center of mass of an atom moving in the field of a standing light wave are theoretically and numerically examined. After completion of a transient process, synchronized oscillations, stable with respect to small noise, are established both upon ballistic motion of the atom and upon its oscillations in the optical potential well. The bifurcations of limit cycle generation with different periods (tripling of the period is most pronounced) and the passage to a chaotic strange attractor through an intermittency are obtained.
The nonlinear dynamical effects of synchronization and bifurcations of Rabi oscillations and oscillations of the center of mass of an atom moving in the field of a standing light wave are theoretically and numerically examined. After completion of a transient process, synchronized oscillations, stable with respect to small noise, are established both upon ballistic motion of the atom and upon its oscillations in the optical potential well. The bifurcations of limit cycle generation with different periods (tripling of the period is most pronounced) and the passage to a chaotic strange attractor through an intermittency are obtained.
We consider dissipative dynamics of atoms in a strong standing laser wave and find a nonlinear dynamical effect of synchronization between center-of-mass motion and internal Rabi oscillations. The synchronization manifests itself in the phase space as limit cycles, which may have different periods and riddled basins of attraction. The effect can be detected in fluorescence spectra of atoms as equidistant sideband frequencies with the space between adjacent peaks to be inversely proportional to the value of the period of the respective limit cycle. With increasing intensity of the laser field, we numerically observe cascades of bifurcations that eventually end up in settling a strange chaotic attractor. A broadband noise is shown to destroy a fine structure of the bifurcation scenario, but prominent features of period-1 and period-3 limit cycles survive under a weak noise. The character of the atomic motion is analyzed with the help of the friction force whose zeroes are attractor or repellor points in the velocity space. We find ranges of the laser parameters where the atomic motion resembles a random but deterministic walking of atoms erratically jumping between different wells of the optical potential. Such a random walking is shown to be fractal.
We treat semiclassical nonlinear dynamics of a two-level atom in the strong standing-wave field created in a high-quality cavity and in a free space with the help of two counterpropagating laser beams. First of all, we consider the dynamics of the strongly coupled atom-field system in an ideal cavity without any losses and discuss briefly nonlinear dynamical effects of random walking of an atom in a fully deterministic standing wave and Hamiltonian dynamical fractals. Then we study how these effects change in a free space when we take into account relaxation and external pumping of the standing wave. We discuss briefly new dissipative effects of synchronization between electronic and mechanical degrees of freedom of atoms, limit cycles of different periods and their bifurcations, and strange atomic attractors. Finally, we treat spontaneous relaxation as a random events in the equations of motion and study what happens with atomic fractality and limit cycles. It is shown that a self-similar structure of the scattering function (at least, on a few first levels) is conserved in the presence of spontaneous jumps. As to limit cycles, we could not resolve limit cycles of different period, but the fact of synchronization of internal and external atomic degrees of freedom is strictly established in the system with spontaneous jumps.
We study the coupled translational and internal dynamics of a two-level atom in a spatially periodic optical potential created by a single-mode field in a high-finesse Fabry-Perot cavity. The strongly coupled atom-cavity system with atomic center-of-mass motion included is modeled by semiclassical nonlinear Heisenberg equations of motion with two degrees of freedom. At exact resonance between the internal atomic transition and the cavity eigenfrequency, the internal and translational degrees of freedom are separated from each other resulting in periodically modulated Rabi oscillations and regular translational motion. Near the atom-field resonance, the coupled dynamics is found to be irregular and even chaotic in the sense of extremal sensitivity to initial conditions. It is manifested as a chaotic motion of an atom in an absolutely regular spatially periodic potential in the absence of any random fluctuations. This effect may be explained as a result of the interaction of nonlinear resonances in the atom-field nonlinear pendulum whose low-frequency translational motion is modulated by the high-frequency Rabi oscillations. The irregular motion is studied in detail in numerical experiments using the arsenal of methods of the dynamical systems theory. The results obtained are compared with recent experiments with ultracold single atoms interacting with single photons in the strong-coupling regime. We estimate the ranges of the system's control parameters, the detuning, the recoil frequency, and the mean number of intracavity photons, in which the interaction of nonlinear resonances may lead, under realistic conditions, to local instability of the center-of-mass motion and some manifestations of dynamical chaos, which is the effect of interest in studying the quantum-classical correspondence and quantum chaos in atomic optics.
The motion of a two-level atom with an internal degree of freedom that interacts with the field of a single-mode standing light wave in a high- Q cavity is treated as a scattering problem. At detunings between atomic and field resonances δ, atomic recoil frequencies α, initial atomic momenta ρ 0 , and numbers of excitations N at which the semiclassical equations have chaotic solutions (in the sense of their exponential sensitivity to small changes in the initial conditions), atomic scattering is fractal with strongly pronounced self-similarity of the dependence of time T at which the atom leaves the cavity at its initial momentum; the fractal dimension of this curve is 1.84. In the chaotic regime, there are two infinite sets of atomic initial momenta for which T =∞ (in the idealized case of the absence of any loss). They correspond to separatrix-like trajectories along which the atom asymptotically approaches certain configuration space points and to the trajectories of infinitely long chaotic wandering of atoms in the cavity. These trajectories make up countable and uncountable fractals, respectively. Correlations between Rabi atomic oscillations and atomic motion can lead to Doppler-Rabi resonances, that is, deep oscillations of the internal energy of the atom, for large detunings δ that satisfy the condition |αρ 0 |≈|δ|.
Strong coupling of the internal and external degrees of freedom of a cold atom to each other and to the spatially periodic field of the standing light wave in a high-finesse cavity is responsible for the dynamic instability of the atomic center-of-mass motion. Due to a weak interaction of the internal nonlinear resonances in the standard model of cavity QED, a stochastic layer appears, whose width in the semiclassical approximation is estimated in terms of the main parameters of the system: atomic recoil frequency, mean number of excitations, and detuning from the resonance. As a result, the atomic motion in the absolutely regular potential has the fractal character, with long Lévy flights alternating with small chaotic oscillations in potential wells.
We study dynamics of the atom-photon interaction in cavity quantum electrodynamics, considering a cold two-level atom in a single-mode high-finesse standing-wave cavity as a nonlinear Hamiltonian system with three coupled degrees of freedom: translational, internal atomic, and the field. The system proves to have different types of motion including Lévy flights and chaotic walkings of an atom in a cavity. The corresponding equations of motion for expectation values of the atom and field variables have two characteristic time scales: fast Rabi oscillations of the internal atomic and field quantities and slow translational oscillations of the center of the atom mass. It is shown that the translational motion, related to the atom recoils, is governed by an equation of a parametric nonlinear pendulum with a frequency modulated by the Rabi oscillations. This type of dynamics is chaotic with some width of the stochastic layer that is estimated analytically. The width is fairly small for realistic values of the control parameters, the normalized detuning delta and atomic recoil frequency alpha. We consider the Poincaré sections of the dynamics, compute the Lyapunov exponents, and find a range of the detuning, |delta| less, similar 3, where chaos is prominent. It is demonstrated how the atom-photon dynamics with a given value of alpha depends on the values of delta and initial conditions. Two types of Lévy flights, one corresponding to the ballistic motion of the atom and the other corresponding to small oscillations in a potential well, are found. These flights influence statistical properties of the atom-photon interaction such as distribution of Poincaré recurrences and moments of the atom position x. The simulation shows different regimes of motion, from slightly abnormal diffusion with <x(2)> approximately tau(1.13) at delta=1.2 to a superdiffusion with <x(2)> approximately tau(2.2) at delta=1.92 that corresponds to a superballistic motion of the atom with an acceleration. The obtained results can be used to find new ways to manipulate atoms, to cool and trap them by adjusting the detuning delta.