5,814 research outputs found
Excited states of holographic superconductors
In this paper we re-investigate the model of the anti-de Sitter gravity
coupled to Maxwell and charged scalar fields, which has been studied as the
gravitational dual to a superconductor for a long time since the famous work
[Phys.\ Rev.\ Lett.\ {\bf 101}, 031601 (2008)]. By numerical method, we present
a novel family of solutions of holographical superconductor with excited
states, and find there exists a lower critical temperature in the corresponding
excited state. Moreover, we study the condensate and conductivity in the
excited states. It is very interesting that the conductivity of each
excited state has an additional pole in and a delta
function in arising at the low temperature inside the gap,
which is just the evidence of the existence of excited states.Comment: 13 pages, 3 figures; V2: discussions and references added, accepted
for publication in JHE
Flag Additivity in Quantum Resource Theories
Quantum resource theories offer a powerful framework for studying various
phenomena in quantum physics. Despite considerable effort has been devoted to
developing a unified framework of resource theories, there are few common
properties that hold for all quantum resources. In this paper, we fill this gap
by introducing the flag additivity based on the tensor product structure and
the flag basis for the general quantum resources. To illustrate the usefulness
of flag additivity, we show that flag additivity can be used to derive other
nontrivial properties in quantum resource theories, e.g., strong monotonicity,
convexity, and full additivity.Comment: 6 page
Dual Iterative Hard Thresholding: From Non-convex Sparse Minimization to Non-smooth Concave Maximization
Iterative Hard Thresholding (IHT) is a class of projected gradient descent
methods for optimizing sparsity-constrained minimization models, with the best
known efficiency and scalability in practice. As far as we know, the existing
IHT-style methods are designed for sparse minimization in primal form. It
remains open to explore duality theory and algorithms in such a non-convex and
NP-hard problem setting. In this paper, we bridge this gap by establishing a
duality theory for sparsity-constrained minimization with -regularized
loss function and proposing an IHT-style algorithm for dual maximization. Our
sparse duality theory provides a set of sufficient and necessary conditions
under which the original NP-hard/non-convex problem can be equivalently solved
in a dual formulation. The proposed dual IHT algorithm is a super-gradient
method for maximizing the non-smooth dual objective. An interesting finding is
that the sparse recovery performance of dual IHT is invariant to the Restricted
Isometry Property (RIP), which is required by virtually all the existing primal
IHT algorithms without sparsity relaxation. Moreover, a stochastic variant of
dual IHT is proposed for large-scale stochastic optimization. Numerical results
demonstrate the superiority of dual IHT algorithms to the state-of-the-art
primal IHT-style algorithms in model estimation accuracy and computational
efficiency
Enhanced absorption of monolayer MoS2 with resonant back reflector
By extracting the permittivity of monolayer MoS2 from experiments, the
optical absorption of monolayer MoS2 prepared on top of one-dimensional
photonic crystal (1DPC) or metal films is investigated theoretically. The 1DPC
and metal films act as resonant back reflectors that can enhance absorption of
monolayer MoS2 substantially over a broad spectral range due to the Fabry-Perot
cavity effect. The absorption of monolayer MoS2 can also be tuned by varying
either the distance between the monolayer MoS2 and the back reflector or the
thickness of the cover layers.Comment: 4 pages, 3 figure
Self-gravity in neutrino-dominated accretion disks
We present the effects of the self-gravity on the vertical structure and
neutrino luminosity of the neutrino-dominated accretion disks in cylindrical
coordinates. It is found that significant changes of the structure appear in
the outer region of the disk, especially for high accretion rates (e.g., \ga 1
M_\odot~\rm s^{-1}), and thus causes the slight increase of the neutrino
luminosity. Furthermore, the gravitational instability of the disk is reviewed
by the vertical distribution of the Toomre parameter \citep{Toomre1964}, which
may account for the late-time flares in gamma-ray bursts and the extended
emission in short-duration gamma-ray bursts.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Measure-Independent Freezing of Quantum Coherence
We find that all measures of coherence are frozen for an initial state in a
strictly incoherent channel if and only if the relative entropy of coherence is
frozen for the state. Our finding reveals the existence of measure-independent
freezing of coherence, and provides an entropy-based dynamical condition in
which the coherence of an open quantum system is totally unaffected by noise.Comment: 5 pages, no figures, accepted by Physical Review A as Rapid
Communicatio
Estimating coherence measures from limited experimental data available
Quantifying coherence has received increasing attention, and considerable
work has been directed towards finding coherence measures. While various
coherence measures have been proposed in theory, an important issue following
is how to estimate these coherence measures in experiments. This is a
challenging task, since the state of a system is often unknown in practical
applications and the accessible measurements in a real experiment are typically
limited. In this Letter, we put forward an approach to estimate coherence
measures of an unknown state from any limited experimental data available. Our
approach is not only applicable to coherence measures but can be extended to
other resource measures.Comment: 7 pages, 2 figure
Ordering states with coherence measures
The quantification of quantum coherence has attracted a growing attention,
and based on various physical contexts, several coherence measures have been
put forward. An interesting question is whether these coherence measures give
the same ordering when they are used to quantify the coherence of quantum
states. In this paper, we consider the two well-known coherence measures, the
norm of coherence and the relative entropy of coherence, to show that
there are the states for which the two measures give a different ordering. Our
analysis can be extended to other coherence measures, and as an illustration of
the extension we further consider the formation of coherence to show that the
norm of coherence and the formation of coherence, as well as the relative
entropy of coherence and the coherence of formation, do not give the same
ordering too.Comment: 7 pages, 1 figur
A method to constrain mass and spin of GRB black hole within the NDAF model
Black holes (BHs) hide themselves behind various astronomical phenomena, and
their properties, i.e., mass and spin, are usually difficult to constrain. One
leading candidate for the central engine model of gamma-ray bursts (GRBs)
invokes a stellar mass BH and a neutrino-dominated accretion flow (NDAF), with
the relativistic jet launched due to neutrino-anti-neutrino annihilations. Such
a model gives rise to a matter-dominated fireball, and is suitable to interpret
GRBs with a dominant thermal component with a photospheric origin. We propose a
method to constrain BH mass and spin within the framework of this model, and
apply the method to a thermally-dominant GRB 101219B whose initial jet
launching radius is constrained from the data. Using our numerical model
of NDAF jets, we estimate the following constraints on the central BH: mass
, spin parameter , and disk mass
. Our results also suggest
that the NDAF model is a competitive candidate for the central engine of GRBs
with a strong thermal component.Comment: 5 pages, 3 figures, accepted for publication in Ap
A possible feedback mechanism of outflows from a black hole hyperaccretion disk in the center of jet-driven iPTF14hls
iPTF14hls is an unusually bright, long-lived II-P supernova (SN), whose light
curve has at least five peaks. We propose that the outflows from the black hole
hyperaccretion systems in the center of the collapsars should continuously
inject into the envelope. For a jet-driven core-collapsar model, the outflow
feedback results in prolonging the accretion timescale and fluctuating
accretion rates in our analytic solutions. Thus, the long period of luminous,
varying SN iPTF14hls might originate from the choked jets, which are regulated
by the feedback of the strong disk outflows in a massive core-collapsar. One
can expect that jet-driven iPTF14hls may last no more than approximately 3,000
days, and the luminosity may quickly decrease in the later stages. Moreover,
the double-peak light curves in some SNe might be explained by the outflow
feedback mechanism.Comment: 15 pages, 2 figures, accepted for publication in Journal of High
Energy Astrophysic
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