Refraction in spacetime

Refraction, interference, and diffraction serve as distinguishing features for wave-like phenomena. While they are normally associated only with a purely spatial wave-propagation pattern, analogs to interference and diffraction involving the spatio-temporal dynamics of waves in one dimension (1D) have been pointed out. Here we complete the triplet of analogies by discussing how spatio-temporal analogs to refraction are exhibited by a quantum particle in 1D that is scattering off a step barrier. Similarly, birefringence in spacetime occurs for a spin-1/2 particle in a magnetic field. These examples serve to illustrate basics of quantum time evolution from a new perspective.