54,523 research outputs found
Metric adjusted skew information
We extend the concept of Wigner-Yanase-Dyson skew information to something we
call ``metric adjusted skew information'' (of a state with respect to a
conserved observable). This ``skew information'' is intended to be a
non-negative quantity bounded by the variance (of an observable in a state)
that vanishes for observables commuting with the state. We show that the skew
information is a convex function on the manifold of states. It also satisfies
other requirements, proposed by Wigner and Yanase, for an effective
measure-of-information content of a state relative to a conserved observable.
We establish a connection between the geometrical formulation of quantum
statistics as proposed by Chentsov and Morozova and measures of quantum
information as introduced by Wigner and Yanase and extended in this article. We
show that the set of normalized Morozova-Chentsov functions describing the
possible quantum statistics is a Bauer simplex and determine its extreme
points. We determine a particularly simple skew information, the ``lambda-skew
information,'' parametrized by a lambda in (0,1], and show that the convex cone
this family generates coincides with the set of all metric adjusted skew
informations.
Key words: Skew information, convexity, monotone metric, Morozova-Chentsov
function, lambda-skew information.Comment: Edited the abstract and the introductio
Inequalities for quantum skew information
We study quantum information inequalities and show that the basic inequality
between the quantum variance and the metric adjusted skew information generates
all the multi-operator matrix inequalities or Robertson type determinant
inequalities studied by a number of authors. We introduce an order relation on
the set of functions representing quantum Fisher information that renders the
set into a lattice with an involution. This order structure generates new
inequalities for the metric adjusted skew informations. In particular, the
Wigner-Yanase skew information is the maximal skew information with respect to
this order structure in the set of Wigner-Yanase-Dyson skew informations.
Key words and phrases: Quantum covariance, metric adjusted skew information,
Robertson-type uncertainty principle, operator monotone function,
Wigner-Yanase-Dyson skew information
Spherical geometry and integrable systems
We prove that the cosine law for spherical triangles and spherical tetrahedra
defines integrable systems, both in the sense of multidimensional consistency
and in the sense of dynamical systems.Comment: 15 pages, 5 figure
Metric adjusted skew information: Convexity and restricted forms of superadditivity
We give a truly elementary proof of the convexity of metric adjusted skew
information following an idea of Effros. We extend earlier results of weak
forms of superadditivity to general metric adjusted skew informations.
Recently, Luo and Zhang introduced the notion of semi-quantum states on a
bipartite system and proved superadditivity of the Wigner-Yanase-Dyson skew
informations for such states. We extend this result to general metric adjusted
skew informations. We finally show that a recently introduced extension to
parameter values of the WYD-information is a special case of
(unbounded) metric adjusted skew information.Comment: An error in the literature is pointed ou
The Range of Validity for the Kelvin Force
In a recent Letter, Luo, Du and Huang reported a novel convective instability
driven by a force rarely studied before -- that exerted by an external magnetic
field on a strongly magnetizable liquid. The associated physics is surprisingly
rich and promises many more interesting results for the future. Unfortunately,
the analysis starts from a misconception and employs the Kelvin force outside
its range of validity. Since few would recognize this as a mistake, and since
its consequence in the given experiment is particularly direct and critical,
this is a point well worth being clarified, and clearly understood.Comment: 1 pag
Mixed-Spin Pairing Condensates in Heavy Nuclei
We show that the Bogoliubov-de Gennes equations for nuclear ground-state wave
functions support solutions in which the condensate has a mixture of
spin-singlet and spin-triplet pairing. We find that such mixed-spin condensates
do not occur when there are equal numbers of neutrons and protons, but only
when there is an isospin imbalance. Using a phenomenological Hamiltonian, we
predict that such nuclei may occur in the physical region within the proton
dripline. We also solve the Bogoliubov-de Gennes equations with variable
constraints on the spin-singlet and spin-triplet pairing amplitudes. For nuclei
that exhibit this new pairing behavior, the resulting energy surface can be
rather soft, suggesting that there may be low-lying excitations associated with
the spin mixing.Comment: 4+ pages, 3 figures, 1 table; 1 reference added; v2 corresponds to
the published versio
Evaluating single-sided natural ventilation models against full-scale idealised measurements: impact of wind direction and turbulence
Commonly single-sided natural ventilation is used in temperate climates to provide comfortable and healthy indoor environments. However, within built-up areas it is difficult to predict natural ventilation rates for buildings as they depend on many flow factors and opening type. Here, existing models are evaluated using the nine-month Refresh Cube Campaign (RCC). Pressure-based ventilation rates were determined for a small opening (1% porosity) in a cubical test building (side=6 m). The building was isolated and then sheltered in a limited staggered building array to simulate turbulent flows in dense urban areas. Internal and external flow, temperature and pressure measurements captured a wide range of scales of variability. Although the Warren and Parkins (1985, WP85) model performed best for 30-minute mean ventilation rates, all four models tested underestimated ventilation rates by a factor of 10. As wind dominated the stack effect, new coefficients were derived for the WP85 wind-driven model as a function of wind angle. Predictions were mostly improved, except for directions with complex flow patterns during the sheltered case. For the first time, the relation between ventilation rate and turbulence intensity (TI) around a full-scale building was tested. Results indicate that the wind-driven model for single-sided ventilation in highly turbulent flows (0.5<TI<4) can be improved by including TI as a multiplicative factor. Although small window openings with highly turbulent flows are common for sheltered buildings in urban areas, future model development should include a variety of configurations to assess the generality of these results
Observation of a quenched moment of inertia in a rotating strongly interacting Fermi gas
We make a model-independent measurement of the moment of inertia of a
rotating, expanding strongly-interacting Fermi gas. Quenching of the moment of
inertia is observed for energies both below and above the superfluid
transition. This shows that a strongly interacting Fermi gas with angular
momentum can support irrotational flow in both the superfluid and collisional
normal fluid regimes.Comment: 4 pages 5 figure
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