35 research outputs found
Directed transport born from chaos in asymmetric antidot structures
It is shown that a polarized microwave radiation creates directed transport
in an asymmetric antidot superlattice in a two dimensional electron gas. A
numerical method is developed that allows to establish the dependence of this
ratchet effect on several parameters relevant for real experimental studies. It
is applied to the concrete case of a semidisk Galton board where the electron
dynamics is chaotic in the absence of microwave driving. The obtained results
show that high currents can be reached at a relatively low microwave power.
This effect opens new possibilities for microwave control of transport in
asymmetric superlattices.Comment: 8 pages, 10 figure
Transport and dynamical properties of inertial ratchets
In this paper we discuss the dynamics and transport properties of a massive
particle, in a time dependent periodic potential of the ratchet type, with a
dissipative environment. The directional currents and characteristics of the
motion are studied as the specific frictional coefficient varies, finding that
the stationary regime is strongly dependent on this parameter. The maximal
Lyapunov exponent and the current show large fluctuations and inversions,
therefore for some range of the control parameter, this inertial ratchet could
originate a mass separation device. Also an exploration of the effect of a
random force on the system is performed.Comment: PDF, 16 pages, 7 figure
Photogalvanic current in artificial asymmetric nanostructures
We develop a theoretic description of the photogalvanic current induced by a
high frequency radiation in asymmetric nanostructures and show that it
describes well the results of numerical simulations. Our studies allow to
understand the origin of the electronic ratchet transport in such systems and
show that they can be used for creation of new types of detectors operating at
room temperature in a terahertz radiation range.Comment: 11 pages, 9 figs, EPJ latex styl
Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance
We theoretically study the influence of the noise strength on the excitation
of the Brillouin propagation modes in a dissipative optical lattice. We show
that the excitation has a resonant behavior for a specific amount of noise
corresponding to the precise synchronization of the Hamiltonian motion on the
optical potential surfaces and the dissipative effects associated with optical
pumping in the lattice. This corresponds to the phenomenon of stochastic
resonance. Our results are obtained by numerical simulations and correspond to
the analysis of microscopic quantities (atomic spatial distributions) as well
as macroscopic quantities (enhancement of spatial diffusion and pump-probe
spectra). We also present a simple analytical model in excellent agreement with
the simulations
Characterisation of a three-dimensional Brownian motor in optical lattices
We present here a detailed study of the behaviour of a three dimensional
Brownian motor based on cold atoms in a double optical lattice [P. Sjolund et
al., Phys. Rev. Lett. 96, 190602 (2006)]. This includes both experiments and
numerical simulations of a Brownian particle. The potentials used are spatially
and temporally symmetric, but combined spatiotemporal symmetry is broken by
phase shifts and asymmetric transfer rates between potentials. The diffusion of
atoms in the optical lattices is rectified and controlled both in direction and
speed along three dimensions. We explore a large range of experimental
parameters, where irradiances and detunings of the optical lattice lights are
varied within the dissipative regime. Induced drift velocities in the order of
one atomic recoil velocity have been achieved.Comment: 8 pages, 14 figure
Control of Current Reversal in Single and Multiparticle Inertia Ratchets
We have studied the deterministic dynamics of underdamped single and
multiparticle ratchets associated with current reversal, as a function of the
amplitude of the external driving force. Two experimentally inspired methods
are used. In the first method the same initial condition is used for each new
value of the amplitude. In the second method the last position and velocity is
used as the new initial condition when the amplitude is changed. The two
methods are found to be complementary for control of current reversal, because
the first one elucidates the existence of different attractors and gives
information about their basins of attraction, while the second method, although
history dependent, shows the locking process. We show that control of current
reversals in deterministic intertia ratchets is possible as a consequence of a
locking process associated with different mean velocity attractors. An
unlocking efect is produced when a chaos to order transition limits the control
range.Comment: to be published in Physica A - 11 pages - 10 figure
Brillouin propagation modes in optical lattices: Interpretation in terms of nonconventional stochastic resonance
We report the first direct observation of Brillouin-like propagation modes in a dissipative periodic optical lattice. This has been done by observing a resonant behavior of the spatial diffusion coefficient in the direction corresponding to the propagation mode with the phase velocity of the moving intensity modulation used to excite these propagation modes. Furthermore, we show theoretically that the amplitude of the Brillouin mode is a nonmonotonic function of the strength of the noise corresponding to the optical pumping, and discuss this behavior in terms of nonconventional stochastic resonance
Efficiency optimization in a correlation ratchet with asymmetric unbiased fluctuations
The efficiency of a Brownian particle moving in periodic potential in the
presence of asymmetric unbiased fluctuations is investigated. We found that
there is a regime where the efficiency can be a peaked function of temperature,
which proves that thermal fluctuations facilitate the efficiency of energy
transformation, contradicting the earlier findings (H. kamegawa et al. Phys.
Rev. Lett. 80 (1998) 5251). It is also found that the mutual interplay between
asymmetry of fluctuation and asymmetry of the potential may induce optimized
efficiency at finite temperature. The ratchet is not most efficiency when it
gives maximum current.Comment: 10 pages, 7 figure
Rectification and Phase Locking for Particles on Two Dimensional Periodic Substrates
We show that a novel rectification phenomena is possible for overdamped
particles interacting with a 2D periodic substrate and driven with a
longitudinal DC drive and a circular AC drive. As a function of DC amplitude,
the longitudinal velocity increases in a series of quantized steps with
transverse rectification occuring near these transitions. We present a simple
model that captures the quantization and rectification behaviors.Comment: 4 pages, 4 postscript figure
Molecular motor that never steps backwards
We investigate the dynamics of a classical particle in a one-dimensional
two-wave potential composed of two periodic potentials, that are
time-independent and of the same amplitude and periodicity. One of the periodic
potentials is externally driven and performs a translational motion with
respect to the other. It is shown that if one of the potentials is of the
ratchet type, translation of the potential in a given direction leads to motion
of the particle in the same direction, whereas translation in the opposite
direction leaves the particle localized at its original location. Moreover,
even if the translation is random, but still has a finite velocity, an
efficient directed transport of the particle occurs.Comment: 4 pages, 5 figures, Phys. Rev. Lett. (in print