1,046 research outputs found
Asymptotic estimation theory for a finite dimensional pure state model
The optimization of measurement for n samples of pure sates are studied. The
error of the optimal measurement for n samples is asymptotically compared with
the one of the maximum likelihood estimators from n data given by the optimal
measurement for one sample.Comment: LaTeX, 23 pages, Doctoral Thesi
Universal approximation of multi-copy states and universal quantum lossless data compression
We have proven that there exists a quantum state approximating any multi-copy
state universally when we measure the error by means of the normalized relative
entropy. While the qubit case was proven by Krattenthaler and Slater (IEEE
Trans. IT, 46, 801-819 (2000); quant-ph/9612043), the general case has been
open for more than ten years. For a deeper analysis, we have solved the
mini-max problem concerning `approximation error' up to the second order.
Furthermore, we have applied this result to quantum lossless data compression,
and have constructed a universal quantum lossless data compression
Statistical analysis on testing of an entangled state based on Poisson distribution framework
A hypothesis testing scheme for entanglement has been formulated based on the
Poisson distribution framework instead of the POVM framework. Three designs
were proposed to test the entangled states in this framework. The designs were
evaluated in terms of the asymptotic variance. It has been shown that the
optimal time allocation between the coincidence and anti-coincidence
measurement bases improves the conventional testing method. The test can be
further improved by optimizing the time allocation between the anti-coincidence
bases.Comment: This paper is an extended version of the theoretical part of v1 of
quant-ph/0603254.quant-ph/0603254 is revised so that it is more familiar to
experimentalist
Estimating the spectrum of a density matrix with LOCC
The problem of estimating the spectrum of a density matrix is considered.
Other problems, such as bipartite pure state entanglement, can be reduced to
spectrum estimation. A local operations and classical communication (LOCC)
measurement strategy is shown which is asymptotically optimal. This means that,
for a very large number of copies, it becomes unnecessary to perform collective
measurements which should be more difficult to implement in practice.Comment: 12 pages, uses iopart.cls and iopart10.clo. Improved version. v3:
Reference updated, added journal referenc
Vortex Charging Effect in a Chiral -Wave Superconductor
Quasiparticle states around a single vortex in a -wave
superconductor are studied on the basis of the Bogoliubov-de Gennes (BdG)
theory, where both charge and current screenings are taken into account. Due to
the violation of time reversal symmetry, there are two types of vortices which
are distinguished by their winding orientations relative to the angular
momentum of the chiral Cooper pair. The BdG solution shows that the charges of
the two types of vortices are quite different, reflecting the rotating Cooper
pair of the -wave paring state.Comment: 10 pages, 5 figures, revtex, to be published in Phys. Rev.
Two quantum analogues of Fisher information from a large deviation viewpoint of quantum estimation
We discuss two quantum analogues of Fisher information, symmetric logarithmic
derivative (SLD) Fisher information and Kubo-Mori-Bogoljubov (KMB) Fisher
information from a large deviation viewpoint of quantum estimation and prove
that the former gives the true bound and the latter gives the bound of
consistent superefficient estimators. In another comparison, it is shown that
the difference between them is characterized by the change of the order of
limits.Comment: LaTeX with iopart.cls, iopart12.clo, iopams.st
Additivity and multiplicativity properties of some Gaussian channels for Gaussian inputs
We prove multiplicativity of maximal output norm of classical noise
channels and thermal noise channels of arbitrary modes for all under the
assumption that the input signal states are Gaussian states. As a direct
consequence, we also show the additivity of the minimal output entropy and that
of the energy-constrained Holevo capacity for those Gaussian channels under
Gaussian inputs. To the best of our knowledge, newly discovered majorization
relation on symplectic eigenvalues, which is also of independent interest,
plays a central role in the proof.Comment: 9 pages, no figures. Published Versio
Elementary vortex pinning potential in a chiral p-wave superconductor
The elementary vortex pinning potential is studied in a chiral p-wave
superconductor with a pairing d=z(k_x + i k_y) on the basis of the
quasiclassical theory of superconductivity. An analytical investigation and
numerical results are presented to show that the vortex pinning potential is
dependent on whether the vorticity and chirality are parallel or antiparallel.
Mutual cancellation of the vorticity and chirality around a vortex is
physically crucial to the effect of the pinning center inside the vortex core.Comment: 4 pages, 4 figures include
In-gap state and effect of light illumination in CuIrS probed by photoemission spectroscopy
We have studied disorder-induced in-gap states and effect of light
illumination in the insulating phase of spinel-type CuIrS using
ultra-violet photoemission spectroscopy (UPS). The Ir/Ir
charge-ordered gap appears below the metal-insulator transition temperature.
However, in the insulating phase, in-gap spectral features with are
observed in UPS just below the Fermi level (), corresponding to the
variable range hopping transport observed in resistivity. The spectral weight
at is not increased by light illumination, indicating that the
Ir-Ir dimer is very robust although the long-range octamer order
would be destructed by the photo-excitation. Present results suggest that the
Ir-Ir bipolaronic hopping and disorder effects are responsible
for the conductivity of CuIrS.Comment: 14 pages, 5 figure
Study of a Threshold Cherenkov Counter Based on Silica Aerogels with Low Refractive Indices
To identify and in the region of GeV/c, a
threshold Cherenkov counter equipped with silica aerogels has been
investigated. Silica aerogels with a low refractive index of 1.013 have been
successfully produced using a new technique. By making use of these aerogels as
radiators, we have constructed a Cherenkov counter and have checked its
properties in a test beam. The obtained results have demonstrated that our
aerogel was transparent enough to make up for loss of the Cherenkov photon
yield due to a low refractive index. Various configurations for the photon
collection system and some types of photomultipliers, such as the fine-mesh
type, for a read out were also tested. From these studies, our design of a
Cherenkov counter dedicated to separation up to a few GeV/c %in the
momentum range of GeV/c with an efficiency greater than \%
was considered.Comment: 21 pages, latex format (article), figures included, to be published
in Nucl. Instrm. Meth.
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