Saturation of dephasing time in mesoscopic devices produced by a ferromagnetic state

We consider an exchange model of itinerant electrons in a Heisenberg ferromagnet and we assume that the ferromagnet is in a fully polarized state. Using the Holstein-Primakoff transformation we are able to obtain a boson-fermion Hamiltonian that is well-known in the interaction between light and matter. This model describes the spontaneous emission in two-level atoms that is the proper decoherence mechanism when the number of modes of the radiation field is taken increasingly large, the vacuum acting as a reservoir. In the same way one can see that the interaction between the bosonic modes of spin waves and an itinerant electron produces decoherence by spin flipping with a rate proportional to the size of the system. In this way we are able to show that the experiments on quantum dots, described in D. K. Ferry et al. [Phys. Rev. Lett. {\bf 82}, 4687 (1999)], and nanowires, described in D. Natelson et al. [Phys. Rev. Lett. {\bf 86}, 1821 (2001)], can be understood as the interaction of itinerant electrons and an electron gas in a fully polarized state.Comment: 10 pages, no figure. Changed title. Revised version accepted for publication in Physical Review

Scanning Fourier Spectroscopy: A microwave analog study to image transmission paths in quantum dots

We use a microwave cavity to investigate the influence of a movable absorbing center on the wave function of an open quantum dot. Our study shows that the absorber acts as a position-selective probe, which may be used to suppress those wave function states that exhibit an enhancement of their probability density near the region where the impurity is located. For an experimental probe of this wave function selection, we develop a technique that we refer to as scanning Fourier spectroscopy, which allows us to identify, and map out, the structure of the classical trajectories that are important for transmission through the cavity.Comment: 4 pages, 5 figure

Transport spectroscopy in a time-modulated open quantum dot

We have investigated the time-modulated coherent quantum transport phenomena in a ballistic open quantum dot. The conductance $G$ and the electron dwell time in the dots are calculated by a time-dependent mode-matching method. Under high-frequency modulation, the traversing electrons are found to exhibit three types of resonant scatterings. They are intersideband scatterings: into quasibound states in the dots, into true bound states in the dots, and into quasibound states just beneath the subband threshold in the leads. Dip structures or fano structures in $G$ are their signatures. Our results show structures due to 2$\hbar\omega$ intersideband processes. At the above scattering resonances, we have estimated, according to our dwell time calculation, the number of round-trip scatterings that the traversing electrons undertake between the two dot openings.Comment: 8 pages, 5 figure

Fractal Basins In Hénon-heiles And Other Polynomial Potentials

The dynamics of several Hamiltonian systems of two degrees of freedom with polynomial potentials is examined. All these systems present unbounded trajectories escaping along different routes. The motion in these open systems is characterized by a fractal boundary (and its corresponding fractal dimension) separating the basins of the escape routes. The fractal (basin boundary) dimensions for these systems are studied in some detail. © 1999 Elsevier Science B.V. All rights reserved.2565-6362368Contopoulos, G., (1990) Astron. Astrophys., 231, p. 41Contopoulos, G., Kaufmann, D., (1992) Astron. Astrophys., 253, p. 379Contopoulos, G., Polymilis, C., (1993) Phys. Rev. E, 46, p. 1546Contopoulos, G., Kandrup, H.E., Kaufmann, D., (1993) Phys. D, 64, p. 310Podolský, J., Veselý, K., (1998) Phys. Rev. D, 58. , 081501, gr-qc 9805078Podolský, J., Veselý, K., Chaotic Motion in pp-wave Spacetimes, , Preprint: gr-qc 9809065Ott, E., (1993) Chaos in Dynamical Systems, , Cambridge University Press, CambridgeHénon, M., Heiles, C., (1964) Astron. J., 69, p. 73Churchill, R.C., Pecelli, G., Rod, D.L., (1975) J. Diff. Equ., 17, p. 329Churchill, R.C., Rod, D.L., (1976) J. Diff. Equ., 21, p. 39(1976) J. Diff. Equ., 21, p. 66(1977) J. Diff. Equ., 24, p. 329Bleher, S., Grebogi, C., Ott, E., Brown, R., (1988) Phys. Rev. A, 38, p. 930Jánosi, I.M., Tél, T., Wolf, D.E., Gallas, J.A.C., (1997) Phys. Rev. E, 56, p. 285

Dynamical collapse of trajectories, part II: Limit set of a horseshoe-like map

The dynamics and limit set of a discrete-time system is described which is similar to the horseshoe map of Smale. The particular characteristics of this map are motivated by the study of mechanical systems with dry friction, where, as is discussed in the companion paper [Biemond, J.J.B. et. al., Dynamical collapse of trajectories, part I: Homoclinic tangles in systems with dry friction, submitted to Proc. ENOC 2014], homoclinic orbits can exist that emanate from sets of non-isolated equilibrium points, and the dynamics near these orbits is described by a non-invertible return map. The dynamics of the horseshoe-like nonsmooth map is shown to be topologically conjugate to a symbolic dynamics. While trajectories of this map can be continued uniquely in the forward direction of time, only in a subset of the state space, a unique continuation exists for the trajectory in the backward time direction. The same property is introduced in the symbolic dynamics by defining this dynamics as a shift on a quotient space of the standard symbolic state space with infinite strings of two symbols. Using the mentioned conjugacy, it is proven that the limit set contains an infinite number of periodic orbits

Dynamical collapse of trajectories, part I: homoclinic tangles in systems with dry friction

Dry friction induces unexpected dynamical behaviour, causing distinct trajectories to collapse onto a single point in finite time. The result is that transversal homoclinic orbits generate chaotic saddles with forward dynamics that is qualitatively different from the backward dynamics. The space of initial conditions converging to the chaotic saddle is fractal, but the set of points diverging from it is not: friction destroys the complexity of the forward dynamics by generating a unique horseshoe-like topology

Dynamical collapse of trajectories, part I: homoclinic tangles in systems with dry friction

Dry friction induces unexpected dynamical behaviour, causing distinct trajectories to collapse onto a single point in finite time. The result is that transversal homoclinic orbits generate chaotic saddles with forward dynamics that is qualitatively different from the backward dynamics. The space of initial conditions converging to the chaotic saddle is fractal, but the set of points diverging from it is not: friction destroys the complexity of the forward dynamics by generating a unique horseshoe-like topology