109 research outputs found
Resonant control of cold-atom transport through two optical lattices with a constant relative speed
We show theoretically that the dynamics of cold atoms in the lowest energy
band of a stationary optical lattice can be transformed and controlled by a
second, weaker, periodic potential moving at a constant speed along the axis of
the stationary lattice. The atom trajectories exhibit complex behavior, which
depends sensitively on the amplitude and speed of the propagating lattice. When
the speed and amplitude of the moving potential are low, the atoms are dragged
through the static lattice and perform drifting orbits with frequencies an
order of magnitude higher than that corresponding to the moving potential.
Increasing either the speed or amplitude of the moving lattice induces
Bloch-like oscillations within the energy band of the static lattice, which
exhibit complex resonances at critical values of the system parameters. In some
cases, a very small change in these parameters can reverse the atom's direction
of motion. In order to understand these dynamics we present an analytical
model, which describes the key features of the atom transport and also
accurately predicts the positions of the resonant features in the atom's phase
space. The abrupt controllable transitions between dynamical regimes, and the
associated set of resonances, provide a mechanism for transporting atoms
between precise locations in a lattice: as required for using cold atoms to
simulate condensed matter or as a stepping stone to quantum information
processing. The system also provides a direct quantum simulator of acoustic
waves propagating through semiconductor nanostructures in sound analogs of the
optical laser (SASER)
Nonlinear dynamics and band transport in a superlattice driven by a plane wave
A quantum particle transport induced in a spatially-periodic potential by a
propagating plane wave has a number important implications in a range of
topical physical systems. Examples include acoustically driven semiconductor
superlattices and cold atoms in optical crystal. Here we apply kinetic
description of the directed transport in a superlattice beyond standard linear
approximation, and utilize exact path-integral solutions of the semiclassical
transport equation. We show that the particle drift and average velocities have
non-monotonic dependence on the wave amplitude with several prominent extrema.
Such nontrivial kinetic behaviour is related to global bifurcations developing
with an increase of the wave amplitude. They cause dramatic transformations of
the system phase space and lead to changes of the transport regime. We describe
different types of phase trajectories contributing to the directed transport
and analyse their spectral content
Controlling high-frequency collective electron dynamics via single-particle complexity
We demonstrate, through experiment and theory, enhanced high-frequency
current oscillations due to magnetically-induced conduction resonances in
superlattices. Strong increase in the ac power originates from complex
single-electron dynamics, characterized by abrupt resonant transitions between
unbound and localized trajectories, which trigger and shape propagating charge
domains. Our data demonstrate that external fields can tune the collective
behavior of quantum particles by imprinting configurable patterns in the
single-particle classical phase space.Comment: 5 pages, 4 figure
Towards the Heisenberg limit in microwave photon detection by a qubit array
Using an analytically solvable model, we show that a qubit array-based
detector allows to achieve the fundamental Heisenberg limit in detecting single
photons. In case of superconducting qubits, this opens new opportunities for
quantum sensing and communications in the important microwave range.Comment: 6 pages, 3 figure
Using acoustic waves to induce high-frequency current oscillations in superlattices
We show that GHz acoustic waves in semiconductor superlattices can induce THz
electron dynamics that depend critically on the wave amplitude. Below a
threshold amplitude, the acoustic wave drags electrons through the superlattice
with a peak drift velocity overshooting that produced by a static electric
field. In this regime, single electrons perform drifting orbits with THz
frequency components. When the wave amplitude exceeds the critical threshold,
an abrupt onset of Bloch-like oscillations causes negative differential
velocity. The acoustic wave also affects the collective behavior of the
electrons by causing the formation of localised electron accumulation and
depletion regions, which propagate through the superlattice, thereby producing
self-sustained current oscillations even for very small wave amplitudes. We
show that the underlying single-electron dynamics, in particular the transition
between the acoustic wave dragging and Bloch oscillation regimes, strongly
influence the spatial distribution of the electrons and the form of the current
oscillations. In particular, the amplitude of the current oscillations depends
non-monotonically on the strength of the acoustic wave, reflecting the
variation of the single-electron drift velocity.Comment: 10 pages, 8 figure
Bifurcations and chaos in semiconductor superlattices with a tilted magnetic field
We study the effects of dissipation on electron transport in a semiconductor
superlattice with an applied bias voltage and a magnetic field that is tilted
relative to the superlattice axis.In previous work, we showed that although the
applied fields are stationary,they act like a THz plane wave, which strongly
couples the Bloch and cyclotron motion of electrons within the lowest miniband.
As a consequence,the electrons exhibit a unique type of Hamiltonian chaos,
which creates an intricate mesh of conduction channels (a stochastic web) in
phase space, leading to a large resonant increase in the current flow at
critical values of the applied voltage. This phase-space patterning provides a
sensitive mechanism for controlling electrical resistance. In this paper, we
investigate the effects of dissipation on the electron dynamics by modifying
the semiclassical equations of motion to include a linear damping term. We
demonstrate that even in the presence of dissipation,deterministic chaos plays
an important role in the electron transport process. We identify mechanisms for
the onset of chaos and explore the associated sequence of bifurcations in the
electron trajectories. When the Bloch and cyclotron frequencies are
commensurate, complex multistability phenomena occur in the system. In
particular, for fixed values of the control parameters several distinct stable
regimes can coexist, each corresponding to different initial conditions. We
show that this multistability has clear, experimentally-observable, signatures
in the electron transport characteristics.Comment: 14 pages 11 figure
Semiconductor charge transport driven by a picosecond strain pulse
We demonstrate that a picosecond strain pulse can be used to drive an electric current through both thin-film epilayer and heterostructure semiconductor crystals in the absence of an external electric field. By measuring the transient current pulses, we are able to clearly distinguish the effects of the coherent and incoherent components of the acoustic packet. The properties of the strain induced signal suggest a technique for exciting picosecond current pulses, which may be used to probe semiconductor devices
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