7,974 research outputs found
Entanglement of Solitons in the Frenkel-Kontorova Model
We investigate entanglement of solitons in the continuum-limit of the
nonlinear Frenkel-Kontorova chain. We find that the entanglement of solitons
manifests particle-like behavior as they are characterized by localization of
entanglement. The von-Neumann entropy of solitons mixes critical with
noncritical behaviors. Inside the core of the soliton the logarithmic increase
of the entropy is faster than the universal increase of a critical field,
whereas outside the core the entropy decreases and saturates the constant value
of the corresponding massive noncritical field. In addition, two solitons
manifest long-range entanglement that decreases with the separation of the
solitons more slowly than the universal decrease of the critical field.
Interestingly, in the noncritical regime of the Frenkel-Kontorova model,
entanglement can even increase with the separation of the solitons. We show
that most of the entanglement of the so-called internal modes of the solitons
is saturated by local degrees of freedom inside the core, and therefore we
suggest using the internal modes as carriers of quantum information.Comment: 16 pages, 22 figure
Gauge Fixing and Scattering Amplitudes in String Field Theory Expanded around Universal Solutions
We study a gauge fixed action of open string field theory expanded around the
universal solution which has been found as an analytic classical solution with
one parameter a. For a>-1/2, we are able to reproduce open string scattering
amplitudes in the theory fixed in the Siegel gauge. At a=-1/2, all scattering
amplitudes vanish and there is no open string excitation in the gauge fixed
theory. These results support the conjecture that the universal solution can be
regarded as pure gauge or the tachyon vacuum solution.Comment: 23 pages, LaTeX with PTPTeX.cls, 1 eps figure. minor corrections,
published versio
Two dimensional black-hole as a topological coset model of c=1 string theory
We show that a special superconformal coset (with ) is equivalent
to matter coupled to two dimensional gravity. This identification allows
a direct computation of the correlation functions of the non-critical
string to all genus, and at nonzero cosmological constant, directly from the
continuum approach. The results agree with those of the matrix model. Moreover
we connect our coset with a twisted version of a Euclidean two dimensional
black hole, in which the ghost and matter systems are mixed.Comment: 51 pages. Appendix by E. Frenke
(In)commensurability, scaling and multiplicity of friction in nanocrystals and application to gold nanocrystals on graphite
The scaling of friction with the contact size and (in)commensurabilty of
nanoscopic and mesoscopic crystals on a regular substrate are investigated
analytically for triangular nanocrystals on hexagonal substrates. The crystals
are assumed to be stiff, but not completely rigid. Commensurate and
incommensurate configurations are identified systematically. It is shown that
three distinct friction branches coexist, an incommensurate one that does not
scale with the contact size () and two commensurate ones which scale
differently (with and ) and are associated with various
combinations of commensurate and incommensurate lattice parameters and
orientations. This coexistence is a direct consequence of the two-dimensional
nature of the contact layer, and such multiplicity exists in all geometries
consisting of regular lattices. To demonstrate this, the procedure is repeated
for rectangular geometry. The scaling of irregularly shaped crystals is also
considered, and again three branches are found (). Based
on the scaling properties, a quantity is defined which can be used to classify
commensurability in infinite as well as finite contacts. Finally, the
consequences for friction experiments on gold nanocrystals on graphite are
discussed
Reaction rate calculation by parallel path swapping
The efficiency of path sampling simulations can be improved considerably
using the approach of path swapping. For this purpose, we have devised a new
algorithmic procedure based on the transition interface sampling technique. In
the same spirit of parallel tempering, paths between different ensembles are
swapped, but the role of temperature is here played by the interface position.
We have tested the method on the denaturation transition of DNA using the
Peyrard-Bishop-Dauxois model. We find that the new algorithm gives a reduction
of the computational cost by a factor 20.Comment: 5 pages, 3 figure
Escorted Free Energy Simulations: Improving Convergence by Reducing Dissipation
Nonequilibrium, ``fast switching'' estimates of equilibrium free energy
differences, Delta F, are often plagued by poor convergence due to dissipation.
We propose a method to improve these estimates by generating trajectories with
reduced dissipation. Introducing an artificial flow field that couples the
system coordinates to the external parameter driving the simulation, we derive
an identity for Delta F in terms of the resulting trajectories. When the flow
field effectively escorts the system along a near-equilibrium path, the free
energy estimate converges efficiently and accurately. We illustrate our method
on a model system, and discuss the general applicability of our approach.Comment: 4 pages, including 2 figures, accepted for publication in Phys Rev
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Devil's staircase of incompressible electron states in a nanotube
It is shown that a periodic potential applied to a nanotube can lock
electrons into incompressible states. Depending on whether electrons are weakly
or tightly bound to the potential, excitation gaps open up either due to the
Bragg diffraction enhanced by the Tomonaga - Luttinger correlations, or via
pinning of the Wigner crystal. Incompressible states can be detected in a
Thouless pump setup, in which a slowly moving periodic potential induces
quantized current, with a possibility to pump on average a fraction of an
electron per cycle as a result of interactions.Comment: 4 pages, 1 figure, published versio
A general theory of DNA-mediated and other valence-limited interactions
We present a general theory for predicting the interaction potentials between
DNA-coated colloids, and more broadly, any particles that interact via
valence-limited ligand-receptor binding. Our theory correctly incorporates the
configurational and combinatorial entropic factors that play a key role in
valence-limited interactions. By rigorously enforcing self-consistency, it
achieves near-quantitative accuracy with respect to detailed Monte Carlo
calculations. With suitable approximations and in particular geometries, our
theory reduces to previous successful treatments, which are now united in a
common and extensible framework. We expect our tools to be useful to other
researchers investigating ligand-mediated interactions. A complete and
well-documented Python implementation is freely available at
http://github.com/patvarilly/DNACC .Comment: 18 pages, 10 figure
The 3-graviton vertex function in thermal quantum gravity
The high temperature limit of the 3-graviton vertex function is studied in
thermal quantum gravity, to one loop order. The leading () contributions
arising from internal gravitons are calculated and shown to be twice the ones
associated with internal scalar particles, in correspondence with the two
helicity states of the graviton. The gauge invariance of this result follows in
consequence of the Ward and Weyl identities obeyed by the thermal loops, which
are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100
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