Propagation of a gaussian wavepacket in a 2D box. In agreement with the Ehrenfest theorem, the wavepacket center moves like a classical particle, boucing on the walls of the box. Quantum mechanics manifests itself through the interferences between the incident and reflected waves, and through the spreading of the wavepacket, similarly to what we observed in one dimension.
NB: The parameters of the simulation are not quite right. In reality, such a wavepacket would need a much smaller value of the wavelength in order to spread so slowly. The size of the wavelength has been enlarged so that interferences could be seen on such a low-resolution image.