2,525 research outputs found
Direct numerical method for counting statistics in stochastic processes
We propose a direct numerical method to calculate the statistics of the
number of transitions in stochastic processes, without having to resort to
Monte Carlo calculations. The method is based on a generating function method,
and arbitrary moments of the probability distribution of the number of
transitions are in principle calculated by solving numerically a system of
coupled differential equations. As an example, a two state model with a
time-dependent transition matrix is considered and the first, second and third
moments of the current are calculated. This calculation scheme is applicable
for any stochastic process with a finite state space, and it would be helpful
to study current statistics in nonequilibrium systems.Comment: 8 pages, 2 figure
Noncyclic and nonadiabatic geometric phase for counting statistics
We propose a general framework of the geometric-phase interpretation for
counting statistics. Counting statistics is a scheme to count the number of
specific transitions in a stochastic process. The cumulant generating function
for the counting statistics can be interpreted as a `phase', and it is
generally divided into two parts: the dynamical phase and a remaining one. It
has already been shown that for cyclic evolution the remaining phase
corresponds to a geometric phase, such as the Berry phase or Aharonov-Anandan
phase. We here show that the remaining phase also has an interpretation as a
geometric phase even in noncyclic and nonadiabatic evolution.Comment: 12 pages, 1 figur
The stochastic pump current and the non-adiabatic geometrical phase
We calculate a pump current in a classical two-state stochastic chemical
kinetics by means of the non-adiabatic geometrical phase interpretation. The
two-state system is attached to two particle reservoirs, and under a periodic
perturbation of the kinetic rates, it gives rise to a pump current between the
two-state system and the absorbing states. In order to calculate the pump
current, the Floquet theory for the non-adiabatic geometrical phase is extended
from a Hermitian case to a non-Hermitian case. The dependence of the pump
current on the frequency of the perturbative kinetic rates is explicitly
derived, and a stochastic resonance-like behavior is obtained.Comment: 11 page
Current and fluctuation in a two-state stochastic system under non-adiabatic periodic perturbation
We calculate a current and its fluctuation in a two-state stochastic system
under a periodic perturbation. The system could be interpreted as a channel on
a cell surface or a single Michaelis-Menten catalyzing enzyme. It has been
shown that the periodic perturbation induces so-called pump current, and the
pump current and its fluctuation are calculated with the aid of the geometrical
phase interpretation. We give a simple calculation recipe for the statistics of
the current, especially in a non-adiabatic case. The calculation scheme is
based on the non-adiabatic geometrical phase interpretation. Using the Floquet
theory, the total current and its fluctuation are calculated, and it is
revealed that the average of the current shows a stochastic-resonance-like
behavior. In contrast, the fluctuation of the current does not show such
behavior.Comment: 7 pages, 1 figur
In-situ photoemission study of Pr_{1-x}Ca_xMnO_3 epitaxial thin films with suppressed charge fluctuations
We have performed an {\it in-situ} photoemission study of Pr_{1-x}Ca_xMnO_3
(PCMO) thin films grown on LaAlO_3 (001) substrates and observed the effect of
epitaxial strain on the electronic structure. We found that the chemical
potential shifted monotonically with doping, unlike bulk PCMO, implying the
disappearance of incommensurate charge fluctuations of bulk PCMO. In the
valence-band spectra, we found a doping-induced energy shift toward the Fermi
level (E_F) but there was no spectral weight transfer, which was observed in
bulk PCMO. The gap at E_F was clearly seen in the experimental band dispersions
determined by angle-resolved photoemission spectroscopy and could not be
explained by the metallic band structure of the C-type antiferromagnetic state,
probably due to localization of electrons along the ferromagnetic chain
direction or due to another type of spin-orbital ordering.Comment: 5 pages, 4 figure
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