Condensed matter provides us deep insights into quantum physics.
Giving just two examples, wave-corpuscle duality manifests itself in
spectroscopy of strongly correlated systems as coexistence of itinerant
and atomic-like features, and graphene and other Dirac materials
provide a natural playground to study vacuum reconstruction, Klein
tunneling and other fundamental quantum relativistic phenomena.
Electron-photon interaction is the key tool to understand this rich
and nontrivial physics.