1,156 research outputs found
Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources
We investigate the superconducting lifetime of long current-biased Josephson
junctions, in the presence of Gaussian and non-Gaussian noise sources. In
particular, we analyze the dynamics of a Josephson junction as a function of
the noise signal intensity, for different values of the parameters of the
system and external driving currents. We find that the mean lifetime of the
superconductive state is characterized by nonmonotonic behavior as a function
of noise intensity, driving frequency and junction length. We observe that
these nonmonotonic behaviours are connected with the dynamics of the junction
phase string during the switching towards the resistive state. An important
role is played by the formation and propagation of solitons, with two different
dynamical regimes characterizing the dynamics of the phase string. Our analysis
allows to evidence the effects of different bias current densities, that is a
simple spatially homogeneous distribution and a more realistic inhomogeneous
distribution with high current values at the junction edges. Stochastic
resonant activation, noise enhanced stability and temporary trapping phenomena
are observed in the system investigated.Comment: 16 pages, 9 figures, Physical Review B, in pres
Uhlmann curvature in dissipative phase transitions
We study the mean Uhlmann curvature in fermionic systems undergoing a
dissipative driven phase transition. We consider a paradigmatic class of
lattice fermion systems in non-equilibrium steady-state of an open system with
local reservoirs, which are characterised by a Gaussian fermionic steady state.
In the thermodynamical limit, in systems with translational invariance we show
that a singular behaviour of the Uhlmann curvature represents a sufficient
criterion for criticalities, in the sense of diverging correlation length, and
it is not otherwise sensitive to the closure of the Liouvillian dissipative
gap. In finite size systems, we show that the scaling behaviour of the mean
Uhlmann curvature maps faithfully the phase diagram, and a relation to the
dissipative gap is put forward. We argue that the mean Uhlmann phase can shade
light upon the nature of non equilibrium steady state criticality in particular
with regard to the role played by quantum vs classical fluctuations.Comment: 5 pages, 3 figures with appendix of 10 pages, 1 figur
Quantum resonant activation
Quantum resonant activation is investigated for the archetype setup of an
externally driven two-state (spin-boson) system subjected to strong dissipation
by means of both analytical and extensive numerical calculations. The
phenomenon of resonant activation emerges in the presence of either randomly
fluctuating or deterministic periodically varying driving fields. Addressing
the incoherent regime, a characteristic minimum emerges in the mean first
passage time to reach an absorbing neighboring state whenever the intrinsic
time scale of the modulation matches the characteristic time scale of the
system dynamics. For the case of deterministic periodic driving, the first
passage time probability density function (pdf) displays a complex,
multi-peaked behavior, which depends crucially on the details of initial phase,
frequency, and strength of the driving. As an interesting feature we find that
the mean first passage time enters the resonant activation regime at a critical
frequency which depends very weakly on the strength of the driving.
Moreover, we provide the relation between the first passage time pdf and the
statistics of residence times.Comment: 14 pages, 13 figure
Quantum dissipative dynamics of a bistable system in the sub-Ohmic to super-Ohmic regime
We investigate the quantum dynamics of a multilevel bistable system coupled
to a bosonic heat bath beyond the perturbative regime. We consider different
spectral densities of the bath, in the transition from sub-Ohmic to super-Ohmic
dissipation, and different cutoff frequencies. The study is carried out by
using the real-time path integral approach of the Feynman-Vernon influence
functional. We find that, in the crossover dynamical regime characterized by
damped \emph{intrawell} oscillations and incoherent tunneling, the short time
behavior and the time scales of the relaxation starting from a nonequilibrium
initial condition depend nontrivially on the spectral properties of the heat
bath.Comment: 16 pages, 7 figure
Effects of L\'evy noise on the dynamics of sine-Gordon solitons in long Josephson junctions
We numerically investigate the generation of solitons in current-biased long
Josephson junctions in relation to the superconducting lifetime and the voltage
drop across the device. The dynamics of the junction is modelled with a
sine-Gordon equation driven by an oscillating field and subject to an external
non-Gaussian noise. A wide range of -stable L\'evy distributions is
considered as noise source, with varying stability index and asymmetry
parameter . In junctions longer than a critical length, the mean
switching time (MST) from superconductive to the resistive state assumes a
values independent of the device length. Here, we demonstrate that such a value
is directly related to the mean density of solitons which move into or from the
washboard potential minimum corresponding to the initial superconductive state.
Moreover, we observe: (i) a connection between the total mean soliton density
and the mean potential difference across the junction; (ii) an inverse behavior
of the mean voltage in comparison with the MST, with varying the junction
length; (iii) evidences of non-monotonic behaviors, such as stochastic resonant
activation and noise enhanced stability, of MST versus the driving frequency
and noise intensity for different values of and ; (iv) finally,
these non-monotonic behaviors are found to be related to the mean density of
solitons formed along the junction.Comment: 24 pages, 8 figures, submitted to J. Stat. Mech.: Theory Exp. arXiv
admin note: text overlap with arXiv:1406.481
Lifetime of the superconductive state in short and long Josephson junctions
We study the transient statistical properties of short and long Josephson
junctions under the influence of thermal and correlated fluctuations. In
particular, we investigate the lifetime of the superconductive metastable state
finding the presence of noise induced phenomena. For short Josephson junctions
we investigate the lifetime as a function both of the frequency of the current
driving signal and the noise intensity and we find how these noise-induced
effects are modified by the presence of a correlated noise source. For long
Josephson junctions we integrate numerically the sine-Gordon equation
calculating the lifetime as a function of the length of the junction both for
inhomogeneous and homogeneous bias current distributions. We obtain a
nonmonotonic behavior of the lifetime as a function of the frequency of the
current driving signal and the correlation time of the noise. Moreover we find
two maxima in the nonmonotonic behaviour of the mean escape time as a function
of the correlated noise intensity.Comment: 12 pages, 9 figure
A stochastic interspecific competition model to predict the behaviour of Listeria monocytogenes in the fermentation process of a traditional Sicilian salami
The present paper discusses the use of modified Lotka-Volterra equations in
order to stochastically simulate the behaviour of Listeria monocytogenes and
Lactic Acid Bacteria (LAB) during the fermentation period (168 h) of a typical
Sicilian salami. For this purpose, the differential equation system is set
considering T, pH and aw as stochastic variables. Each of them is governed by
dynamics that involve a deterministic linear decrease as a function of the time
t and an "additive noise" term which instantaneously mimics the fluctuations of
T, pH and aw. The choice of a suitable parameter accounting for the interaction
of LAB on L. monocytogenes as well as the introduction of appropriate noise
levels allows to match the observed data, both for the mean growth curves and
for the probability distribution of L. monocytogenes concentration at 168 h.Comment: 19 pages, 2 figures, 2 tables. To be published in Eur. Food Res.
Techno
Sine-Gordon breathers generation in driven long Josephson junctions
We consider a long Josephson junction excited by a suitable external
ac-signal, in order to generate control and detect breathers. Studying the
nonlinear supratransmission phenomenon in a nonlinear sine-Gordon chain
sinusoidally driven, Geniet and Leon explored the bifurcation of the energy
transmitted into the chain and calculated a threshold for the
external driving signal amplitude, at which the energy flows into the system by
breathers modes. I numerically study the continuous sine-Gordon model,
describing the dynamics of the phase difference in a long Josephson junction,
in order to deeply investigate the "continuous limit" modifications to this
threshold. Wherever the energy flows into the system due to the nonlinear
supratransmission, a peculiar breather localization areas appear in a parameters space. The emergence of these areas depends on the damping
parameter value, the bias current, and the waveform of driving external signal.
The robustness of generated breathers is checked by introducing into the model
a thermal noise source to mimic the environmental fluctuations. Presented
results allows one to consider a cryogenic experiment for creation and
detection of Josephson breathers.Comment: 8 pages, 3 figure
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