A Holevo-Type Bound for a Hilbert Schmidt Distance Measure

We prove a new version of the Holevo bound employing the Hilbert-Schmidt norm instead of the Kullback-Leibler divergence. Suppose Alice is sending classical information to Bob by using a quantum channel while Bob is performing some projective measurements. We bound the classical mutual information in terms of the Hilbert-Schmidt norm by its quantum Hilbert-Schmidt counterpart. This constitutes a Holevo-type upper bound on the classical information transmission rate via a quantum channel. The resulting inequality is rather natural and intuitive relating classical and quantum expressions using the same measure.

Revealing the Defect-Dominated Electron Scattering in Mg_(3)Sb_(2)-Based Thermoelectric Materials

The thermoelectric parameters are essentially governed by electron and phonon transport.Since the carrier scattering mechanism plays a decisive role in electron transport,it is of great significance for the electrical properties of thermoelectric materials.As a typical example,the defect-dominated carrier scattering mechanism can significantly impact the room-temperature electron mobility of n-type Mg_(3)Sb_(2)-based materials.However,the origin of such a defect scattering mechanism is still controversial.Herein,the existence of the Mg vacancies and Mg interstitials has been identified by synchrotron powder X-ray diffraction.The relationship among the point defects,chemical compositions,and synthesis conditions in Mg_(3)Sb_(2)-based materials has been revealed.By further introducing the point defects without affecting the grain size via neutron irradiation,the thermally activated electrical conductivity can be reproduced.Our results demonstrate that the point defects scattering of electrons is important in the n-type Mg_(3)Sb_(2)-based materials.

Search for the doubly heavy baryon Ξ_(bc)^(+)→ decaying to J/ψΞ_(c)^(+)

A first search for the Ξ_(bc)^(+)J/ψΞ_(c)^(+) decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1 recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local (global) significance of 4.3(2.8) and 4.1(2.4) standard deviations at masses of 6571 and 6694 MeV/c2, respectively. Upper limits are set on the Ξ+bc baryon production cross-section times the branching fraction relative to that of the B+c→J/ψD+s decay at centre-of-mass energies of 8 and 13 TeV, in the Ξ+bc and in the B+c rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to 20GeV/c, respectively. Upper limits are presented as a function of the Ξ+bc mass and lifetime.

Search for the rare decays W^(+)→D_(s)^(+)γ and Z→D^(0)γ at LHCb

A search for the rare decays W^(+)→D_(s)^(+)γ and Z→D0γis performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV,corresponding to an integrated luminosity of 2.0fb−1.No significant signal is observed for either decay mode and upper limits on their branching fractions are set using W^(+)→D_(s)^(+)γ and Z→μ+μ−decays as normalization channels.The upper limits are 6.5×10^(−4) and 2.1×10^(−3) at 95% confidence level for the W^(+)→D_(s)^(+)γ and Z→D^(0)γ decay modes,respectively.This is the first reported search for the Z→D^(0)γ decay,while the upper limit on the W+→D+sγbranching fraction improves upon the previous best limit.

In Situ Etching for Total Control Over Axial and Radial Nanowire Growth

We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway,independent of other growth parameters.Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth.We demonstrate the method using etching by HCl during InP nanowire growth.The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching.

IN-SITU AFM OF POLYMER CRYSTALLIZATION

Atomic force microscopy images taken during the crystallization of polyethylene both from processed andquiescent melts are presented. Crystallization from processed melts provides further evidence of a region in front of agrowing lamella that is influenced by the crystallization process, but extending only 40 nm into the melt. High-resolutionimages of the growing crystal tip, taken during crystallization, show no direct evidence of the existence of intermediatephases. The growing tip is shown to be slightly rounded. In-filling crystallization, occurring after the initial flush of growth,is imaged in polyethylene for the first time, and shown to continue to a temperature 8℃ below the initial crystallizationtemperature.

Study of the production of Λ_b^0 band ~0 hadrons in pp collisions and first measurement of the Λ_b^0→J/ψpK^- branching fraction

The product of the ∧0/b （-B/0） differential production cross-section and the branching fraction of the decay ∧0/b→ J/ψ pK-（-B/0→ J/ψ-K＊（892）0）is measured as a function of the beauty hadron transverse momentum, PT, and rapidity, y. The kinematic region of the measurements is pT〈20 GeV/c and 2.0 〈g〈4.5.The measurements use a data sample corresponding to an integrated luminosity of 3fb-1 collected by the LHCb detector in pp collisions at centre-of-mass energies √s=7 TeV in 2011 and √s=8 TeV in 2012. Based on previous LHCb results of the fragmentation fraction ratio,f∧0/b/fd,the branching fraction of the decay ∧0/b→ J/ψ pK-is measured to be B（∧0/b→ J/ψ pK-）=（3.17±0.04±0.07±0.34＋0.45/-0.28）×10-4,where the first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay -B/0 →J/ψ-K＊（892）0,and the fourth is due to the knowledge of f∧0/b/fd.The sum of the asymmetries in the production and decay between ∧0/b and ∧0/bis also measured as a function of PT and y.The previously published branching fraction of ∧0/b→ J/ψ pπ-,relative to that of ∧0/b→ J/ψ pK-,is updated. The branching fractions of ∧0/b→P＋c（→ J/ψp）K-are determined.

Finding tree symmetries using continuous-time quantum walk

Quantum walk, the quantum counterpart of random walk, is an important model and widely studied to develop new quantum algorithms. This paper studies the relationship between the continuous-time quantum walk and the symmetry of a graph, especially that of a tree. Firstly, we prove in mathematics that the symmetry of a graph is highly related to quantum walk. Secondly, we propose an algorithm based on the continuous-time quantum walk to compute the symmetry of a tree. Our algorithm has better time complexity O（N3） than the current best algorithm. Finally, through testing three types of 10024 trees, we find that the symmetry of a tree can be found with an extremely high efficiency with the help of the continuous-time quantum walk.

Route-asymmetrical light transmission of a fiber-chip-fiber optomechanical system

In this paper, we proposed and experimentally demonstrated a route-asymmetrical light transmission scheme based on the thermal radiative effect, which means that forward and backward propagations of an optical device have different transmittances provided they are not present simultaneously. Employing a fiber-chipfiber optomechanical system, our scheme has successfully achieved a broad operation bandwidth of at least 24 nm and an ultra-high route-asymmetrical transmission ratio （RATR） up to 63 dB. The route-asymmetrical device has been demonstrated effectively with not only the continuous-wave （CW） light but also 10 Gbit/s on-off-keying （OOK） digital signals. Above mentioned unique features can be mostly attributed to the significant characteristics of the thermal radiative effect, which could cause a fiber displacement up to tens of microns. The powerful and significant thermal radiative effect opens up a new opportunity and method for route-asymmetrical light transmission. Moreover, this research may have important applications in all-optical systems, such as the optical limiters and ultra-low loss switches.

Search for the doubly heavy baryons Ω^(0)_(bc) and E^(0)_(bc) decaying to Λ^(+)_(c)π^(-) and E^(+)_(c)π^(-)

The first search for the doubly heavyΩ^(0)_(bc)baryon and a search for the E^(0)_(bc)baryon are performed using pp collision data collected via the LHCb experiment from 2016 to 2018 at a centre-of-mass energy of 13 TeV,corresponding to an integrated luminosity of 5.2 fb^(-1).The baryons are reconstructed via their decays to Λ^(+)_(c)π^(-)and E^(+)_(c)π^(-).No significant excess is fbund for invariant masses between 6700 and 7300 MeV/c^(2),in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20 MeV/c.Upper limits are set on the ratio of the Ω^(0)_(bc)and E^(0)_(bc)production cross-section times the branching fraction to Λ^(+)_(c)π^(-)(E^(+)_(c)π^(-))relative to that of the Λ^(0)_(b)(E^(0)_(b))baryon,for different lifetime hypotheses,at 95%confidence level.The upper limits range from 0.5 x 10^(-4)to 2.5 x 10^(-4)for theΩ^(0)_(bc)→Λ^(+)_(c)π^(-)(E^(0)_(bc)→Λ^(+)_(c)π^(-))decay,and from 1.4x 10^(-3)to 6.9 x 10^(-3)for theΩ^(0)_(bc)→E^(+)_(c)π^(-)(E^(0)_(bc)→E^(+)_(c)π^(-))decay,depending on the considered mass and lifetime of theΩ^(0)_(bc)(E^(0)_(bc))baryon.

Search for the rare decay B^(0)→J/ψФ

A search for the rare decay B^(0)→J/ψФis performed using Pp collision data collected with the LHCb dete-ctor at centre-of-mass energies of 7,8 and 13 TeV,corresponding to an integrated luminosity of9 fb.No significant signal of the decay is observed and an upper limitof 1.1x 10^(-7)at 90%confidence level is set on the branching fraction.

探究高温超导物理规律的新范式

A key goal of superconductivity research is to identify the mechanism by which electrons pair.Clues to the pairing mechanism lie in the resistive behavior(that is itself governed by electrons scattering off impurities and dynamical fluctuations within the material)above the superconducting transition temperature T_(c).

Measurement of Ξcc++ production in pp collisions at s1/2=13 TeV

The production of ■baryons in proton-proton collisions at a centre-of-mass energy of √s = 13 TeV is measured in the transverse-momentum range 4<pT<15GeV/c and the rapidity range2.0<y<4.5.The data used in this measurement correspond to an integrated luminosity of 1.7fb^-1,recorded by the LHCb experiment during 2016.The ratio of the ■ production cross-section times the branching fraction of the■→∧^+cK^-π^+ π^+decay relative to the prompt ∧^+c production cross-section is found to be(2.22±0.27±0.29)×10^-4,assuming the central value of the measured lifetime,where the first uncertainty is statistical and the second systematic.

■^(−)_(b)→J/ψΛK^(−)衰变中一个J/ψΛ结构的迹象与■^(−)激发态的发现

夸克和胶子组成的粒子统称强子,其中包含4个或以上组分夸克的强子被称为奇异强子.目前实验上发现的奇异强子最多包含5个夸克,称为五夸克态.对五夸克态的深入研究可以检验对强相互作用的理解.利用质心能量为7、8和13 TeV,总积分亮度9 fb^(−1)的质子-质子对撞数据,大型强子对撞机底夸克实验(LHCb)采用全谱分析的方法,研究了■^(−)_(b)→J/ψΛK^(−)衰变过程中的共振态结构.实验发现J/ψΛ系统中存在质量约为4.46 MeV/c^(2)的共振结构存在的迹象,其显著程度为3.1倍标准偏差,性质与五夸克态相符.这是实验上首次观测到包含奇异夸克的五夸克态的存在证据,为五夸克态的理论研究和后续的实验探索提供了重要的依据.除此之外,实验还精细测量了ΛK−系统中部分共振态的共振参数,精度远高于当前世界平均值,这对加深传统重子谱学的认识有着重要的意义.