1,783 research outputs found
Ordered Measurements of Permutationally-Symmetric Qubit Strings
We show that any sequence of measurements on a permutationally-symmetric
(pure or mixed) multi-qubit string leaves the unmeasured qubit substring also
permutationally-symmetric. In addition, we show that the measurement
probabilities for an arbitrary sequence of single-qubit measurements are
independent of how many unmeasured qubits have been lost prior to the
measurement. Our results are valuable for quantum information processing of
indistinguishable particles by post-selection, e.g. in cases where the results
of an experiment are discarded conditioned upon the occurrence of a given event
such as particle loss. Furthermore, our results are important for the design of
adaptive-measurement strategies, e.g. a series of measurements where for each
measurement instance, the measurement basis is chosen depending on prior
measurement results.Comment: 13 page
Unidirectional light emission from high-Q modes in optical microcavities
We introduce a new scheme to design optical microcavities supporting high-Q
modes with unidirectional light emission. This is achieved by coupling a low-Q
mode with unidirectional emission to a high-Q mode. The coupling is due to
enhanced dynamical tunneling near an avoided resonance crossing. Numerical
results for a microdisk with a suitably positioned air hole demonstrate the
feasibility and the potential of this concept.Comment: 4 pages, 6 figures (in reduced resolution
Diffusion Limited Aggregation with Power-Law Pinning
Using stochastic conformal mapping techniques we study the patterns emerging
from Laplacian growth with a power-law decaying threshold for growth
(where is the radius of the particle cluster). For
the growth pattern is in the same universality class as diffusion
limited aggregation (DLA) growth, while for the resulting patterns
have a lower fractal dimension than a DLA cluster due to the
enhancement of growth at the hot tips of the developing pattern. Our results
indicate that a pinning transition occurs at , significantly
smaller than might be expected from the lower bound
of multifractal spectrum of DLA. This limiting case shows that the most
singular tips in the pruned cluster now correspond to those expected for a
purely one-dimensional line. Using multifractal analysis, analytic expressions
are established for both close to the breakdown of DLA universality
class, i.e., , and close to the pinning transition, i.e.,
.Comment: 5 pages, e figures, submitted to Phys. Rev.
Fermi-Edge Singularities in the Mesoscopic X-Ray Edge Problem
We study the x-ray edge problem for a chaotic quantum dot or nanoparticle
displaying mesoscopic fluctuations. In the bulk, x-ray physics is known to
produce deviations from the naively expected photoabsorption cross section in
the form of a peaked or rounded edge. For a coherent system with chaotic
dynamics, we find substantial changes and in particular that a photoabsorption
cross section showing a rounded edge in the bulk will change to a slightly
peaked edge on average as the system size is reduced to a mesoscopic (coherent)
scale.Comment: 4 pages, 3 figures, final version as published in PR
Saccharopolyspora cebuensis sp. nov., a novel actinomycete isolated from a Philippine sponge (Porifera)
The taxonomic status of a marine actinomycete isolated from the sponge Haliclona sp. collected from Cebu, Philippines, was established using both phenotypic and genotypic data. Strain SPE 10-1(T) exhibited chemotaxonomic and morphological characteristics that were consistent with those of members of the genus Saccharopolyspora. It showed a strict requirement for salt and is the first obligate marine bacterium of the genus Saccharopolyspora to be isolated. The principal isoprenoid quinone detected was MK-9(H(4)). The fatty acid pattern consisted mainly of terminally branched iso and anteiso fatty acids. The DNA G+C content was 72.6 mol%. Analysis of the 16S rRNA gene sequence supported affiliation of the strain with the genus Saccharopolyspora; the type strain of Saccharopolyspora gregorii was the closest phylogenetic relative (96 % sequence similarity). Sequence similarities of strain SPE 10-1(T) to other type strains of this genus were 93-95 %. It is proposed that strain SPE 10-1(T) should be classified in the genus Saccharopolyspora as a representative of Saccharopolyspora cebuensis sp. nov. The type strain of Saccharopolyspora cebuensis is SPE 10-1(T) (=DSM 45019(T)=CIP 109355(T))
Fermi Edge Singularities in the Mesoscopic Regime: I. Anderson Orthogonality Catastrophe
For generic mesoscopic systems like quantum dots or nanoparticles, we study
the Anderson orthogonality catastrophe (AOC) and Fermi edge singularities in
photoabsorption spectra in a series of two papers. In the present paper we
focus on AOC for a finite number of particles in discrete energy levels where,
in contrast to the bulk situation, AOC is not complete. Moreover, fluctuations
characteristic for mesoscopic systems lead to a broad distribution of AOC
ground state overlaps. The fluctuations originate dominantly in the levels
around the Fermi energy, and we derive an analytic expression for the
probability distribution of AOC overlaps in the limit of strong perturbations.
We address the formation of a bound state and its importance for symmetries
between the overlap distributions for attractive and repulsive potentials. Our
results are based on a random matrix model for the chaotic conduction electrons
that are subject to a rank one perturbation corresponding, e.g., to the
localized core hole generated in the photoabsorption process.Comment: 10 pages, 8 figures, submitted to Phys. Rev.
Absorption of Ultrashort Laser Pulses in Strongly Overdense Targets
We report on the first absorption experiments of sub-10 fs high-contrast
Ti:Sa laser pulses incident on solid targets. The very good contrast of the
laser pulse assures the formation of a very small pre-plasma and the pulse
interacts with the matter close to solid density. Experimental results indicate
that p-polarized laser pulses are absorbed up to 80 percent at 80 degrees
incidence angle. The simulation results of PSC PIC code clearly confirm the
observations and show that the collisionless absorption works efficiently in
steep density profiles
Temperature-dependent proximity magnetism in Pt
We experimentally demonstrate the existence of magnetic coupling between two
ferromagnets separated by a thin Pt layer. The coupling remains ferromagnetic
regardless of the Pt thickness, and exhibits a significant dependence on
temperature. Therefore, it cannot be explained by the established mechanisms of
magnetic coupling across nonmagnetic spacers. We show that the experimental
results are consistent with the presence of magnetism induced in Pt in
proximity to ferromagnets, in direct analogy to the well-known proximity
effects in superconductivity.Comment: 4 pages, 3 figure
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