2,438 research outputs found
Universal entanglement concentration
We propose a new protocol of \textit{universal} entanglement concentration,
which converts many copies of an \textit{unknown} pure state to an \textit{%
exact} maximally entangled state. The yield of the protocol, which is outputted
as a classical information, is probabilistic, and achives the entropy rate with
high probability, just as non-universal entanglement concentration protocols
do.
Our protocol is optimal among all similar protocols in terms of wide
varieties of measures either up to higher orders or non-asymptotically,
depending on the choice of the measure. The key of the proof of optimality is
the following fact, which is a consequence of the symmetry-based construction
of the protocol: For any invariant measures, optimal protocols are found out in
modifications of the protocol only in its classical output, or the claim on the
product.
We also observe that the classical part of the output of the protocol gives a
natural estimate of the entropy of entanglement, and prove that that estimate
achieves the better asymptotic performance than any other (potentially global)
measurements.Comment: Revised a lot, especially proofs, though no change in theorems,
lemmas itself. Very long, but essential part is from Sec.I to Sec IV-C. Some
of the appendces are almost independent of the main bod
Group theoretical study of LOCC-detection of maximally entangled state using hypothesis testing
In the asymptotic setting, the optimal test for hypotheses testing of the
maximally entangled state is derived under several locality conditions for
measurements. The optimal test is obtained in several cases with the asymptotic
framework as well as the finite-sample framework. In addition, the experimental
scheme for the optimal test is presented
Adaptive experimental design for one-qubit state estimation with finite data based on a statistical update criterion
We consider 1-qubit mixed quantum state estimation by adaptively updating
measurements according to previously obtained outcomes and measurement
settings. Updates are determined by the average-variance-optimality
(A-optimality) criterion, known in the classical theory of experimental design
and applied here to quantum state estimation. In general, A-optimization is a
nonlinear minimization problem; however, we find an analytic solution for
1-qubit state estimation using projective measurements, reducing computational
effort. We compare numerically two adaptive and two nonadaptive schemes for
finite data sets and show that the A-optimality criterion gives more precise
estimates than standard quantum tomography.Comment: 15 pages, 7 figure
Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure
Density-matrix renormalization group is used to study the pairing when both
of electron-electron and electron-phonon interactions are strong in the
Holstein-Hubbard model at half-filling in a region intermediate between the
adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing
correlation obtained for a one-dimensional system is nearly degenerate with the
CDW correlation in a region where the phonon-induced attraction is comparable
with the electron-electron repulsion, but (ii) pairing becomes dominant when we
destroy the electron-hole symmetry in a trestle lattice. This provides an
instance in which pairing can arise, in a lattice-structure dependent manner,
from coexisting electron-electron and electron-phonon interactions.Comment: 4 pages, 3 figures; to appear in Phys. Rev. Let
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
Mineralogy of Y-981971 LL Chondrite and Brecciation Processes of the LL Parent Body
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月30日(金) 国立国語研究所 2階講
Phase estimation via quantum interferometry for noisy detectors
The sensitivity in optical interferometry is strongly affected by losses
during the signal propagation or at the detection stage. The optimal quantum
states of the probing signals in the presence of loss were recently found.
However, in many cases of practical interest, their associated accuracy is
worse than the one obtainable without employing quantum resources (e.g.
entanglement and squeezing) but neglecting the detector's loss. Here we detail
an experiment that can reach the latter even in the presence of imperfect
detectors: it employs a phase-sensitive amplification of the signals after the
phase sensing, before the detection. We experimentally demonstrated the
feasibility of a phase estimation experiment able to reach its optimal working
regime. Since our method uses coherent states as input signals, it is a
practical technique that can be used for high-sensitivity interferometry and,
in contrast to the optimal strategies, does not require one to have an exact
characterization of the loss beforehand.Comment: 4 pages + supplementary information (10 pages), 3 + 4 figure
Uncertainty Relation Revisited from Quantum Estimation Theory
By invoking quantum estimation theory we formulate bounds of errors in
quantum measurement for arbitrary quantum states and observables in a
finite-dimensional Hilbert space. We prove that the measurement errors of two
observables satisfy Heisenberg's uncertainty relation, find the attainable
bound, and provide a strategy to achieve it.Comment: manuscript including 4 pages and 2 figure
Single-component quasicrystalline nanocrystal superlattices through flexible polygon tiling rule
Quasicrystalline superlattices (QC-SLs) generated from single-component colloidal building blocks have been predicted by computer simulations but are challenging to reproduce experimentally. We discovered that 10-fold QC-SLs could self-organize from truncated tetrahedral quantum dots with anisotropic patchiness. Transmission electron microscopy and tomography measurements allow structural reconstruction of the QC-SL from the nanoscale packing to the atomic-scale orientation alignments. The unique QC order leads to a tiling concept, the “flexible polygon tiling rule,” that replicates the experimental observations. The keys for the single-component QC-SL formation were identified to be the anisotropic shape and patchiness of the building blocks and the assembly microscopic environment. Our discovery may spur the creation of various superstructures using anisotropic objects through an enthalpy-driven route
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