511 research outputs found
Phase estimation with photon number constraint
Many researches proposed the use of the noon state as the input state for
phase estimation, which is one topic of quantum metrology. This is because the
input noon state provides the maximum Fisher information at the specific point.
However, the Fisher information does not necessarily give the attainable bound
for estimation error. In this paper, we adopt the local asymptotic mini-max
criterion as well as the mini-max criterion, and show that the maximum Fisher
information does not give the attainable bound for estimation error under these
criteria in the phase estimation. We also propose the optimal input state under
the constraints for photon number of the input state instead of the noon state.Comment: Several typos are fixed. New section "ANALYSIS ON NOON STATE" is
adde
Parabolic isometries of CAT(0) spaces and CAT(0) dimensions
We study discrete groups from the view point of a dimension gap in connection
to CAT(0) geometry. Developing studies by Brady-Crisp and Bridson, we show that
there exist finitely presented groups of geometric dimension 2 which do not act
properly on any proper CAT(0) spaces of dimension 2 by isometries, although
such actions exist on CAT(0) spaces of dimension 3.
Another example is the fundamental group, G, of a complete, non-compact,
complex hyperbolic manifold M with finite volume, of complex-dimension n > 1.
The group G is acting on the universal cover of M, which is isometric to H^n_C.
It is a CAT(-1) space of dimension 2n. The geometric dimension of G is 2n-1. We
show that G does not act on any proper CAT(0) space of dimension 2n-1 properly
by isometries.
We also discuss the fundamental groups of a torus bundle over a circle, and
solvable Baumslag-Solitar groups.Comment: Published by Algebraic and Geometric Topology at
http://www.maths.warwick.ac.uk/agt/AGTVol4/agt-4-38.abs.htm
Capture of Electroweak Multiplet Dark Matter in Neutron Stars
If dark matter has a sizable scattering cross section with nucleons, it can
efficiently be captured by a neutron star. Its energy is then transferred to
the neutron star as heat through the scattering and annihilation inside the
star. This heating effect may be detectable via dedicated temperature
observations of nearby old pulsars, providing an alternative method for dark
matter searches. In this paper, we show that for electroweak multiplet dark
matter this search strategy can probe the parameter region which is out of
reach of future dark matter direct detection experiments. To see this
systematically, we classify such dark matter candidates in terms of their
electroweak charges and investigate the effect of ultraviolet physics by means
of higher-dimensional effective operators. We then show that if the effect of
ultraviolet physics is sizable, the dark matter-nucleon elastic scattering
cross section becomes sufficiently large, whilst if it is suppressed, then the
mass splittings among the components of the DM multiplet get small enough so
that the inelastic scattering processes are operative. In any case, the
electroweak multiplet dark matter particles are efficiently captured in neutron
stars, making the search strategy with the temperature observation of old
neutron stars promising.Comment: 33 pages, 7 figures, 1 tabl
Vortex Creep Heating vs. Dark Matter Heating in Neutron Stars
Dark matter particles captured in neutron stars deposit their energy as heat.
This DM heating effect can be observed only if it dominates over other internal
heating effects in NSs. In this work, as an example of such an internal heating
source, we consider the frictional heating caused by the creep motion of
neutron superfluid vortex lines in the NS crust. The luminosity of this heating
effect is controlled by the strength of the interaction between the vortex
lines and nuclei in the crust, which can be estimated from the many-body
calculation of a high-density nuclear system as well as through the temperature
observation of old NSs. We show that both the temperature observation and
theoretical calculation suggest that the vortex creep heating dominates over
the DM heating. The vortex-nuclei interaction must be smaller than the
estimated values by several orders of magnitude to overturn this.Comment: 8 pages, 2 figure
Comparison between the Cramer-Rao and the mini-max approaches in quantum channel estimation
In a unified viewpoint in quantum channel estimation, we compare the
Cramer-Rao and the mini-max approaches, which gives the Bayesian bound in the
group covariant model. For this purpose, we introduce the local asymptotic
mini-max bound, whose maximum is shown to be equal to the asymptotic limit of
the mini-max bound. It is shown that the local asymptotic mini-max bound is
strictly larger than the Cramer-Rao bound in the phase estimation case while
the both bounds coincide when the minimum mean square error decreases with the
order O(1/n). We also derive a sufficient condition for that the minimum mean
square error decreases with the order O(1/n).Comment: In this revision, some unlcear parts are clarifie
Perturbation Analysis of Superconductivity in the Trellis-Lattice Hubbard Model
We investigate pairing symmetry and transition temperature in the
trellis-lattice Hubbard model. We solve the \'Eliashberg equation using the
third-order perturbation theory with respect to the on-site repulsion . We
find that a spin-singlet state is very stable in a wide range of parameters. On
the other hand, when the electron number density is shifted from the
half-filled state and the band gap between two bands is small, a spin-triplet
superconductivity is expected. Finally, we discuss a possibility of
unconventional superconductivity and pairing symmetry in
SrCaCuO.Comment: 7pages, 10 figures. To be published in J. Phys. Soc. Jp
Otimizaçâo das condições de preparação de eletrodos à base de carbono cerâmico utilizando-se planejamento fatorial
Different parameters of carbon ceramic electrodes (CCE) preparation, such as type of precursor, carbon material, catalyst amount, among others, significantly influence the morphological properties and consequently their electrochemical responses. This paper describes a 2³ factorial design (2 factors and 3 levels with central point replicates), which the factors analyzed were catalyst amount (HCl 12 mol L-1), graphite/precursor ratio, and precursor type (TEOS - tetraethoxysilane and MTMOS - methyltrimetoxysilane). The design resulted in a significant third order interaction for peak current values (Ipa) and a second order interaction for potential difference (ΔE), between thefactors studied, which could not be observed when using an univariated study
Charge-Density-Wave Formation in the Doped Two-Leg Extended Hubbard Ladder
We investigate electronic properties of the doped two-leg Hubbard ladder with
both the onsite and the nearest-neighbor Coulomb repulsions, by using the the
weak-coupling renormalization-group method. It is shown that, for strong
nearest-neighbor repulsions, the charge-density-wave state coexisting with the
p-density-wave state becomes dominant fluctuation where spins form intrachain
singlets. By increasing doping rate, we have also shown that the effects of the
nearest-neighbor repulsions are reduced and the system exhibits a quantum phase
transition into the d-wave-like (or rung-singlet) superconducting state. We
derive the effective fermion theory which describes the critical properties of
the transition point with the gapless excitation of magnon. The phase diagram
of the two-leg ladder compound, Sr_{14-x}Ca_xCu_{24}O_{41}, is discussed.Comment: 4 pages, 2 figure
Relative Riemann-Zariski spaces
In this paper we study relative Riemann-Zariski spaces attached to a morphism
of schemes and generalizing the classical Riemann-Zariski space of a field. We
prove that similarly to the classical RZ spaces, the relative ones can be
described either as projective limits of schemes in the category of locally
ringed spaces or as certain spaces of valuations. We apply these spaces to
prove the following two new results: a strong version of stable modification
theorem for relative curves; a decomposition theorem which asserts that any
separated morphism between quasi-compact and quasi-separated schemes factors as
a composition of an affine morphism and a proper morphism. (In particular, we
obtain a new proof of Nagata's compactification theorem.)Comment: 30 pages, the final version, to appear in Israel J. of Mat
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