11,347 research outputs found
Quantum key distribution with "dual detectors"
To improve the performance of a quantum key distribution (QKD) system, high
speed, low dark count single photon detectors (or low noise homodyne detectors)
are required. However, in practice, a fast detector is usually noisy. Here, we
propose a "dual detectors" method to improve the performance of a practical QKD
system with realistic detectors: the legitimate receiver randomly uses either a
fast (but noisy) detector or a quiet (but slow) detector to measure the
incoming quantum signals. The measurement results from the quiet detector can
be used to bound eavesdropper's information, while the measurement results from
the fast detector are used to generate secure key. We apply this idea to
various QKD protocols. Simulation results demonstrate significant improvements
in both BB84 protocol with ideal single photon source and Gaussian-modulated
coherent states (GMCS) protocol; while for decoy-state BB84 protocol with weak
coherent source, the improvement is moderate. We also discuss various practical
issues in implementing the "dual detectors" scheme.Comment: 22 pages, 9 figure
A balanced homodyne detector for high-rate Gaussian-modulated coherent-state quantum key distribution
We discuss excess noise contributions of a practical balanced homodyne
detector in Gaussian-modulated coherent-state (GMCS) quantum key distribution
(QKD). We point out the key generated from the original realistic model of GMCS
QKD may not be secure. In our refined realistic model, we take into account
excess noise due to the finite bandwidth of the homodyne detector and the
fluctuation of the local oscillator. A high speed balanced homodyne detector
suitable for GMCS QKD in the telecommunication wavelength region is built and
experimentally tested. The 3dB bandwidth of the balanced homodyne detector is
found to be 104MHz and its electronic noise level is 13dB below the shot noise
at a local oscillator level of 8.5*10^8 photon per pulse. The secure key rate
of a GMCS QKD experiment with this homodyne detector is expected to reach
Mbits/s over a few kilometers.Comment: 22 pages, 11 figure
Security Analysis of an Untrusted Source for Quantum Key Distribution: Passive Approach
We present a passive approach to the security analysis of quantum key
distribution (QKD) with an untrusted source. A complete proof of its
unconditional security is also presented. This scheme has significant
advantages in real-life implementations as it does not require fast optical
switching or a quantum random number generator. The essential idea is to use a
beam splitter to split each input pulse. We show that we can characterize the
source using a cross-estimate technique without active routing of each pulse.
We have derived analytical expressions for the passive estimation scheme.
Moreover, using simulations, we have considered four real-life imperfections:
Additional loss introduced by the "plug & play" structure, inefficiency of the
intensity monitor, noise of the intensity monitor, and statistical fluctuation
introduced by finite data size. Our simulation results show that the passive
estimate of an untrusted source remains useful in practice, despite these four
imperfections. Also, we have performed preliminary experiments, confirming the
utility of our proposal in real-life applications. Our proposal makes it
possible to implement the "plug & play" QKD with the security guaranteed, while
keeping the implementation practical.Comment: 35 pages, 19 figures. Published Versio
The role of drop shape in impact and splash
The impact and splash of liquid drops on solid substrates are ubiquitous in
many important fields. However, previous studies have mainly focused on
spherical drops while the non-spherical situations, such as raindrops, charged
drops, oscillating drops, and drops affected by electromagnetic field, remain
largely unexplored. Using ferrofluid, we realize various drop shapes and
illustrate the fundamental role of shape in impact and splash. Experiments show
that different drop shapes produce large variations in spreading dynamics,
splash onset, and splash amount. However, underlying all these variations we
discover universal mechanisms across various drop shapes: the impact dynamics
is governed by the superellipse model, the splash onset is triggered by the
Kelvin-Helmholtz instability, and the amount of splash is determined by the
energy dissipation before liquid taking off. Our study generalizes the drop
impact research beyond the spherical geometry, and reveals the potential of
using drop shape to control impact and splash.Comment: 14 pages, 4 figure
Poly[[(μ-1H-benzimidazole-5,6-dicarboxylato)zinc(II)] monohydrate]
The three-dimensional polymeric title compound, {[Zn(C9H4N2O4)]·H2O}n, contains one crystallographically independent ZnII atom, one fully deprotonated 1H-benzimidazole-5,6-dicarboxylate (bdc) ligand and one uncoordinated water molecule. The ZnII atom is four-coordinated by three O atoms and one N atom from the bdc ligands, giving a distorted tetrahedral coordination geometry. The uncoordinated water molecule is bound to the main structure through a strong bdc–water N—H⋯O hydrogen bond, and two much weaker water–bdc O—H⋯O interactions
Large Language Models for Software Engineering: A Systematic Literature Review
Large Language Models (LLMs) have significantly impacted numerous domains,
notably including Software Engineering (SE). Nevertheless, a well-rounded
understanding of the application, effects, and possible limitations of LLMs
within SE is still in its early stages. To bridge this gap, our systematic
literature review takes a deep dive into the intersection of LLMs and SE, with
a particular focus on understanding how LLMs can be exploited in SE to optimize
processes and outcomes. Through a comprehensive review approach, we collect and
analyze a total of 229 research papers from 2017 to 2023 to answer four key
research questions (RQs). In RQ1, we categorize and provide a comparative
analysis of different LLMs that have been employed in SE tasks, laying out
their distinctive features and uses. For RQ2, we detail the methods involved in
data collection, preprocessing, and application in this realm, shedding light
on the critical role of robust, well-curated datasets for successful LLM
implementation. RQ3 allows us to examine the specific SE tasks where LLMs have
shown remarkable success, illuminating their practical contributions to the
field. Finally, RQ4 investigates the strategies employed to optimize and
evaluate the performance of LLMs in SE, as well as the common techniques
related to prompt optimization. Armed with insights drawn from addressing the
aforementioned RQs, we sketch a picture of the current state-of-the-art,
pinpointing trends, identifying gaps in existing research, and flagging
promising areas for future study
Multiwavelength VLBI observations of Sagittarius A*
The compact radio source Sgr\,A*, associated with the super massive black
hole at the center of the Galaxy, has been studied with VLBA observations at 3
frequencies (22, 43, 86\,GHz) performed on 10 consecutive days in May 2007. The
total VLBI flux density of Sgr\,A* varies from day to day. The variability is
correlated at the 3 observing frequencies with higher variability amplitudes
appearing at the higher frequencies. For the modulation indices, we find 8.4\,%
at 22\,GHz, 9.3\,% at 43\,GHz, and 15.5\,% at 86\,GHz. The radio spectrum is
inverted between 22 and 86\,GHz, suggesting inhomogeneous synchrotron
self-absorption with a turnover frequency at or above 86\,GHz. The radio
spectral index correlates with the flux density, which is harder (more inverted
spectrum) when the source is brighter. The average source size does not appear
to be variable over the 10-day observing interval. However, we see a tendency
for the sizes of the minor axis to increase with increasing total flux, whereas
the major axis remains constant. Towards higher frequencies, the position angle
of the elliptical Gaussian increases, indicative of intrinsic structure, which
begins to dominate the scatter broadening. At cm-wavelength, the source size
varies with wavelength as , which is interpreted as the
result of interstellar scatter broadening. After removal of this scatter
broadening, the intrinsic source size varies as . The
VLBI closure phases at 22, 43, and 86\,GHz are zero within a few degrees,
indicating a symmetric or point-like source structure. In the context of an
expanding plasmon model, we obtain an upper limit of the expansion velocity of
about 0.1\,c from the non-variable VLBI structure. This agrees with the
velocity range derived from the radiation transport modeling of the flares from
the radio to NIR wavelengths.}Comment: 14pages, 14 Figures, Accepted for publication in A&
2,4-Dihydroxy-N′-(2-hydroxy-4-methoxybenzylidene)benzohydrazide
In the title compound, C15H14N2O5, the dihedral angle between the two benzene rings is 4.3 (3)° and the molecule adopts an E configuration with respect to the C=N bond. Intramolecular O—H⋯N and N—H⋯O hydrogen bonds are observed. In the crystal structure, the molecules are linked through intermolecular N—H⋯O and O—H⋯O hydrogen bonds to form layers parallel to the ac plane
N′-(2,5-Dihydroxybenzylidene)-2-hydroxy-3-methylbenzohydrazide
In the title compound, C15H14N2O4, the dihedral angle between the two benzene rings is 4.1 (2)°. The molecule adopts an E configuration with respect to the C=N bond. There are intramolecular O—H⋯N and O—H⋯O hydrogen bonds in the molecule. In the crystal structure, molecules are linked through intermolecular N—H⋯O and O—H⋯O hydrogen bonds, forming chains running along the c axis
N′-(2-Chlorobenzylidene)-2-hydroxy-3-methylbenzohydrazide
In the title compound, C15H13ClN2O2, the dihedral angle between the two benzene rings is 3.4 (5)° and the molecule adopts an E configuration with respect to the C=N bond. There is an intramolecular O—H⋯O hydrogen bond in the molecule, which generates an S(6) loop. In the crystal structure, molecules are linked through intermolecular N—H⋯O hydrogen bonds, forming C(4) chains running along the a axis
- …