197 research outputs found
The nature and boundary of the floating phase in a dissipative Josephson junction array
We study the nature of correlations within, and the transition into, the
floating phase of dissipative Josephson junction arrays. Order parameter
correlations in this phase are long-ranged in time, but only short-ranged in
space. A perturbative RG analysis shows that, in {\it arbitrary} spatial
dimension, the transition is controlled by a continuous locus of critical fixed
points determined entirely by the \textit{local} topology of the lattice. This
may be the most natural example of a line of critical points existing in
arbitrary dimensions.Comment: Parts rewritten, typos correcte
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
A cluster algorithm for resistively shunted Josephson junctions
We present a cluster algorithm for resistively shunted Josephson junctions
and similar physical systems, which dramatically improves sampling efficiency.
The algorithm combines local updates in Fourier space with rejection-free
cluster updates which exploit the symmetries of the Josephson coupling energy.
As an application, we consider the localization transition of a single junction
at intermediate Josephson coupling and determine the temperature dependence of
the zero bias resistance as a function of dissipation strength.Comment: 4 page
Adjoint master equation for multi-time correlators
The quantum regression theorem is a powerful tool for calculating the
muli-time correlators of operators of open quantum systems which dynamics can
be described in Markovian approximation. It enables to obtain the closed system
of equation for the multi-time correlators. However, the scope of the quantum
regression theorem is limited by a particular time order of the operators in
multi-time correlators and does not include out-of-time-ordered correlators. In
this work, we obtain an adjoint master equation for multi-time correlators that
is applicable to out-of-time-ordered correlators. We show that this equation
can be derived for various approaches to description of the dynamics of open
quantum systems, such as the global or local approach. We show that the adjoint
master equation for multi-time correlators is self-consistent. Namely, the
final equation does not depend on how the operators are grouped inside the
correlator, and it coincides with the quantum regression theorem for the
particular time ordering of the operators.Comment: 11 page
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