Measurement Values for z-component of Angular Momentum

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SUMMARY

The discussion focuses on calculating the expectation value of the z-component of angular momentum for a given wave function $$\Psi(r,\theta,\phi)=f(r)\sin^2(\theta)(2\cos^2(\phi)-1-2i*\sin(\phi)\cos(\phi))$$. Participants explored the integral formula $$<\hat L_z> = \iiint\Psi^*(\hat L_z)\Psi dV$$, where $$\hat L_z=-i\hbar (\frac{\partial}{\partial \phi})$$ and $$dV=r^2\sin(\theta)drd\theta d\phi$$. The complexity of the integral raised concerns about the validity of the approach. Suggestions included considering the wave function as a superposition of eigenfunctions of $$L_z$$ and familiarizing oneself with low-order spherical harmonics.

PREREQUISITES
  • Understanding of wave functions in quantum mechanics
  • Familiarity with angular momentum operators, specifically $$\hat L_z$$
  • Knowledge of spherical coordinates and volume elements in three dimensions
  • Basic understanding of spherical harmonics and their properties
NEXT STEPS
  • Study the properties of spherical harmonics and their role in quantum mechanics
  • Learn how to compute expectation values for angular momentum using different wave functions
  • Explore the concept of superposition in quantum states and its implications for angular momentum
  • Investigate alternative methods for evaluating complex integrals in quantum mechanics
USEFUL FOR

Quantum mechanics students, physicists working on angular momentum problems, and researchers interested in wave function analysis will benefit from this discussion.

MoAli
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Given a wave function $$\Psi(r,\theta,\phi)=f(r)\sin^2(\theta)(2\cos^2(\phi)-1-2i*\sin(\phi)\cos(\phi))$$ we are trying to find what a measurement of angular momentum of a particle in such wave function would yield.
Attempts were made using the integral formula for the Expectation Value over a spherical volume: $$<\hat L_z> = \iiint\Psi^*(\hat L_z)\Psi dV$$ where $$dV=r^2\sin(\theta)drd\theta d\phi$$ and $$\hat L_z=-i\hbar (\frac{\partial}{\partial \phi} ).$$ The Integral seemed really difficult to clear up and get a valid expression, which caused a doubt about whether the approach is incorrect in the first place. Any suggestions on an efficient or smarter way of approaching those types of problems?
Thank you!
 
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It's more useful if you try to think the wavefunction you are given with as a superposition of eigenfunctions of ##L_z##. At the same time try to get familiar with some low order spherical harmonics (e.g. in https://en.wikipedia.org/wiki/Table_of_spherical_harmonics) and recognize how they typically depend on the angles ##\theta## and ##\phi## for a given pair of ##l## and ##m##.
 

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