1,701 research outputs found
Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure
Bundles of many fibers, with statistically distributed thresholds for
breakdown of individual fibers and where the load carried by a bursting fiber
is equally distributed among the surviving members, are considered. During the
breakdown process, avalanches consisting of simultaneous rupture of several
fibers occur, with a distribution D(Delta) of the magnitude Delta of such
avalanches. We show that there is, for certain threshold distributions, a
crossover behavior of D(Delta) between two power laws D(Delta) proportional to
Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic
behavior, and we give the condition for which the D(Delta) proportional to
Delta^(-3/2) behavior is seen. This crossover is a signal of imminent
catastrophic failure in the fiber bundle. We find the same crossover behavior
in the fuse model.Comment: 4 pages, 4 figure
Evidence for Superfluidity in a Resonantly Interacting Fermi Gas
We observe collective oscillations of a trapped, degenerate Fermi gas of
Li atoms at a magnetic field just above a Feshbach resonance, where the
two-body physics does not support a bound state. The gas exhibits a radial
breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the
frequency of Hz predicted for a
{\em hydrodynamic} Fermi gas with unitarity limited interactions. The measured
damping times and frequencies are inconsistent with predictions for both the
collisionless mean field regime and for collisional hydrodynamics. These
observations provide the first evidence for superfluid hydrodynamics in a
resonantly interacting Fermi gas.Comment: 5 pages, ReVTeX4, 2 eps figs. Resubmitted to PRL in response to
referees' comments. Title and abstract changed. Corrected error in Table 1,
atom numbers for 0.33 TF and 0.5 TF data were interchanged. Corrected typo in
ref 3. Added new figure of damping time versus temperatur
Strong coupling of single emitters to surface plasmons
We propose a method that enables strong, coherent coupling between individual
optical emitters and electromagnetic excitations in conducting nano-structures.
The excitations are optical plasmons that can be localized to sub-wavelength
dimensions. Under realistic conditions, the tight confinement causes optical
emission to be almost entirely directed into the propagating plasmon modes via
a mechanism analogous to cavity quantum electrodynamics. We first illustrate
this result for the case of a nanowire, before considering the optimized
geometry of a nanotip. We describe an application of this technique involving
efficient single-photon generation on demand, in which the plasmons are
efficiently out-coupled to a dielectric waveguide. Finally we analyze the
effects of increased scattering due to surface roughness on these
nano-structures.Comment: 34 pages, 7 figure
Coherent Population Trapping of Single Spins in Diamond Under Optical Excitation
Coherent population trapping is demonstrated in single nitrogen-vacancy
centers in diamond under optical excitation. For sufficient excitation power,
the fluorescence intensity drops almost to the background level when the laser
modulation frequency matches the 2.88 GHz splitting of the ground states. The
results are well described theoretically by a four-level model, allowing the
relative transition strengths to be determined for individual centers. The
results show that all-optical control of single spins is possible in diamond.Comment: minor correction
Quantum Optics with Surface Plasmons
We describe a technique that enables strong, coherent coupling between
individual optical emitters and guided plasmon excitations in conducting
nano-structures at optical frequencies. We show that under realistic
conditions, optical emission can be almost entirely directed into the plasmon
modes. As an example, we describe an application of this technique involving
efficient generation of single photons on demand, in which the plasmon is
efficiently out-coupled to a dielectric waveguide.Comment: 11 pages, 3 figure
Phase transition in the modified fiber bundle model
We extend the standard fiber bundle model (FBM) with the local load sharing
in such a way that the conservation of the total load is relaxed when an
isolated fiber is broken. In this modified FBM in one dimension (1D), it is
revealed that the model exhibits a well-defined phase transition at a finite
nonzero value of the load, which is in contrast to the standard 1D FBM. The
modified FBM defined in the Watts-Strogatz network is also investigated, and
found is the existences of two distinct transitions: one discontinuous and the
other continuous. The effects of the long-range shortcuts are also discussed.Comment: 7 pages, to appear in Europhys. Let
Enhanced Nonlinear Generation in a Three-Level Medium with Spatially Dependent Coherence
We consider a method for efficient parametric generation of a laser pulse. A
single laser field is injected to a three-level medium which has two lower
states and one excited state. The lower states are prepared initially in a
position-dependent coherent superposition state. It is shown that by proper
choice of the position dependence of the superposition along the direction of
propagation, the incoming field can be converted completely to a new field.Comment: Revtex4 document, 3 pages, 2 figure
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