Entanglement in a model of inelastic spectroscopy

The treatment of a quantum harmonic oscillator excited by an external classical beam is embedded in the physics curriculum, and it is straightforward to obtain probabilities for the beam exciting the oscillator into its various energy eigenstates. Realistic probes, however, are themselves quantum objects, which introduces both pedagogical challenges and opportunities. Treating the harmonic oscillator and external beam each as part of a combined quantum system gives an easily visualized (if less easily calculated) example of entanglement that can augment undergraduate treatments of quantum dynamics, and can provide an additional bridge between wave mechanics and scattering theory.