Enhancing Parameter Estimation Precision in a Dissipative Environment with Two-Photon Driving

The frequency estimation of an optical cavity field suffering from an unavoidable dissipative environment is investigated. Generally, dissipative noise significantly reduces the precision. Here, it is found that two-photon driving can improve measurement precision by resisting the noise. Moreover, over a long duration, the frequency uncertainty can be minimized with the right magnitude of the parametric two-photon drive, which is in sharp contrast to the uncertainty tending to infinity without two-photon driving. The results show that two-photon driving can achieve ultrasensitive measurement in a dissipative environment under the long-encoding-time condition.     

Nonequilibrium Effects on the Precision of Parameter Estimation

The impact of nonequilibrium environment effects on the accuracy of quantum parameter estimation is investigated, and it is found that these effects can significantly affect estimation accuracy. Using an individual estimation strategy reveals that the nonequilibrium effects consistently enhance accuracy, regardless of the coupling strength between the probe and its environment. In contrast, weak memory effects undermine estimation accuracy. When employing a multi-parameter simultaneous estimation strategy, it is observed that the nonequilibrium effects consistently improve the advantages of simultaneous estimation, as analyzed by the ratio of total variances between the two estimation scenarios. However, the memory effects on these advantages depend on the coupling strength between the qubit and the environment. These findings suggest that appropriate parameters of a nonequilibrium environment can increase the quantum Fisher information (QFI), thereby enhancing the accuracy of quantum parameter estimation. These significant results are essential for improving parameter estimation accuracy in quantum systems interacting with nonequilibrium environments.     

一个评价光谱估计精度的新参数

研究了对多光谱成像系统进行光谱估计的精度评价的问题。在给出光谱估计偏指数定义的基础上,提出了多光谱图像获取系统的光谱估计性能的评价的新方法——系统光谱匹配偏度指数法。该方法用一个指标来定量评价两光谱向量的光谱匹配程度,避免了以往评价参数的复杂性,同时反映了光谱反射率估计曲线实际测量曲线之间的差异程度。采用一典型多光谱相机对Macbeth色卡的24个典型光谱仿真估计所得的24个光谱对数值模拟,验证了光谱反射率估计匹配偏度指数能全面的反映光谱反射率的估计精度的设想;并拿17个多光谱估计系统的仿真估计的光谱数据,计算了它们的系统光谱估计偏度指数,计算结果有很好的一致性。结果还显示,系统光谱估计偏度指数还可用作对多光谱相机光谱估计性能进行等级划分的依据。     

The Precision of Parameter Estimation for Dephasing Model Under Squeezed Reservoir

We study the precision of parameter estimation for dephasing model under squeezed environment. We analytically calculate the dephasing factor γ(t) and obtain the analytic quantum Fisher information (QFI) for the amplitude parameter α and the phase parameter ?. It is shown that the QFI for the amplitude parameter α is invariant in the whole process, while the QFI for the phase parameter ? strongly depends on the reservoir squeezing. It is shown that the QFI can be enhanced for appropriate squeeze parameters r and θ. Finally, we also investigate the effects of temperature on the QFI.     

利用纠缠密度研究光子禁带系统的纠缠演化特性

研究了一个二能级原子在光子禁带模型中的原子与热库间及热库模式间的纠缠动力学行为.利用全局纠缠的方法,引出与热库模式相关的纠缠密度.研究发现,当禁带是完美带隙时,会出现稳态原子布居数俘获现象,从而抑制原子的自发辐射效应,防止了信息传输过程中信息的流失.原子与热库模式之间的纠缠密度以及热库模式与模式之间的纠缠密度会随着原子与热库之间耦合强度的增加而增大.当取长时极限时,原子与热库模式之间的纠缠减为零.热库模式与模式之间在强耦合情况下,由于拉比分裂的作用,在两个对称模式间会形成较强的纠缠;在弱耦合情况下,只能在中心频率处形成纠缠.     

微波段左手材料光子晶体带隙特性研究

利用电磁理论和传输矩阵法仿真得到了在0.3~6.935GHz微波波段具有负折射率的左手材料,并分别对右手材料和左手材料构成的光子晶体带隙特点进行了分析.结果表明:右手材料光子晶体结构的带隙对周期数变化不敏感,而对层厚度比、入射角度变化敏感;左手材料光子晶体带隙随层厚度比的增大,带隙位置出现蓝移,随着入射角度的增大,TM波主带隙的上带边会出现红移,而TE波带隙特性对入射角度变化不敏感.研究结果对微波技术中全方位反射器等器件的设计有一定的参考意义.     

一维光子晶体禁带特性的研究

应用传输矩阵法研究了一维光子晶体的禁带特性,数值模拟得到了一维光子晶体TE模、TM模和TE/TM模禁带结构,计算结果表明,介质层的厚度发生变化时,禁带宽度发生变化。研究结果为一维光子晶体器件的设计提供了理论依据。     

一维光子晶体禁带的展宽

作为一维光子晶体的应用基础，一维光子晶体的禁带是研究的重点。通过传输矩阵的方法分析了一维光子晶体禁带的特性，讨论了影响带宽的因素。说明了相对带宽对光子晶体设计的重要性。在这个基础上讨论了扩展一维光子晶体带宽的方法，提出了在角域范围内对光子晶体进行叠加的方法，为设计制造一维光子晶体提供了一种行之有效的方法。分别对2个、3个和4个晶体的叠加进行了分析，最后计算了所设计的合成晶体的反射率。其中4个晶体的叠加，相对带宽达到57．52％，极大地展宽了一维光子晶体的禁带，从而证明利用角域的叠加来展宽一维光子晶体的禁带是非常有效的。     

Estimation of Precision of Determining the Yarkovsky Effect Parameter Based on Real and Model Observations of Asteroids

Russian Physics Journal - The paper presents results of evaluating the precision of determining the Yarkovsky effect parameter A2 for asteroids with small perihelion distances known by January...     

Band Gap Modulation by Two-Dimensional h-BN Nanostructure

Physics of the Solid State - Two-dimensional hexagonal boron nitride (h-BN) as a graphene-like material was investigated due to its impending applications in electronics. The h-BN band gap Eg as an...     

Modification of Band Gap of -SiC by N-Doping

The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx （x = 0, 1/32, 1/16, 1/8, 1/4） with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.     

蜂巢晶格光子晶体能带特性的研究

运用时域有限差分法数值模拟了蜂巢晶格光子晶体能带特性,得到了蜂巢晶格光子晶体的最大横电(TE)模、横磁(TM)模和完全带隙,研究结果为光子晶体器件的开发提供了理论依据.     

Ground State and Band Gap of MX complex

Using the one-band model of halogen-bridged mixed-valence transition metal complex (MX complex), within mean field theory, we have proved for fixed electron-phonon coupling, the band gap reaches the minimum at the boundary of the charge density wave state and the spin density wave state in the phase diagram. The analytic form of the ground state energy and the band gap are also obtained.     

Recent Emission Channeling Studies in Wide Band Gap Semiconductors

We present results of recent emission channeling experiments on the lattice location of implanted Fe and rare earths in wurtzite GaN and ZnO. In both cases the majority of implanted atoms are found on substitutional cation sites. The root mean square displacements from the ideal substitutional Ga and Zn sites are given and the stability of the Fe and rare earth lattice location against thermal annealing is discussed.     

A Novel Approach for the Evaluation of Band Gap Energy in Semiconductors

On the basis of absorption nature of semiconductors, we present a novel and simple method to determine the band gap energies of semiconductors directly from their absorption spectra at any temperatures, without any fitting processes and restrictions of sample thickness. The key point of the approach is the different dependence of the absorption coefficient derivative on the photon energy at different absorption regions in semiconductors. We first demonstrate and verify the approach by detailed temperature-dependent absorption measurements, combined with photoluminescence measurements and empirical band gap equations for the direct band gap of uniform InAs films, and then extend successfully to the indirect band gap of elemental Ge and to the ternary HgCdTe alloys with composition gradient. Furthermore, we have also shown that our approach can not only evaluate the average band gap energy for ternary semiconductor alloys, but also estimate their composition uniformity to monitor the material quality.     

体积全息图中光子禁带结构性质的分析

利用光子晶体的概念和方法，从理论上分析了一维全息图在再现光以不同角度入射情况下禁带结构的性质。分析表明，当再现光非正入射时，体积全息图的禁带结构是倾斜的，正入射时的非倾斜结构是倾斜结构的一个特例。     

光子晶体带隙和缺陷的特性

基于平面波展开法,以介电常数分别为1F/m和13F/m的物质构成三角晶格二维光子晶体,改变空气孔半径r与晶格常数a之间的大小,数值模拟得到r=0.48a时形成最大完全带隙0.4298-0.5192Hz.移去中心圆柱形成缺陷,数值模拟得到不能形成完全带隙结构,研究结论为光子晶体器件的制作提供参考.