2,712 research outputs found
Distribution of velocities in an avalanche
For a driven elastic object near depinning, we derive from first principles
the distribution of instantaneous velocities in an avalanche. We prove that
above the upper critical dimension, d >= d_uc, the n-times distribution of the
center-of-mass velocity is equivalent to the prediction from the ABBM
stochastic equation. Our method allows to compute space and time dependence
from an instanton equation. We extend the calculation beyond mean field, to
lowest order in epsilon=d_uc-d.Comment: 4 pages, 2 figure
Height fluctuations of a contact line: a direct measurement of the renormalized disorder correlator
We have measured the center-of-mass fluctuations of the height of a contact
line at depinning for two different systems: liquid hydrogen on a rough cesium
substrate and isopropanol on a silicon wafer grafted with silanized patches.
The contact line is subject to a confining quadratic well, provided by gravity.
From the second cumulant of the height fluctuations, we measure the
renormalized disorder correlator Delta(u), predicted by the Functional RG
theory to attain a fixed point, as soon as the capillary length is large
compared to the Larkin length set by the microscopic disorder. The experiments
are consistent with the asymptotic form for Delta(u) predicted by Functional
RG, including a linear cusp at u=0. The observed small deviations could be used
as a probe of the underlying physical processes. The third moment, as well as
avalanche-size distributions are measured and compared to predictions from
Functional RG.Comment: 6 pages, 14 figure
The (2+1)-d U(1) Quantum Link Model Masquerading as Deconfined Criticality
The -d U(1) quantum link model is a gauge theory, amenable to quantum
simulation, with a spontaneously broken SO(2) symmetry emerging at a quantum
phase transition. Its low-energy physics is described by a -d \RP(1)
effective field theory, perturbed by a dangerously irrelevant SO(2) breaking
operator, which prevents the interpretation of the emergent pseudo-Goldstone
boson as a dual photon. At the quantum phase transition, the model mimics some
features of deconfined quantum criticality, but remains linearly confining.
Deconfinement only sets in at high temperature.Comment: 4.5 pages, 6 figure
Crystalline Confinement
We show that exotic phases arise in generalized lattice gauge theories known
as quantum link models in which classical gauge fields are replaced by quantum
operators. While these quantum models with discrete variables have a
finite-dimensional Hilbert space per link, the continuous gauge symmetry is
still exact. An efficient cluster algorithm is used to study these exotic
phases. The -d system is confining at zero temperature with a
spontaneously broken translation symmetry. A crystalline phase exhibits
confinement via multi-stranded strings between charge-anti-charge pairs. A
phase transition between two distinct confined phases is weakly first order and
has an emergent spontaneously broken approximate global symmetry. The
low-energy physics is described by a -d effective field
theory, perturbed by a dangerously irrelevant breaking operator, which
prevents the interpretation of the emergent pseudo-Goldstone boson as a dual
photon. This model is an ideal candidate to be implemented in quantum
simulators to study phenomena that are not accessible using Monte Carlo
simulations such as the real-time evolution of the confining string and the
real-time dynamics of the pseudo-Goldstone boson.Comment: Proceedings of the 31st International Symposium on Lattice Field
Theory - LATTICE 201
GPRD, A Database for the Spectral Properties of Diatomic Molecules of Atmospheric Interest
A short note describing the development of a database providing factual and
numerical data on the spectral properties of diatomic molecules. This database
is available online for the overall scientific community at the following
adress: http://cfp.ist.utl.pt/radiation/Comment: 2 page
Systematic Effective Field Theory Investigation of Spiral Phases in Hole-Doped Antiferromagnets on the Honeycomb Lattice
Motivated by possible applications to the antiferromagnetic precursor of the
high-temperature superconductor NaCoOyHO, we use a systematic
low-energy effective field theory for magnons and holes to study different
phases of doped antiferromagnets on the honeycomb lattice. The effective action
contains a leading single-derivative term, similar to the Shraiman-Siggia term
in the square lattice case, which gives rise to spirals in the staggered
magnetization. Depending on the values of the low-energy parameters, either a
homogeneous phase with four or a spiral phase with two filled hole pockets is
energetically favored. Unlike in the square lattice case, at leading order the
effective action has an accidental continuous spatial rotation symmetry.
Consequently, the spiral may point in any direction and is not necessarily
aligned with a lattice direction.Comment: 10 pages, 6 figure
Two-dimensional Lattice Gauge Theories with Superconducting Quantum Circuits
A quantum simulator of U(1) lattice gauge theories can be implemented with
superconducting circuits. This allows the investigation of confined and
deconfined phases in quantum link models, and of valence bond solid and spin
liquid phases in quantum dimer models. Fractionalized confining strings and the
real-time dynamics of quantum phase transitions are accessible as well. Here we
show how state-of-the-art superconducting technology allows us to simulate
these phenomena in relatively small circuit lattices. By exploiting the strong
non-linear couplings between quantized excitations emerging when
superconducting qubits are coupled, we show how to engineer gauge invariant
Hamiltonians, including ring-exchange and four-body Ising interactions. We
demonstrate that, despite decoherence and disorder effects, minimal circuit
instances allow us to investigate properties such as the dynamics of electric
flux strings, signaling confinement in gauge invariant field theories. The
experimental realization of these models in larger superconducting circuits
could address open questions beyond current computational capability.Comment: Published versio
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