6,567 research outputs found
Efficient out-coupling of high-purity single photons from a coherent quantum dot in a photonic-crystal cavity
We demonstrate a single-photon collection efficiency of from
a quantum dot in a low-Q mode of a photonic-crystal cavity with a single-photon
purity of recorded above the saturation power. The high
efficiency is directly confirmed by detecting up to kilocounts per
second on a single-photon detector on another quantum dot coupled to the cavity
mode. The high collection efficiency is found to be broadband, as is explained
by detailed numerical simulations. Cavity-enhanced efficient excitation of
quantum dots is obtained through phonon-mediated excitation and under these
conditions, single-photon indistinguishability measurements reveal long
coherence times reaching ns in a weak-excitation regime. Our work
demonstrates that photonic crystals provide a very promising platform for
highly integrated generation of coherent single photons including the efficient
out-coupling of the photons from the photonic chip.Comment: 13 pages, 8 figures, submitte
Ellipsometric measurements of the refractive indices of linear alkylbenzene and EJ-301 scintillators from 210 to 1000 nm
We report on ellipsometric measurements of the refractive indices of LAB-PPO,
Nd-doped LAB-PPO and EJ-301 scintillators to the nearest +/-0.005, in the
wavelength range 210-1000 nm.Comment: 7 pages, 4 figure
Simple Ginzburg-Landau Theory for Vortices in a Crystal Lattice
We study the Ginzburg-Landau model with a nonlocal quartic term as a simple
phenomenological model for superconductors in the presence of coupling between
the vortex lattice and the underlying crystal lattice. In mean-field theory,
our model is consistent with a general oblique vortex lattice ranging from a
triangular lattice to a square lattice. This simple formulation enables us to
study the effect of thermal fluctuations in the vortex liquid regime. We
calculate the structure factor of the vortex liquid nonperturbatively and find
Bragg-like peaks with four-fold symmetry appearing in the structure factor even
though there is only a short-range crystalline order.Comment: Revised version with new title and additional results for the vortex
liquid regime, to be published in Phys. Rev. Lett. 5 pages RevTeX, 1 figure
include
Detection of Gravitational Wave - An Application of Relativistic Quantum Information Theory
We show that a passing gravitational wave may influence the spin entropy and
spin negativity of a system of massive spin-1/2 particles, in a way that is
characteristic of the radiation. We establish the specific conditions under
which this effect may be nonzero. The change in spin entropy and negativity,
however, is extremely small. Here, we propose and show that this effect may be
amplified through entanglement swapping. Relativistic quantum information
theory may have a contribution towards the detection of gravitational wave.Comment: 9 page
A Patterned Architecture of Monoaminergic Afferents in the Cerebellar Cortex: Noradrenergic and Serotonergic Fibre Distributions within Lobules and Parasagittal Zones
The geometry of the glutamatergic mossy-parallel fibre and climbing fibre inputs to cerebellar cortical Purkinje cells has powerfully influenced thinking about cerebellar functions. The compartmentation of the cerebellum into parasagittal zones, identifiable in olivo-cortico-nuclear projections, and the trajectories of the parallel fibres, transverse to these zones and following the long axes of the cortical folia, are particularly important. Two monoaminergic afferent systems, the serotonergic and noradrenergic, are major inputs to the cerebellar cortex but their architecture and relationship with the cortical geometry are poorly understood. Immunohistochemistry for the serotonin transporter (SERT) and for the noradrenaline transporter (NET) revealed strong anisotropy of these afferent fibres in the molecular layer of rat cerebellar cortex. Individual serotonergic fibres travel predominantly medial-lateral, along the long axes of the cortical folia, similar to parallel fibres and Zebrin II immunohistochemistry revealed that they can influence multiple zones. In contrast, individual noradrenergic fibres run predominantly parasagittally with rostral-caudal extents significantly longer than their medial-lateral deviations. Their local area of influence has similarities in form and size to those of identified microzones. Within the molecular layer, the orthogonal trajectories of these two afferent systems suggest different information processing. An individual serotonergic fibre must influence all zones and microzones within its medial-lateral trajectory. In contrast, noradrenergic fibres can influence smaller cortical territories, potentially as limited as a microzone. Evidence is emerging that these monoaminergic systems may not supply a global signal to all of their targets and their potential for cerebellar cortical functions is discussed
Automatic Identification of Crystal Structures and Interfaces via Artificial-Intelligence-based Electron Microscopy
Characterizing crystal structures and interfaces down to the atomic level is
an important step for designing advanced materials. Modern electron microscopy
routinely achieves atomic resolution and is capable to resolve complex
arrangements of atoms with picometer precision. Here, we present AI-STEM, an
automatic, artificial-intelligence based method, for accurately identifying key
characteristics from atomic-resolution scanning transmission electron
microscopy (STEM) images of polycrystalline materials. The method is based on a
Bayesian convolutional neural network (BNN) that is trained only on simulated
images. AI-STEM automatically and accurately identifies crystal structure,
lattice orientation, and location of interface regions in synthetic and
experimental images. The model is trained on cubic and hexagonal crystal
structures, yielding classifications and uncertainty estimates, while no
explicit information on structural patterns at the interfaces is included
during training. This work combines principles from probabilistic modeling,
deep learning, and information theory, enabling automatic analysis of
experimental, atomic-resolution images.Comment: Code (https://github.com/AndreasLeitherer/ai4stem) and data
(https://doi.org/10.5281/zenodo.7756516) are available for public use. The
manuscript contains 32 pages (10 pages main text, 15 pages for Methods &
References & 5 Figures & 1 Table, as well as 7 pages Supplementary
Information), including 5 main figures and 6 supplementary figure
Teleportation via thermally entangled state of a two-qubit Heisenberg XX chain
We find that quantum teleportation, using the thermally entangled state of
two-qubit Heisenberg XX chain as a resource, with fidelity better than any
classical communication protocol is possible. However, a thermal state with a
greater amount of thermal entanglement does not necessarily yield better
fidelity. It depends on the amount of mixing between the separable state and
maximally entangled state in the spectra of the two-qubit Heisenberg XX model.Comment: 5 pages, 1 tabl
Memory consolidation in the cerebellar cortex
Several forms of learning, including classical conditioning of the eyeblink, depend upon the cerebellum. In examining mechanisms of eyeblink conditioning in rabbits, reversible inactivations of the control circuitry have begun to dissociate aspects of cerebellar cortical and nuclear function in memory consolidation. It was previously shown that post-training cerebellar cortical, but not nuclear, inactivations with the GABA(A) agonist muscimol prevented consolidation but these findings left open the question as to how final memory storage was partitioned across cortical and nuclear levels. Memory consolidation might be essentially cortical and directly disturbed by actions of the muscimol, or it might be nuclear, and sensitive to the raised excitability of the nuclear neurons following the loss of cortical inhibition. To resolve this question, we simultaneously inactivated cerebellar cortical lobule HVI and the anterior interpositus nucleus of rabbits during the post-training period, so protecting the nuclei from disinhibitory effects of cortical inactivation. Consolidation was impaired by these simultaneous inactivations. Because direct application of muscimol to the nuclei alone has no impact upon consolidation, we can conclude that post-training, consolidation processes and memory storage for eyeblink conditioning have critical cerebellar cortical components. The findings are consistent with a recent model that suggests the distribution of learning-related plasticity across cortical and nuclear levels is task-dependent. There can be transfer to nuclear or brainstem levels for control of high-frequency responses but learning with lower frequency response components, such as in eyeblink conditioning, remains mainly dependent upon cortical memory storage
Liquid-to-liquid phase transition in pancake vortex systems
We study the thermodynamics of a model of pancake vortices in layered
superconductors. The model is based on the effective pair potential for the
pancake vortices derived from the London approximation of a version of the
Lawrence-Doniach model which is valid for extreme type-II superconductors.
Using the hypernetted-chain (HNC) approximation, we find that there is a
temperature below which multiple solutions to the HNC equations exist. By
explicitly evaluating the free energy for each solution we find that the system
undergoes a first-order transition between two vortex liquid phases. The
low-temperature phase has larger correlations along the field direction than
the high-temperature phase. We discuss the possible relation of this phase
transition to the liquid-to-liquid phase transition recently observed in
Y-Ba-Cu-O superconductors in high magnetic fields in the presence of disorder.Comment: 7 pages, 6 figure
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