8,174 research outputs found
A universal gap for non-spin quantum control systems
We prove the existence of a universal gap for minimum time controllability of
finite dimensional quantum systems, except for some basic representations of
spin groups.
This is equivalent to the existence of a gap in the diameter of orbit spaces
of the corresponding compact connected Lie group unitary actions on the
Hermitian spheres
Approximate Controllability, Exact Controllability, and Conical Eigenvalue Intersections for Quantum Mechanical Systems
International audienceWe study the controllability of a closed control-affine quantum system driven by two or more external fields. We provide a sufficient condition for controllability in terms of existence of conical intersections between eigenvalues of the Hamiltonian in dependence of the controls seen as parameters. Such spectral condition is structurally stable in the case of three controls or in the case of two controls when the Hamiltonian is real. The spectral condition appears naturally in the adiabatic control framework and yields approximate controllability in the infinite-dimensional case. In the finite-dimensional case it implies that the system is Lie-bracket generating when lifted to the group of unitary transformations, and in particular that it is exactly controllable. Hence, Lie algebraic conditions are deduced from purely spectral properties. We conclude the article by proving that approximate and exact controllability are equivalent properties for general finite-dimensional quantum systems
Sentiment and behaviour annotation in a corpus of dialogue summaries
This paper proposes a scheme for sentiment annotation. We show how the task can be made tractable by focusing on one of the many aspects of sentiment: sentiment as it is recorded in behaviour reports of people and their interactions. Together with a number of measures for supporting the reliable application of the scheme, this allows us to obtain sufficient to good agreement scores (in terms of Krippendorf's alpha) on three key dimensions: polarity, evaluated party and type of clause. Evaluation of the scheme is carried out through the annotation of an existing corpus of dialogue summaries (in English and Portuguese) by nine annotators. Our contribution to the field is twofold: (i) a reliable multi-dimensional annotation scheme for sentiment in behaviour reports; and (ii) an annotated corpus that was used for testing the reliability of the scheme and which is made available to the research community
Kohn-Sham decomposition in real-time time-dependent density-functional theory: An efficient tool for analyzing plasmonic excitations
The real-time-propagation formulation of time-dependent density-functional
theory (RT-TDDFT) is an efficient method for modeling the optical response of
molecules and nanoparticles. Compared to the widely adopted linear-response
TDDFT approaches based on, e.g., the Casida equations, RT-TDDFT appears,
however, lacking efficient analysis methods. This applies in particular to a
decomposition of the response in the basis of the underlying single-electron
states. In this work, we overcome this limitation by developing an analysis
method for obtaining the Kohn-Sham electron-hole decomposition in RT-TDDFT. We
demonstrate the equivalence between the developed method and the Casida
approach by a benchmark on small benzene derivatives. Then, we use the method
for analyzing the plasmonic response of icosahedral silver nanoparticles up to
Ag. Based on the analysis, we conclude that in small nanoparticles
individual single-electron transitions can split the plasmon into multiple
resonances due to strong single-electron-plasmon coupling whereas in larger
nanoparticles a distinct plasmon resonance is formed.Comment: 11 pages, 3 figure
Prospects for detection of detached double white dwarf binaries with Gaia, LSST and LISA
Double white dwarf (DWD) binaries are expected to be very common in the Milky
Way, but their intrinsic faintness challenges the detection of these systems.
Currently, only a few tens of detached DWDs are know. Such systems offer the
best chance of extracting the physical properties that would allow us to
address a wealth of outstanding questions ranging from the nature of white
dwarfs, over stellar and binary evolution to mapping the Galaxy. In this paper
we explore the prospects for detections of ultra-compact (with binary
separations of a few solar radii or less) detached DWDs in: 1) optical
radiation with Gaia and the LSST and 2) gravitational wave radiation with LISA.
We show that Gaia, LSST and LISA have the potential to detect respectively
around a few hundreds, a thousand, and 25 thousand DWD systems. Moreover, Gaia
and LSST data will extend by respectively a factor of two and seven the
guaranteed sample of binaries detected in electromagnetic and gravitational
wave radiation, opening the era of multi-messenger astronomy for these sources.Comment: submitted to MNRA
Propagation of chaos and hydrodynamic description for topological models
In this work, we study the deterministic Cucker-Smale model with topological
interaction.Focusing on the solutions of the corresponding Liouville equation,
we show that propagation of chaos holds.Moreover, by looking at the monokinetic
solutions, we also obtain a rigorous derivation of the hydrodynamic description
given by a pressureless Euler-type system
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