Quantum Fisher information of a qubit-qutrit system in Garfinkle–Horowitz–Strominger dilation space–time

We investigate the quantum Fisher information(QFI) of a qubit-qutrit system in the background of Garfinkle–Horowitz–Strominger dilation black hole. After deriving the analytical expression of the QFI, we examine its dynamics with respect to the dilation parameter D and the state parameter γ of the system. Our results show that the QFI for the estimation of γ is a fixed value,which is independent of the parameters D and γ. And the QFI for the estimation of D varies with the parameters D and γ. Additionally, we propose an effective strategy to steer the QFI by introducing weak measurement reversal. We find that the QFI can be remarkably enhanced by adjusting the appropriate reversing measurement strengths. Our findings might provide some useful insights for the study on parameter estimation of hybrid systems in the framework of relativity theory.     

Quantum thermal field fluctuation induced corrections to the interaction between two ground-state atoms

We generalize the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji (the DDC formalism) in the fourth order for two atoms in interaction with scalar fields in vacuum to a thermal bath at finite temperature T, and then calculate the interatomic interaction energy of two ground-state atoms separately in terms of the contributions of thermal fluctuations and the radiation reaction of the atoms and analyze in detail the thermal corrections to the van der Waals and Casimir–Polder interactions. We discover a particular region, i.e. $\sqrt[4]{{\lambda }^{3}\beta }\ll L\ll \lambda $ with L, β and λ denoting the interatomic separation, the wavelength of thermal photons and the transition wavelength of the atoms respectively, where the thermal corrections remarkably render the van der Waals force, which is usually attractive, repulsive, leading to an interesting crossover phenomenon of the interatomic interaction from attractive to repulsive as the temperature increases. We also find that the thermal corrections cause significant changes to the Casimir–Polder force when the temperature is sufficiently high, resulting in an attractive force proportional to TL⁻³ in the λ ≪ β ≪ L region, and a force that can be either attractive or repulsive and even vanishing in the β ≪ λ ≪ L region depending on the interatomic separation.     

Spatial-dependent probe transmission based high-precision two-dimensional atomic localization

Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology.     

Geminga contribution to the cosmic-ray positron excess according to the gamma-ray observations

We attempt to interpret the cosmic-ray positron excess by injection from the nearby pulsar Geminga, assuming a two-zone diffusion scenario and an injection spectrum with a low energy cutoff. Since the high energy positrons and electrons from Geminga can induce γ rays via inverse Compton scattering, we take into account the extended γ-ray observations around Geminga from HAWC for ∼10 TeV and from Fermi-LAT for ${ \mathcal O }(10)$ GeV. According to the extended γ-ray observation claimed by an analysis of Fermi-LAT data, we find that Geminga could explain the positron excess for a 30% energy conversion efficiency into positrons and electrons. However, based on the constraint on the extended γ rays given by another Fermi-LAT analysis, positrons from Geminga would be insufficient to account for the positron excess. Further robust analysis of Fermi-LAT data for the extended γ rays would be crucial to determine whether Geminga can explain the positron excess or not.     

Singularities and accumulation of singularities of πN scattering amplitudes

It is demonstrated that for the isospin I = 1/2 πN scattering amplitude, T^I=1/2(s, t), $s={\left({m}_{N}^{2}-{m}_{\pi }^{2}\right)}^{2}/{m}_{N}^{2}$ and $s={m}_{N}^{2}+2{m}_{\pi }^{2}$ are two accumulation points of poles on the second sheet of complex s plane, and are hence accumulation of singularities of T^I=1/2(s, t). For T^I=3/2(s, t), $s={\left({m}_{N}^{2}-{m}_{\pi }^{2}\right)}^{2}/{m}_{N}^{2}$ is the accumulation point of poles on the second sheet of the complex s plane. The proof is valid up to all orders of chiral expansions.     

Preferential attachment network model with aging and initial attractiveness

In this paper, we generalize the growing network model with preferential attachment for new links to simultaneously include aging and initial attractiveness of nodes. The network evolves with the addition of a new node per unit time, and each new node has m new links that with probability Π_i are connected to nodes i already present in the network. In our model, the preferential attachment probability Π_i is proportional not only to k_i + A, the sum of the old node i's degree k_i and its initial attractiveness A, but also to the aging factor ${\tau }_{i}^{-\alpha }$, where τ_i is the age of the old node i. That is, ${{\rm{\Pi }}}_{i}\propto ({k}_{i}+A){\tau }_{i}^{-\alpha }$. Based on the continuum approximation, we present a mean-field analysis that predicts the degree dynamics of the network structure. We show that depending on the aging parameter α two different network topologies can emerge. For α < 1, the network exhibits scaling behavior with a power-law degree distribution P(k) ∝ k^−γ for large k where the scaling exponent γ increases with the aging parameter α and is linearly correlated with the ratio A/m. Moreover, the average degree k(t_i, t) at time t for any node i that is added into the network at time t_i scales as $k({t}_{i},t)\propto {t}_{i}^{-\beta }$ where 1/β is a linear function of A/m. For α > 1, such scaling behavior disappears and the degree distribution is exponential.     

在线社交网络中群体互动行为的时间特征

针对在线社交网络中群体互动行为,运用有偏扩散理论,构建有偏扩散模型,从任务的间隔时间τ与执行时间θ的关系视角,系统地阐述了群体互动活动中群体发帖行为与事件行为的时间间隔分布特征.针对群体用户发帖时τ≥θ的特征,论证群体用户发帖时间间隔的幂律分布机理.针对事件时τ>>θ的特征,论证了事件时间间隔具有指数效应的幂律分布机理,实验结果与理论推导吻合.     

Energy conditions of the f(T,B) gravity dark energy model with the validity of thermodynamics

In this article, the analysis of Tsallis holographic dark energy(which turns into holographic dark energy for a particular choice of positive non-additivity parameter δ) in modified f(T, B) gravity with the validity of thermodynamics and energy conditions for a homogeneous and isotropic FLRW Universe has been studied. The enlightenment of the field equation towards f(T,B)=αT~m+βB~n, made possible by the fact that the model is purely accelerating,corresponds to q=-0.54(Mamon and Das 2017 Eur. Phys.J.C 77 49). The generalized second law of thermodynamics is valid not only for the same temperature inside the horizon, but also for the apparent horizon for a change in temperature. The essential inspiration driving this article is to exhibit the applicability that the holographic dark energy achieved from standard Tsallis holographic dark energy and the components acquired from f(T, B) gravity are identical for the specific bounty of constants. The analysis of energy conditions confirms that the weak energy condition and the null energy condition are fulfilled throughout the expansion, while violation of the strong energy condition validates the accelerated expansion of the Universe.With the expansion, the model becomes a quintessence dominated model. The dominant energy condition is not observed initially when the model is filled with genuine baryonic matter,whereas it appears when the model is in the quintessence dominated era.     

Two-proton radioactivity of exotic nuclei beyond proton drip-line

To search for new candidates of the true and simultaneous two-proton(2 p) radioactivity, the 2 p decay energies(Q2 p) are extracted by the Weizs?cker–Skyrme-4(WS4) model, the finite-range droplet model(FRDM), the Koura–Tachibana–Uno–Yamada(KTUY) model and the Hartree–Fock–Bogoliubov mean-field model with the BSk29 Skyrme interaction(HFB29). Then, the 2 p radioactivity half-lives are calculated within the generalized liquid drop model by inputting the four types of Q2 pvalues. By the energy and half-life constraints, it is found that the probable 2 p decay candidates are the nuclei beyond the proton-drip line in the region of Z≤50 based on the WS4 and KTUY mass models. For the FRDM mass model, the probable 2 p decay candidates are found in the region of Z≤44. However, the 2p-decaying candidates are predicted in the region of Z≤58 by the HFB29 mass model. It means that the probable 2 p decay candidates of Z50 are only predicted by the HFB29 mass model. Finally, the competition between the true 2p radioactivity and α-decay for the nuclei above the N=Z=50 shell closures is discussed. It is shown that ~(101)Te,~(111)Ba and ~(114)Ce prefer to 2p radioactivity and the dominant decay mode of ~(107)Xe and ~(116)Ce is α-decay.     

Shadows and observational appearance of a new family of Ayón-Beato-García black holes

In this paper, we study the shadows and observational appearance of the Ayón-Beato-García (ABG) black hole, which is surrounded by a thin disk accretion. For a four-dimensional ABG black hole, as the charge q increases, the event horizon r₊, radius r_p and impact parameter b_p of the photon sphere decrease, while the maximum value of effective potential V_eff increases. However, as the term γ associated with nonlinear electrodynamics increases, the related physical quantities r₊, r_p and b_p increase, but the maximum value of V_eff decreases. When the light ray reaches the vicinity of the ABG black hole, one can observe the trajectories of the light rays appearing as three types, i.e., direct emission, lens ring and photon ring. Furthermore, the shadows and the observational appearance of the ABG black hole are studied. The results show that the charge q and the term γ have a great influence on the shape and intensity of the black hole shadow. When the relevant state parameters change or the emission model changes, it can be argued that it is the direct emission that plays a decisive role in the total observed intensity of the ABG black hole, while the contribution of the lens ring to the total observed intensity is small and the photon ring makes almost no contribution.     

Exact solutions to the angular Teukolsky equation with s ≠ 0

We first convert the angular Teukolsky equation under the special condition of τ ≠ 0, s ≠ 0, m=0 into a confluent Heun differential equation (CHDE) by taking different function transformation and variable substitution. And then according to the characteristics of both CHDE and its analytical solution expressed by a confluent Heun function (CHF), we find two linearly dependent solutions corresponding to the same eigenstate, from which we obtain a precise energy spectrum equation by constructing a Wronskian determinant. After that, we are able to localize the positions of the eigenvalues on the real axis or on the complex plane when τ is a real number, a pure imaginary number, and a complex number, respectively and we notice that the relation between the quantum number l and the spin weight quantum number s satisfies the relation l=∣s∣+ n, n=0, 1, 2···. The exact eigenvalues and the corresponding normalized eigenfunctions given by the CHF are obtained with the aid of Maple. The features of the angular probability distribution (APD) and the linearly dependent characteristics of two eigenfunctions corresponding to the same eigenstate are discussed. We find that for a real number τ, the eigenvalue is a real number and the eigenfunction is a real function, and the eigenfunction system is an orthogonal complete system, and the APD is asymmetric in the northern and southern hemispheres. For a pure imaginary number τ, the eigenvalue is still a real number and the eigenfunction is a complex function, but the APD is symmetric in the northern and southern hemispheres. When τ is a complex number, the eigenvalue is a complex number, the eigenfunction is still a complex function, and the APD in the northern and southern hemispheres is also asymmetric. Finally, an approximate expression of complex eigenvalues is obtained when n is greater than ∣s∣.     

二维圆盘颗粒体系声学行为的数值研究

数值测量了卸载过程中二维单分散圆盘颗粒系统的横波、纵波声速、声衰减系数、非线性系数随压强的变化以及声衰减系数随频率的变化.结果表明,二维(2D)圆盘颗粒体系的横波、纵波声速均随压强呈分段幂律标度:当压强P10~(-4)时,横波、纵波声速随压强的增大而减小;当P10~(-4)时,有v_t~P~(0.202),v_l~P~(0.338).进一步得到其剪切模量和体积模量的比值G/B也随压强呈幂律标度,G/B~P~(-0.502),暗示在低压强下,与三维(3D)球形颗粒体系类似,2D圆盘颗粒体系也处于L玻璃态.水平激励和垂直激励下2D圆盘颗粒系统的衰减系数随频率变化也呈现分段行为:当频率f0.05时,衰减系数不随f变化;当f0.05时,横波纵波的衰减系数α~f;当f0.35时,横波衰减系数α_T~f~2,纵波衰减系数α_L~f~(1.5).此外,竖直水平激励下的2D圆盘颗粒系统的非线性系数和衰减系数随压强也呈现与声速类似的分段规律:当P10~(-4)时,横波非线性系数β_T~P~(-0.230),其余都不随压强变化.当P10~(-4)时,两者均随压强增大呈幂律减小:β_T~P~(-0.703),β_L~P~(-0.684),α_T~P~(-0.099),α_L~P~(-0.105).进而得到2D圆盘颗粒系统中散射相关的特征长度?~*随压强呈幂律标度,当P10~(-4)时,?~*~P~(-0.595);当P10~(-4)时,?~*~P~(0.236).     

Shape coexistence in 76Se within the neutron–proton interacting boson model

We have investigated the low-lying energy spectrum and electromagnetic transition strengths in even–even ⁷⁶Se using the proton–neutron interacting boson model (IBM-2). The theoretical calculation for the energy levels and E2 and M1 transition strengths is in good agreement with the experimental data. Specifically, the excitation energy and E2 transition of ${0}_{2}^{+}$ state, which is intimately associated with shape coexistence, can be accurately reproduced. The analysis on low-lying states and the key structure indicators R₁, R₂, R₃ and R₄ and M1 transitions indicates that there is a coexistence between spherical shape and γ-soft shape in ⁷⁶Se.     

Joule–Thomson expansion of RN-AdS black hole immersed in perfect fluid dark matter

In this paper, we study the Joule–Thomson expansion for RN-Ad S black holes immersed in perfect fluid dark matter. As perfect fluid dark matter is one of the dark matter candidates, we are interested in how it influences the thermodynamic properties of black holes. Firstly, the negative cosmological constant could be interpreted as thermodynamic pressure and its conjugate quantity as the thermodynamic volume, which give us more physical insights into the black hole. Moreover, we derive the thermodynamic definitions and study the critical behaviour of the black hole. Secondly,the explicit expression of Joule–Thomson coefficient is obtained from the basic formulas of the pressure, the volume, the entropy and the temperature. Then, we obtain the inversion curves in terms of charge Q and parameter λ. Furthermore, we analyse the isenthalpic curve in T–P graph with the cooling–heating region determined by the inversion curve. At last, we derive the ratio of minimum inversion temperature to critical temperature and compare the result with that in the RN-Ad S case.     

Single-photon quantum router based on asymmetric intercavity couplings

As a special quantum node in a quantum network, the quantum router plays an important role in storing and transferring quantum information. In this paper, we propose a quantum router scheme based on asymmetric intercavity couplings and a three-level Λ-type atomic system. This scheme implements the quantum routing capability very well. It can perfectly transfer quantum information from one quantum channel to another. Compared with the previous quantum routing scheme, our proposed scheme can achieve the transfer rate of single photons from one quantum channel to another quantum channel reaching 100%, the high transfer rate is located in the almost quadrant regions with negative values of the two variables λ_a and λ_b, and their maximum values T_u~b+T_d~b= 1 emerge in the center point λ_a=λ_b=-1. Therefore, it is possibly feasible to efficiently enhance the routing capability of the single photons between two channels by adjusting the inter-resonator couplings, and the asymmetric intercavity coupling provides a new method for achieving high-fidelity quantum routers.     

Study of semileptonic decay of ${\bar{B}}_{s}^{0} \rightarrow \phi {l}^{+}{l}^{-}$ in QCD sum rule

In this work we study the semileptonic decay of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) with the QCD sum rule method. We calculate the ${\bar{B}}_{s}^{0}\to \phi $ translation form factors relevant to this semileptonic decay, then the branching ratios of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) decays are calculated with the form factors obtained here. Our result for the branching ratio of ${\bar{B}}_{s}^{0}\to \phi {\mu }^{+}{\mu }^{-}$ agree very well with the recent experimental data. For the unmeasured decay modes such as ${\bar{B}}_{s}^{0}\to \phi {e}^{+}{e}^{-}$ and ${\bar{B}}_{s}^{0}\to \phi {\tau }^{+}{\tau }^{-}$, we give theoretical predictions.     

Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles

We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2 nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300 K under zero external DC field for frequencies ranging from f=10 to 10,000 Hz. A prominent peak appears in both χ′ and χ″ as a function of T. The peak temperature T₂ of χ″ depends on f following the Vogel–Fulcher law. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at T_B^m94 K in ZFC and 119 K in AC susceptibility measurements, respectively, which depends on the applied field. The saturation magnetization and the coercivity measured at 4.2 K are 27.3 emu/g and 14.7 kOe, respectively. The particle size distribution was determined by fitting a magnetization curve obtained at 295 K assuming a log-normal size distribution. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy, K=6×10⁶ erg/cm³. Mössbauer spectra obtained at higher temperatures show a gradual collapse of the magnetic hyperfine splitting typical for superparamagnetic relaxation. At 4.2 K, the Mössbauer spectrum was fitted with two magnetic subspectra with internal fields H_int of 490, 470 and 515 kOe, corresponding to Fe³⁺ ions in A and B sites.     

Study of the XYZ states at the BESIII

With its unique data samples at energies of 3.8–4.6 GeV, the BESIII experiment made a significant contribution to the study of charmonium and charmonium-like states, i.e., the XYZ states.We review the results for observations of the Z_c(3900) and Z_c(4020) states, the X(3872) in e⁺e⁻ annihilation, and charmonium ψ(1³D₂) state, as well as measurements of the cross-sections of ωχ_cJ and ηJ/ψ, and the search for e⁺e⁻→ γχ_cJ and γY (4140). We also present data from BESIII that may further strengthen the study of the XYZ and conventional charmonium states, and discuss perspectives on future experiments.     

分离压作用下波纹状基底上含活性剂液滴铺展稳定性

针对波纹状基底上含不溶性活性剂液滴的铺展过程,引入受活性剂浓度影响的分离压模型,应用非模态稳定性理论分析液滴铺展稳定性.研究表明:与不计及分离压情形相比,分离压作用下的液滴铺展前沿高度明显下降,液滴铺展速率加快;长波扰动有利于增强液滴的演化稳定性,且随扰动波数增大稳定性增强;然而随短波波数增加,液滴演化稳定性逐渐减弱甚至转变为不稳定;较小波数下(k=3)减小引力强度系数α₁和提高斥力强度系数α₂液滴铺展稳定性增强;而较大波数下(k=30)增大α₁和减小α₂有利于液滴铺展稳定性.