Quantum Mechanics: Concepts and Applications · Problem 5.9

Three-Dimensional Problems — Nouredine Zettili

Physics — Quantum Mechanics · orbital-angular-momentum-spherical-harmonics

Problem

Consider a system which is initially in the state ψ(θ, φ)=15Y1,−1(θ, φ)+35Y10(θ, φ)+15Y11(θ, φ).\psi(\theta,\ \varphi) = \frac{1}{\sqrt{5}}Y_{1,-1}(\theta,\ \varphi) + \sqrt{\frac{3}{5}}Y_{10}(\theta,\ \varphi) + \frac{1}{\sqrt{5}}Y_{11}(\theta,\ \varphi). (a) Find ⟨ψ∣L^+∣ψ⟩\langle \psi | \hat{L}_+ | \psi \rangle. (b) If L^z\hat{L}_z were measured what values will one obtain and with what probabilities? (c) If after measuring L^z\hat{L}_z we find lz=−ℏl_z = -\hbar, calculate the uncertainties ΔLx\Delta L_x and ΔLy\Delta L_y and their product ΔLxΔLy\Delta L_x \Delta L_y.

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