15,037 research outputs found
Controllable Fano resonance and fast to slow light in a hybrid semiconductor/superconductor ring device mediated by Majorana fermions
We demonstrate theoretically the Fano resonance and the conversion from fast
to slow light in a hybrid quantum dot-semiconductor/superconductor ring device,
where the QD is coupled to a pair of MFs appearing in the hybrid S/S ring
device. The absorption spectra of the weak probe field can exhibit a series of
asymmetric Fano line shapes and their related propagation properties such as
fast and slow light effects are investigated based on the hybrid system for
suitable parametric regimes. The positions of the Fano resonances can be
determined by the parameters, such as different detuning regimes and QD-MFs
coupling strengths. Further, the transparency windows (the absorption dip
approaches zero) in the probe absorption spectra are accompanied by the rapid
dispersion, which indicates the slow or fast light effect, and tunable
fast-to-slow light propagation (or vice versa) can be achieved by controlling
different parameter regimes. Our study may provide an all-optical means to
investigate MFs and open up promising applications in quantum information
processing based on MFs in solid state devices
Randomized Algorithms for Large-scale Inverse Problems with General Regularizations
We shall investigate randomized algorithms for solving large-scale linear
inverse problems with general regularizations. We first present some techniques
to transform inverse problems of general form into the ones of standard form,
then apply randomized algorithms to reduce large-scale systems of standard form
to much smaller-scale systems and seek their regularized solutions in
combination with some popular choice rules for regularization parameters. Then
we will propose a second approach to solve large-scale ill-posed systems with
general regularizations. This involves a new randomized generalized SVD
algorithm that can essentially reduce the size of the original large-scale
ill-posed systems. The reduced systems can provide approximate regularized
solutions with about the same accuracy as the ones by the classical generalized
SVD, and more importantly, the new approach gains obvious robustness, stability
and computational time as it needs only to work on problems of much smaller
size. Numerical results are given to demonstrated the efficiency of the
algorithms
Finite Element Methods For Interface Problems On Local Anisotropic Fitting Mixed Meshes
A simple and efficient interface-fitted mesh generation algorithm is
developed in this paper. This algorithm can produce a local anisotropic fitting
mixed mesh which consists of both triangles and quadrilaterals near the
interface. A new finite element method is proposed for second order elliptic
interface problems based on the resulting mesh. Optimal approximation
capabilities on anisotropic elements are proved in both the and
norms. The discrete system is usually ill-conditioned due to anisotropic and
small elements near the interface. Thereupon, a multigrid method is presented
to handle this issue. The convergence rate of the multigrid method is shown to
be optimal with respect to both the coefficient jump ratio and mesh size.
Numerical experiments are presented to demonstrate the theoretical results
The next-to-leading order corrections to transition in the factorization
In this paper, we investigate the factorization hypothesis step by step for
the exclusive process at next-to-leading order (NLO) with the
collinear factorization approach, and then we extend our results to the
factorization frame. We show that the soft divergence from the specific NLO
diagrams will cancel each other at the quark level, while the remaining
collinear divergence can be absorbed into the NLO wave functions. The full NLO
amplitudes can be factorized into two parts: the NLO and meson wave
functions containing the collinear divergence and the leading order (LO) finite
hard kernels. We give the general form of the nonlocal hadron matrix for the
NLO and meson wave functions and all results of factorization for
different twists' combinations.Comment: 22 pages, 7 figure
Top-quark forward-backward asymmetry in e+e- annihilation at NNLO in QCD
We report on a complete calculation of electroweak production of top quark
pairs in annihilation at next-to-next-to-leading order in Quantum
Chromodynamics. Our setup is fully differential and can be used to calculate
any infrared-safe observable. Especially we calculated the
next-to-next-to-leading order corrections to top-quark forward-backward
asymmetry and found sizable effects. Our results show a large reduction of the
theoretical uncertainties in predictions of the forward-backward asymmetry, and
allow a precision determination of the top quark electroweak couplings at
future colliders.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1408.515
Fast Multi-Instance Multi-Label Learning
In many real-world tasks, particularly those involving data objects with
complicated semantics such as images and texts, one object can be represented
by multiple instances and simultaneously be associated with multiple labels.
Such tasks can be formulated as multi-instance multi-label learning (MIML)
problems, and have been extensively studied during the past few years. Existing
MIML approaches have been found useful in many applications; however, most of
them can only handle moderate-sized data. To efficiently handle large data
sets, in this paper we propose the MIMLfast approach, which first constructs a
low-dimensional subspace shared by all labels, and then trains label specific
linear models to optimize approximated ranking loss via stochastic gradient
descent. Although the MIML problem is complicated, MIMLfast is able to achieve
excellent performance by exploiting label relations with shared space and
discovering sub-concepts for complicated labels. Experiments show that the
performance of MIMLfast is highly competitive to state-of-the-art techniques,
whereas its time cost is much less; particularly, on a data set with 20K bags
and 180K instances, MIMLfast is more than 100 times faster than existing MIML
approaches. On a larger data set where none of existing approaches can return
results in 24 hours, MIMLfast takes only 12 minutes. Moreover, our approach is
able to identify the most representative instance for each label, and thus
providing a chance to understand the relation between input patterns and output
label semantics
Quantum beat phenomenon presence in coherent spin dynamics of spin-2 Rb atoms in a deep optical lattice
Motivated by the recent experimental work (A. Widera, \textit{et al}, Phys.
Rev. Lett. 95, 19045), we study the collisional spin dynamics of two spin-2 Rb atoms confined in a deep optical lattice. When the system is
initialized as , three different two-particle Zeeman states are involved
in the time evolution due to the conservation of magnetization. For a large
magnetic field Guass, the spin coherent dynamics reduces to a Rabi-like
oscillation between the states and . However, under a small
magnetic field, a general three-level coherent oscillation displays. In
particular, around a critical magnetic field Guass, the
probability in the Zeeman states exhibits a novel quantum beat
phenomenon, ready to be confirmed in future experiments.Comment: 5 pages, 5 figure
Ultrasensitive Detection of Majorana Fermions via Spin-based Optomechanics with Carbon Nanotubes
We propose a novel optical method to detect the existence of Majorana
fermions at the ends of the semiconductor nanowire via the coupling to an
electron spin trapped on a carbon nanotube resonator under the control of a
strong pump field and a weak probe field. The coupling strength of Majorana
fermion to the spin in the carbon nanotube and the decay rate of the Majorana
fermion can be easily measured from the probe absorption spectrum via
manipulating the spin-mechanical coupling in the suspended\ carbon nanotube.
The scheme proposed here will open a good perspective for its applications in
all-optical controlled Majorana fermion-based quantum computation and quantum
information processing
Entropy evolution law in a laser process
For the first time, we obtain the entropy variation law in a laser process
after finding the Kraus operator of the master equation describing the laser
process with the use of the entangled state representation. The behavior of
entropy is determined by the competition of the gain and damping in the laser
process. The photon number evolution formula is also obtained
The transition form factors in the Perturbative QCD factorization approach
In this paper, we studied the and transition processes and made the calculations for the
transition form factor and the meson
electromagnetic form factors, and , by
employing the perturbative QCD (PQCD) factorization approach. For the transition, we found that the contribution to form factor
from the term proportional to the distribution amplitude
combination is absolutely dominant, and
the PQCD predictions for both the size and the -dependence of this form
factor agree well with those from the extended ADS/QCD
models or the light-cone QCD sum rule. For the
transition and in the region of GeV, further more, we found
that the PQCD predictions for the magnitude and their -dependence of the
and form factors agree well with those from the QCD sum
rule, while the PQCD prediction for is much larger than the one from
the QCD sum rule.Comment: 11 pages, 3 figure
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