Student handout: Time Dependence for a Quantum Particle on a Ring Part 1

Central Forces 2021
  • Practice time evolution
  • To calculate quantum probabilities in Dirac and Wavefunction notation
  • To visualize how wave wavefunctions depend on time after time evolution
  • To notice that not all probabilities of operators will depend on time
What students learn
  • Practice time evolution
  • To calculate quantum probabilities in Dirac and Wavefunction notation
  • To visualize how wave wavefunctions depend on time after time evolution
  • To notice that not all probabilities of operators will depend on time

Consider a quantum particle on a ring. At \(t=0\), the particle is in state: \begin{equation*} \left|{\Phi(t=0)}\right\rangle =\frac{7i}{10}\left|{-2}\right\rangle -\frac{1}{2}\left|{-1}\right\rangle +\frac{1}{2}\left|{0}\right\rangle -\frac{1}{10}\left|{2}\right\rangle \end{equation*}

  1. Find \(\left|{\Phi(t)}\right\rangle \)
  2. Calculate the probability that you measure the \(z\)-component of the angular momentum to be \(-2\hbar\) at time \(t\). Is it time dependent?
  3. Calculate the probability that you measure the energy to be \(\frac{2\hbar^2}{I}\) at time \(t\). Is it time dependent?


Author Information
Corinne Manogue, Kerry Browne, Elizabeth Gire, Mary Bridget Kustusch, David McIntyre, Dustin Treece
Keywords
central forces quantum mechanics eigenstates eigenvalues angular momentum time dependence hermitian operators probability degeneracy quantum measurements
Learning Outcomes