Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

The W7-X stellarator is optimized with respect to neoclassical transport.Therefore turbulent transport plays an important role.It is equipped with an inertial cooled graphite divertor which intersects the island chain at the plasma edge depending on the magnetic configuration.Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain.To monitor the effects on the poloidal propagation velocity in the scrape-off layer(SOL)and the plasma edge,an O-mode Poloidal Correlation Reflectometer(PCR)is used which simultaneously monitors the propagation of low-k turbulence.Operating in the density range of 0.6?×?1019 m-3 to2?×?1019 m-3 it covers a large part of the SOL and the plasma edge and allows for the experimental determination in the last closed flux surface(LCFS)and the associated shear layer in low to middensity discharges.In this paper it is shown that the propagation in the shear layer and its vicinity is determined best,when based on an elliptical model.Different magnetic configurations with magnetic edge topology of five independent islands forι?=?1 and six linked islands forι?=?0.81 are investigated.Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied.The coherence spectra of antenna pairs for different poloidal separations is investigated.Using a decomposition method for the measured coherence spectra the characterization of turbulence spectra is possible with respect to e.g.broad band turbulence and quasi coherent modes.A strong reduction of the broad band turbulence is observed in the vicinity of the LCFS which is evidence for the suppression of low-k turbulence at the shear layer.

First principles calculation of spin-related quantities for point defect qubit research

Point defect research in semiconductors has gained remarkable new momentum due to the identification of special point defects that can implement qubits and single photon emitters with unique characteristics.Indeed,these implementations are among the few alternatives for quantum technologies that may operate even at room temperature,and therefore discoveries and characterization of novel point defects may highly facilitate future solid state quantum technologies.First principles calculations play an important role in point defect research,since they provide a direct,extended insight into the formation of the defect states.In the last decades,considerable efforts have been made to calculate spin-dependent properties of point defects from first principles.The developed methods have already demonstrated their essential role in quantitative understanding of the physics and application of point defect qubits.Here,we review and discuss accuracy aspects of these novel ab initio methods and report on their most relevant applications for existing point defect qubits in semiconductors.We pay attention to the advantages and limitations of the methodological solutions and highlight additional developments that are expected in the near future.Moreover,we discuss the opportunity of a systematic search for potential point defect qubits,as well as the possible development of predictive spin dynamic simulations facilitated by ab initio calculations of spin-dependent quantities.

Ex-vivo confocal Raman microspectroscopy of porcine skin with 633/785-NM laser excitation and optical clearing with glycerol/water/DMSO solution

Confocal Raman microspectroscopy(CRM)with 633-and 785-nm excitation wavelengths combined with optical clearing(OC)technique was used for ex-vivo study of porcine skin in the Raman fingerprint region.The optical clearing has been performed on the skin samples by applying a mixture of glycerol and distilled water and a mixture of glycerol,distilled water and chemical penetration enhancer dimethyl sulfoxide(DMSO)during 30 min and 60 min of treat-ment.It was shown that the combined use of the optical clearing technique and CRM at 633 nm allowed one to preserve the high probing depth,signal-to-noise ratio and spectral resolution simultaneously.Comparing the effect of different optical clearing agents on porcine skin showed that an optical clearing agent containing chemical penetration enhancer provides higher optical clearing efficiency.Also,an increase in treatment time allows to improve the optical clearing efficiency of both optical clearing agents.As a result of optical clearing,the detection of the amide-Ⅲ spectral region indicating well-distinguishable structural differences between the type-Ⅰ and type-Ⅳ collagens has been improved.

Characteristic Features of Lapis Lazuli from Different Provenances, Revised by μXRF, ESEM, PGAA and PIXE

The objective of this study is to find out, to what extent the geochemical characteristics of lapis lazuli can be utilized in respect to its provenance. A wide range of variables is taken into consideration depending on the quantity of samples analysed from a specific geological region and the methods applied. In order to provide evidence, a multi-technique analytical approach using μXRF, ESEM, PGAA and PIXE is applied to samples from the most famous deposits of lapis lazuli. Special elements determined as fingerprints are compared in relation to the forming conditions obvious in textural features. The results and statistical output allow a differentiation that enables an optimized local classification of the blue stone. An absolute requirement for all geo-tracing performed on blue colored cultural objects of unknown provenance is awareness of the limits of analysis. The possible sources of lapis lazuli are tested by analysing the blue pigment used as paint on murals and ink on manuscripts from the Silk Road.

Symmetric carbon tetramers forming spin qubits in hexagonal boron nitride

Point defect quantum bits in semiconductors have the potential to revolutionize sensing at atomic scales.Currently,vacancy-related defects are at the forefront of high spatial resolution and low-dimensional sensing.On the other hand,it is expected that impurity-related defect structures may give rise to new features that could further advance quantum sensing in low dimensions.Here,we study the symmetric carbon tetramer clusters in hexagonal boron nitride and propose them as spin qubits for sensing.We utilize periodic-DFT and quantum chemistry approaches to reliably and accurately predict the electronic,optical,and spin properties of the studied defect.We show that the nitrogen-centered symmetric carbon tetramer gives rise to spin state-dependent optical signals with strain-sensitive intersystem crossing rates.Furthermore,the weak hyperfine coupling of the defect to their spin environments results in a reduced electron spin resonance linewidth that can enhance sensitivity.

Phase-field lattice Boltzmann model for dendrites growing and moving in melt flow

The phase-field and lattice Boltzmann methods have been combined to simulate the growth of solid particles moving in melt flow.To handle mobile particles,an overlapping multigrid scheme was developed,in which each individual particle has its own moving grid,with local fields attached to it.Using this approach we were able to simulate simultaneous binary solidification,solute diffusion,melt flow,solid motion,the effect of gravity,and collision of the particles.The method has been applied for describing two possible modes of columnar to equiaxed transition in the Al–Ti system.

A planar defect spin sensor in a two-dimensional material susceptible to strain and electric fields

The boron-vacancy spin defect(V_(B)^(-))in hexagonal boron nitride(hBN)has a great potential as a quantum sensor in a two-dimensional material that can directly probe various external perturbations in atomic-scale proximity to the quantum sensing layer.Here,we apply first-principles calculations to determine the coupling of the VB electronic spin to strain and electric fields.Our work unravels the interplay between local piezoelectric and elastic effects contributing to the final response to the electric fields.The theoretical predictions are then used to analyse optically detected magnetic resonance(ODMR)spectra recorded on hBN crystals containing different densities of V_(B)^(-) centres.We prove that the orthorhombic zero-field splitting parameter results from local electric fields produced by surrounding charge defects.This work paves the way towards applications of V_(B)^(-) centres for quantitative electric field imaging and quantum sensing under pressure.

Ab initio theory of the negatively charged boron vacancy qubit in hexagonal boron nitride

Highly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal.Here,we report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods.By establishing the nature of the bright and dark states as well as the position of the energy levels,we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect.Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids.

Visualization of magnetic fields with cylindrical vector beams in a warm atomic vapor

We propose and demonstrate an experimental implementation for the observation of magnetic fields from spatial features of absorption profiles in a warm atomic vapor.A radially polarized vector beam that traverses atomic vapor will generate an absorption pattern with a petal-like structure by the mediation of a transverse magnetic field(TMF).The spatial absorption pattern rotates when the azimuthal angle of the TMF is changed,while its contrast decreases when the longitudinal component of the magnetic field increases.By analyzing the intensity distribution of the transmitted pattern,we can determine the magnetic field strength.Our work provides a framework for investigating 3 D magnetic field distributions based on atoms.

Growth control of peptide-nanotube spherulitic films： Experiments and simulations

多层次自己组装(MHSA ) 是为许多复杂结构的自发的形成负责的一个关键过程。因为这个过程的复杂性，然而，内在的机制仍然保持大部分不清楚。因此， MHSA 的更深的理解被要求，特别为经由自底向上的方法论的 MHSA 系统的准备。我们这里，试验性地并且理论上出现，肽 nanotube 电影的复杂形成的 MHSA 能完全被操作湿度的试验性的参数控制。而且，我们识别生长前面成核(GFN；在周界的新谷物的形成) 词法进化作为为由有阶段地的相关试验性的观察的观察词法转变的物理背景当模特儿。我们的调查结果显示一个简单方法控制多层次的形态学，为在为实际应用程序构造复杂结构的自底向上的技术的雇用关键。

High harmonic generation and ionization effects in cluster targets

High harmonic generation in gas jets was investigated in different gases up to more than 14 bar backing pressure. The observation of increase of harmonic intensity with increasing pressure and laser intensity shows evidence of the presence of clusters in Xe with an increased efficiency compared with He, whereas Ar is an intermediate case for which clusters will start to dominate above a certain backing pressure. Spectral investigations give evidence for tunable harmonic generation in a broad spectral range. A spectral shift of opposite signature caused by the free electrons in the focal volume and the nanoplasmas inside the cluster was observed.

An L-band emitter with quantum memory in silicon

Fluorescent centres in silicon have recently attracted great interest,owing to their remarkable properties for quantum technology.Here,we demonstrate that the C-centre in silicon can realise an optically readable quantum register in the L-band wavelength region where the transmission losses in commercial optical fibres are minimal.Our in-depth theoretical characterisation confirms the assignment of the C-centre to the carbon-oxygen interstitial pair defect.We further explore its magneto-optical properties,such as hyperfine and spin-orbit coupling constants from first principles calculations,which are crucial for tight control of the quantum states of the triplet electron spin.Based on this data,we set up quantum optics protocols to initialise and read out the quantum states of the electron spin,and realise a quantum memory by transferring quantum information from the electron spin to proximate ^(29)Si nuclear spins.Our findings establish an optically readable long-living quantum memory in silicon where the scalability of qubits may be achieved by CMOS-compatible technology.

The (e_(g)■e_(u))■E_(g) product Jahn-Teller effect in the neutral group-Ⅳ vacancy quantum bits in diamond

The product Jahn-Teller effect may occur for such coupled electron-phonon systems in solids where single electrons occupy double degenerate orbitals.We propose that the excited state of the neutral XV split-vacancy complex in diamond,where X and V labels a group-Ⅳ impurity atom of X=Si,Ge,Sn,Pb and the vacancy,respectively,is such a system with e_(g) and e_(u) double degenerate orbitals and E_(g) quasi-localized phonons.We develop and apply ab initio theory to quantify the strength of electron–phonon coupling for neutral XV complexes in diamond,and find a significant impact on the corresponding optical properties of these centers.Our results show good agreement with recent experimental data on the prospective SiV(0)quantum bit,and reveals the complex nature of the excited states of neutral XV color centers in diamond.

Dipolar spin relaxation of divacancy qubits in silicon carbide

Divacancy spins implement qubits with outstanding characteristics and capabilities in an industrial semiconductor host On the other hand,there are still numerous open questions about the physics of these important defects,for instance,spin relaxation has not been thoroughly studied yet.Here,we carry out a theoretical study on environmental spin-induced spin relaxation processes of divacancy qubits in the 4H polytype of silicon carbide(4H-SiC).We reveal all the relevant magnetic field values where the longitudinal spin relaxation time T,drops resonantly due to the coupling to either nuclear spins or electron spins.We quantitatively analyze the dependence of the T,time on the concentration of point defect spins and the applied magnetic field and provide ananalytical expression.We demonstrate that dipolar spin relaxation plays a significant role both in as-grown and ion-implanted samples and it often limits the coherence time of divacancy qubits in 4H-SiC.

Stone–Wales defects in hexagonal boron nitride as ultraviolet emitters

Many quantum emitters have been measured close or near the grain boundaries of the two-dimensional hexagonal boron nitride where various Stone–Wales defects appear.We show by means of first principles density functional theory calculations that the pentagon–heptagon Stone–Wales defect is an ultraviolet emitter and its optical properties closely follow the characteristics of a 4.08-eV quantum emitter,often observed in polycrystalline hexagonal boron nitride.We also show that the square–octagon Stone–Wales line defects are optically active in the ultraviolet region with varying gaps depending on their density in hexagonal boron nitride.Our results may introduce a paradigm shift in the identification of fluorescent centres in this material.