Posted on Categories:Quantum mechanics, 物理代写, 量子力学

# 物理代写|量子力学代写Quantum mechanics代考|PHYS2941 A Scattering Problem

avatest™

## avatest™帮您通过考试

avatest™的各个学科专家已帮了学生顺利通过达上千场考试。我们保证您快速准时完成各时长和类型的考试，包括in class、take home、online、proctor。写手整理各样的资源来或按照您学校的资料教您，创造模拟试题，提供所有的问题例子，以保证您在真实考试中取得的通过率是85%以上。如果您有即将到来的每周、季考、期中或期末考试，我们都能帮助您！

•最快12小时交付

•200+ 英语母语导师

•70分以下全额退款

## 物理代写|量子力学代写Quantum mechanics代考|A Scattering Problem

As a first example of the connection rules, let us consider a one-dimensional scattering problem in which a particle of energy $E$ comes in from the left, encounters an impenetrable potential barrier, and reflects back to the left. As sketched in Fig. 11, the potential $V(x)$ approaches zero as $x \rightarrow-\infty$ and goes to $\infty$ as $x \rightarrow+\infty$. The particle cannot penetrate the barrier, so all particles launched from the left reflect and go back to the left. The orbit in phase space is illustrated in Fig. 12.

To solve the Schrödinger equation by WKB theory, we observe that the boundary conditions require that the wave function go to zero Region II, so the coefficient of the growing term $c_g$ in this region must be zero. Let us set $c_d=1$ for the coefficient of the damping term in this region, which amounts to a normalization of the wave function overall. Then applying the connection rule (86), we find the coefficients of the right- and left-travelling waves in the classically allowed Region I,
$$\left(\begin{array}{l} c_r \ c_{\ell} \end{array}\right)=\left(\begin{array}{rr} -\frac{i}{2} & 1 \ +\frac{i}{2} & 1 \end{array}\right)\left(\begin{array}{l} 0 \ 1 \end{array}\right)=\left(\begin{array}{l} 1 \ 1 \end{array}\right) .$$
Then Eq. (81) gives the wave function in Region I,
$$\psi_{\mathrm{I}}(x)=\frac{1}{\sqrt{p(x)}}\left(e^{i\left[S\left(x, x_r\right) / \hbar+\pi / 4\right]}+e^{-i\left[S\left(x, x_r\right) / \hbar+\pi / 4\right]}\right)=\frac{2}{\sqrt{p(x)}} \cos \left[\frac{S\left(x, x_r\right)}{\hbar}+\frac{\pi}{4}\right] .$$

## 物理代写|量子力学代写Quantum mechanics代考|An Oscillator

We now apply WKB theory to a one-dimensional bound-state problem. Consider a particle moving in the potential well illustrated in Fig. 13. At the energy $E$, the left turning point is $x_{\ell}$ and the right one is $x_r$. We assume the potential rises to infinity to the left of $x_{\ell}$ and to the right of $x_r$, so no tunnelling out of the well is possible. Region I, $xx_r$, are the classically forbidden regions, while Region II, $x_{\ell}<x<x_r$, is the classically allowed region. Figure 14 shows the orbit $H=E$ in phase space, with arrows indicating the direction of motion.

Let us begin with a somewhat intuitive approach. The particles accumulate a phase $(1 / \hbar) \int p d x$ as they move around the orbit, but lose a phase $\pi / 2$ when passing through a turning point, so on going completely around the orbit and passing through two turning points the total phase is
$$\frac{1}{\hbar} \oint p d x-\pi$$
Notice that $\oint p d x$ is the area in phase space of the orbit. But if the wave function is single-valued, then the phase (102) must be $2 n \pi$, for an integer $n$. Thus we find
$$\oint p d x=\left(n+\frac{1}{2}\right) 2 \pi \hbar$$

## 物理代写|量子力学代写Quantum mechanics代考|A Scattering Problem

(86)，我们找到经典允许的区域 I 中右行波和左行波的系数，
$$\left(c_r c_{\ell}\right)=\left(\begin{array}{lll} -\frac{i}{2} & 1+\frac{i}{2} & 1 \end{array}\right)(01)=(11)$$

$$\psi_{\mathrm{I}}(x)=\frac{1}{\sqrt{p(x)}}\left(e^{i\left[S\left(x, x_r\right) / \hbar+\pi / 4\right]}+e^{-i\left[S\left(x, x_r\right) / \hbar+\pi / 4\right]}\right)=\frac{2}{\sqrt{p(x)}} \cos \left[\frac{S\left(x, x_r\right)}{\hbar}+\frac{\pi}{4}\right]$$

## 物理代写|量子力学代写Quantum mechanics代考|An Oscillator

$$\frac{1}{\hbar} \oint p d x-\pi$$

$$\oint p d x=\left(n+\frac{1}{2}\right) 2 \pi \hbar$$

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。