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Solutions to Principles of Quantum Mechanics
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Chapter 12 Rotational Invariance and Angular Momentum

12.1 Translations in Two Dimensions

Exercise 12.1.1 Verify that a^P\hat{a} \cdot \mathbf{P} is the generator of infinitesimal translations along a by considering the relation

x,yIiδaPψ=ψ(xδax,yδay)\langle x, y| I-\frac{i}{\hbar} \boldsymbol{\delta} a \cdot \mathbf{P}|\psi\rangle=\psi\left(x-\delta a_x, y-\delta a_y\right)
2025-05-30
Solutions to Principles of Quantum Mechanics
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Chapter 11 Symmetries and Their Consequences

11.1 Overview

11.2 Translational Invariance in Quantum Theory

Exercise 11.2.1 Verify Eq. (11.2.11b).

2025-05-30
Solutions to Principles of Quantum Mechanics
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Chapter 10 Systems with NN Degrees of Freedom

10.1 NN Particles in One Dimension

Exercise 10.1.1 Show the following:

(1)

[Ω1(1)I(2),I(1)Λ2(2)]=0 for any Ω1(1) and Λ2(2)(10.1.17a)[\Omega_{1}^{(1)}\otimes I^{(2)}, I^{(1)}\otimes \Lambda_{2}^{(2)}]=0~\text{for any}~\Omega_{1}^{(1)}~\text{and}~\Lambda_{2}^{(2)}\tag{10.1.17a}

(2)

(Ω1(1)Γ2(2))(θ1(1)Λ2(2))=(Ωθ)1(1)(ΓΛ)2(2)(10.1.17b)(\Omega_{1}^{(1)}\otimes\Gamma_{2}^{(2)})(\theta_{1}^{(1)}\otimes\Lambda_{2}^{(2)})=(\Omega\theta)_{1}^{(1)}\otimes(\Gamma\Lambda)_{2}^{(2)}\tag{10.1.17b}

(3)If

[Ω1(1),Λ1(1)]=Γ1(1)[\Omega_{1}^{(1)},\Lambda_{1}^{(1)}]=\Gamma_{1}^{(1)}

then

[Ω1(1)(2),Λ1(1)(2)]=Γ1(1)I(2)(10.1.17c)[\Omega_{1}^{(1)\otimes(2)},\Lambda_{1}^{(1)\otimes(2)}]=\Gamma_{1}^{(1)}\otimes I^{(2)}\tag{10.1.17c}

and similarly with 121\to 2.

(4)

(Ω1(1)(2)+Ω2(1)(2))2=(Ω12)(1)I(2)+I(1)(Ω22)(2)+2Ω1(1)Ω2(2)(10.1.17d)(\Omega_{1}^{(1)\otimes (2)}+\Omega_{2}^{(1)\otimes(2)})^{2}=(\Omega_{1}^{2})^{(1)}\otimes I^{(2)}+I^{(1)}\otimes (\Omega_{2}^{2})^{(2)}+2\Omega_{1}^{(1)}\otimes\Omega_{2}^{(2)}\tag{10.1.17d}
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Chapter 9 The Heisenberg Uncertainty Relations

9.1 Introduction

9.2 Derivation of the Uncertainty Relations

9.3 The Minimum Uncertainty Packet

9.4 Applications of the Uncertainty Principle

Exercise 9.4.1 Consider the oscillator in the state n=1|n=1\rangle and verify that

1X21X2mω\left\langle\frac{1}{X^2}\right\rangle \simeq \frac{1}{\left\langle X^2\right\rangle} \simeq \frac{m \omega}{\hbar}
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Solutions to Principles of Quantum Mechanics
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Chapter 8 The Path Integral Formulation of Quantum Theory

8.1 The Path Integral Recipe

8.2 Analysis of the Recipe

8.3 An Approximation to U(t)U(t) for the Free Particle

8.4 Path Integral Evaluation of the Free-Particle Propagator

8.5 Equivalence to the Schrödinger Equation

8.6 Potentials of the Form V=a+bx+cx2+dx˙+exx˙V=a+bx+cx^{2}+d\dot{x}+ex\dot{x}

Exercise 8.6.1 Verify that

U(x,t;x,0)=A(t)exp(iScl/), A(t)=(m2πit)1/2U(x,t;x^{\prime},0)=A(t)\exp(\mathrm{i}S_{\text{cl}}/\hbar),~A(t)=\left(\dfrac{m}{2\pi\hbar\mathrm{i}t}\right)^{1/2}

agrees with the exact result, Eq. (5.4.31), for V(x)=fxV(x)=-fx. Hint: Start with xcl(t)=x0+v0t+12(f/m)t2x_{\text{cl}}(t^{\prime\prime})=x_{0}+v_{0}t^{\prime\prime}+\dfrac{1}{2}(f/m)t^{\prime\prime 2} and find the constants x0x_{0} and v0v_{0} from the requirement that xcl(0)=xx_{\text{cl}}(0)=x^{\prime} and xcl(t)=xx_{\text{cl}}(t)=x.