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P. V. Elyutin

Publications and source records attributed to P. V. Elyutin.

9 recordsLinked to original sources

On the interaction of a single-photon wave packet with an excited atom

The interaction of a single-photon wave packet with an initially excited two-level atom in free space is studied in semiclassical and quantum approaches. It is shown that the final state of the field does not contain doubly occupied modes. The process of the atom's transition to the ground state may be accelerated, decelerated or even reversed by the incoming photon, depending on parameters. The spectrum of emitted radiation is close to the sum of the spectrum of the incoming single-photon wave packet and the natural line shape, with small and complicated deviations.

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Natural line shape

The observable line shape of the spontaneous emission depends on the procedure of atom's excitation. The spectrum of radiation emitted by a two-level atom excited from the ground state by a pi pulse of the resonant pump field is calculated for the case when the Rabi frequency is much larger than the relaxation rate. It is shown that the central part of the spectral distribution has a standard Lorentzian form, whereas for detunings from the resonance that are larger than the Rabi frequency the spectral density falls off faster. The shape of the wings of the spectral line is sensitive to the form of the pi pulse. The implications for the quantum Zeno effect theory and for the estimates of the duration of quantum jumps are discussed.

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Energy diffusion in strongly driven quantum chaotic systems: Role of correlations of the matrix elements

The energy evolution of a quantum chaotic system under the perturbation that harmonically depends on time is studied for the case of large perturbation, in which the rate of transition calculated from the Fermi golden rule (FGR) is about or exceeds the frequency of perturbation. For this case the models of Hamiltonian with random non-correlated matrix elements demonstrate that the energy evolution retains its diffusive character, but the rate of diffusion increases slower than the square of the magnitude of perturbation, thus destroying the quantum-classical correspondence for the energy diffusion and the energy absorption in the classical limit $\hbar \to 0$. The numerical calculation carried out for a model built from the first principles (the quantum analog of the Pullen - Edmonds oscillator) demonstrates that the evolving energy distribution, apart from the diffusive component, contains a ballistic one with the energy dispersion that is proportional to the square of time. This component originates from the chains of matrix elements with correlated signs and vanishes if the signs of matrix elements are randomized. The presence of the ballistic component formally extends the applicability of the FGR to the non-perturbative domain and restores the quantum-classical correspondence.

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Energy diffusion in strongly driven quantum chaotic systems

The energy evolution of a quantum chaotic system under the perturbation that harmonically depends on time is studied for the case of large perturbation, in which the rate of transition calculated from the Fermi golden rule exceeds the frequency of perturbation. It is shown that the energy evolution retains its diffusive character, with the diffusion coefficient that is asymptotically proportional to the magnitude of perturbation and to the square root of the density of states. The results are supported by numerical calculation. They imply the absence of the quantum-classical correspondence for the energy diffusion and the energy absorption in the classical limit $\hbar \to 0$.

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Spiraling of adjacent trajectories in chaotic systems

The spiraling of adjacent trajectories in chaotic dynamical systems can be characterized by distribution of local angular velocities of rotation of the displacement vector, which is governed by linearized equations of motion. This distribution, akin to that of local Lyapunov exponents, is studied for three examples of three-dimensional flows. Toy model shows that the rotation rate of adjacent trajectories influences on the rate of mixing of dynamic variables and on the sensitivity of trajectories to perturbations.

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Lyapunov exponent for a gas of soft scatterers

For a fast particle moving within a two-dimensional array of soft scatterers - centers of weak and short-range potential - the dependence of the Lyapunov exponent on the system parameters is studied. The use of the linearized equations for variations of the propagation angles and impact parameters of consequent collisions reduces the problem to that of calculation of the Lyapunov exponent of an ensemble of strongly correlated random matrices with given statistics of matrix elements. In the simplest approximation this Lyapunov exponent is proportional to the interaction strength and inversely proportional to the square root of the interaction range. The model satisfactorily describes the intensity of chaos in a system of two weakly interacting particles moving in a two-dimensional regular confining potential.

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Gibbs attractor: a chaotic nearly Hamiltonian system, driven by external harmonic force

A chaotic autonomous Hamiltonian systems, perturbed by small damping and small external force, harmonically dependent on time, can acquire a strange attractor with properties similar to that of the canonical distribution - the Gibbs attractor. The evolution of the energy in such systems can be described as the energy diffusion. For the nonlinear Pullen - Edmonds oscillator with two degrees of freedom the properties of the Gibbs attractor and their dependence on parameters of the perturbation are studied both analytically and numerically.

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On the influence of noise on chaos in nearly Hamiltonian systems

The simultaneous influence of small damping and white noise on Hamiltonian systems with chaotic motion is studied on the model of periodically kicked rotor. In the region of parameters where damping alone turns the motion into regular, the level of noise that can restore the chaos is studied. This restoration is created by two mechanisms: by fluctuation induced transfer of the phase trajectory to domains of local instability, that can be described by the averaging of the local instability index, and by destabilization of motion within the islands of stability by fluctuation induced parametric modulation of the stability matrix, that can be described by the methods developed in the theory of Anderson localization in one-dimensional systems.

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On stimulated transitions between the self-trapped states of the nonlinear Schrodinger equation

The studied model describes a particle that obeys a one-dimensional nonlinear Schrödinger equation in the potential of a double-well. Transitions between the two lowest self-trapped states of this system under the influence of the external time-dependent perturbation are studied in the two-mode approximation. If the perturbation dependence on time is harmonic with the frequency $ω$, then transitions between the states become possible if the amplitude of the perturbation $F$ exceeds some threshold value $F_c(ω)$; above the threshold motion of the system becomes chaotic. If the perturbation is a broadband noise, then transitions between the states are possible at arbitrarily small $F$ and occur in the process of the system's energy diffusion.

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