Chaotic quantum phenomena without classical counterpart

Fast physical random-number generation based on room-temperature chaotic oscillations in weakly coupled superlattices

An all-electronic physical random number generator at rates up to 80  Gbit/s is presented, based on weakly coupled GaAs/Ga0.55Al0.45As superlattices operated at room temperature. It is based on large-amplitude, chaotic current oscillations characterized by a bandwidth of several hundred MHz and do not require external feedback or conversion to an electronic signal prior to digitization. The method is robust and insensitive to external perturbations and its fully electronic implementation suggests scalability and minimal postprocessing in comparison to existing optical implementations.

Dynamics of kicked particles in a double-barrier structure

We study the classical and quantum dynamics of periodically kicked particles placed initially within an open double-barrier structure. This system does not obey the Kolmogorov-Arnold-Moser (KAM) theorem and displays chaotic dynamics. The phase-space features induced by non-KAM nature of the system lead to dynamical features such as the nonequilibrium steady state, classically induced saturation of energy growth and momentum filtering. We also comment on the experimental feasibility of this system as well as its relevance in the context of current interest in classically induced localization and chaotic ratchets.

Chaotic properties of quantum transport in Ni-Nb-Zr-H glassy alloys

We analyzed the dynamic evolution of an ensemble of electrons performing macroscopic resonant tunneling for room-temperature millimeter-sized Coulomb oscillation in Ni-Nb-Zr-H glassy alloys as a function of the cluster size and boundary length using a one-dimensional Kronig-Penny model with a stepwise potential. The reflection coefficient showed a stagnant chaos around a narrow torus for a superlattice with a cluster size of 0.55 nm and a boundary distance of 0.23 nm. The transmission and reflection coefficients showed stationary chaotic behavior in periodic units with decreasing boundary distance rather than increasing cluster size.

Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures

The dynamic interplay of transport, electrostatic, and magnetic effects in the resonant tunneling through ferromagnetic quantum wells is theoretically investigated. It is shown that the carrier-mediated magnetic order in the ferromagnetic region not only induces, but also takes part in intrinsic, robust, and sustainable high-frequency current oscillations over a large window of nominally steady bias voltages. This phenomenon could spawn a new class of quantum electronic devices based on ferromagnetic semiconductors.

Quantum breaking time near classical equilibrium points

In the evolution of distributions localized around classical equilibrium points, the quantum-classical correspondence breaks down at a time, the so-called quantum breaking, or Ehrenfest time, which is related to the minimal separation of the quantum levels in proximity of the classical equilibrium energy. By studying one-dimensional systems with single- and double-well polynomial potentials, we find that the Ehrenfest time diverges logarithmically with the inverse of the Planck constant whenever the equilibrium point is exponentially unstable. In all the other cases, we have a power law divergence with the exponent determined by the degree of the potential near the equilibrium point.

Dynamical mean-field solution of coupled quantum wells: a bifurcation analysis

The time evolution of a discrete model of three quantum wells with a localized mean-field electrostatic interaction has been analyzed making use of numerical simulation and bifurcation techniques. The discrete Schrödinger equation can be written as a classical Hamiltonian system with two constants of motion. The frequency spectrum and the Lyapunov exponents show that the system is chaotic as its continuum counterpart. The organizing centers of the dynamical behavior are bifurcations of rotating periodic solutions whose simple structure allows a thorough analytical investigation as the conserved quantities are varied. The global structure of the periodic behavior is organized via subharmonic bifurcations at which tori of nonsymmetric periodic solutions are born. We have found another kind of bifurcation when two pairs of characteristic multipliers split from the unit circle. The chaotic behavior is related to the nonintegrability of the system.