Quantum Mechanics: Concepts and Applications · Problem 5.16

Three-Dimensional Problems — Nouredine Zettili

Physics — Quantum Mechanics · angular-momentum-state-expectation

Problem

Consider a system which is described by the state ψ(θ, φ)=38Y11(θ, φ)+18Y10(θ, φ)+AY1,−1(θ, φ),\psi(\theta,\ \varphi) = \sqrt{\frac{3}{8}}Y_{11}(\theta,\ \varphi) + \sqrt{\frac{1}{8}}Y_{10}(\theta,\ \varphi) + AY_{1,-1}(\theta,\ \varphi), where AA is a real constant. (a) Calculate AA so that ∣ψ⟩|\psi\rangle is normalized. (b) Find L^+ψ(θ, φ)\hat{L}_+\psi(\theta,\ \varphi). (c) Calculate the expectation values of L^x\hat{L}_x and L^2\hat{L}^2 in the state ∣ψ⟩|\psi\rangle. (d) Find the probability associated with a measurement that gives zero for the zz-component of the angular momentum. (e) Calculate ⟨Φ∣L^z∣ψ⟩\langle \Phi|\hat{L}_z|\psi\rangle and ⟨Φ∣L^−∣ψ⟩\langle \Phi|\hat{L}_-|\psi\rangle where Φ(θ, φ)=815Y11(θ, φ)+415Y10(θ, φ)+315Y2,−1(θ, φ).\Phi(\theta,\ \varphi) = \sqrt{\frac{8}{15}}Y_{11}(\theta,\ \varphi) + \sqrt{\frac{4}{15}}Y_{10}(\theta,\ \varphi) + \sqrt{\frac{3}{15}}Y_{2,-1}(\theta,\ \varphi).

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