4,199 research outputs found
Finite-element ray tracing
The interesting acoustic modeling problems often push the practical limits of full-wave models. For instance, in acoustic tomography one needs to be able to predict the propagation of an acoustic pulse for successive realizations of 31) environments. For these types of problems ray methods continue to be attractive because of their speed. Unfortunately, existing codes are prone to a number of implementation difficulties which often degrade their accuracy.
As a result most ray models are actually incapable of producing the ray theoretic result. We discuss a. new method for implementing ray theory that uses a. finite-clement formulation. This method is free of artifacts affecting standard ray models and provides excellent agreement with more computationally intensive full-wave models
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
Could be a molecular state?
We investigate whether the newly observed narrow resonance can
be described as a molecular state with quantum numbers
. Using QCD sum rules, we consider contributions up to dimension
six in the operator product expansion and work at leading order of
. The mass obtained for this state is (4.05\pm 0.28) \mbox{GeV}.
It is concluded that molecular state is a possible candidate
for .Comment: 7 pages, 4 figures.Published in Eur.Phys.J. C73 (2013) 2661. arXiv
admin note: text overlap with arXiv:1304.185
Higher order light-cone distribution amplitudes of the Lambda baryon
The improved light-cone distribution amplitudes (LCDAs) of the
baryon are examined on the basis of the QCD conformal partial wave expansion
approach. The calculations are carried out to the next-to-leading order of
conformal spin accuracy with consideration of twist 6. The next leading order
conformal expansion coefficients are related to the nonperturbative parameters
defined by the local three quark operator matrix elements with different
Lorentz structures with a covariant derivative. The nonperturbative parameters
are determined with the QCD sum rule method. The explicit expressions of the
LCDAs are provided as the main results.Comment: 17pages,10figures. arXiv admin note: text overlap with
arXiv:1311.596
Quantum Signatures of Topological Phase in Bosonic Quadratic System
Quantum entanglement and classical topology are two distinct phenomena that
are difficult to be connected together. Here we discover that an open bosonic
quadratic chain exhibits topology-induced entanglement effect. When the system
is in the topological phase, the edge modes can be entangled in the steady
state, while no entanglement appears in the trivial phase. This finding is
verified through the covariance approach based on the quantum master equations,
which provide exact numerical results without truncation process. We also
obtain concise approximate analytical results through the quantum Langevin
equations, which perfectly agree with the exact numerical results. We show the
topological edge states exhibit near-zero eigenenergies located in the band gap
and are separated from the bulk eigenenergies, which match the
system-environment coupling (denoted by the dissipation rate) and thus the
squeezing correlations can be enhanced. Our work reveals that the stationary
entanglement can be a quantum signature of the topological phase in bosonic
systems, and inversely the topological quadratic systems can be powerful
platforms to generate robust entanglement.Comment: 14 pages, 7 figure
- …