  Quantum transients are temporary features of matter waves before they reach a
stationary regime. Transients may arise after the preparation of an unstable
initial state or due to a sudden interaction or a change in the boundary
conditions. Examples are diffraction in time, buildup processes, decay,
trapping, forerunners or pulse formation, as well as other phenomena recently
discovered, such as the simultaneous arrival of a wave peak at arbitrarily
distant observers. The interest on these transients is nowadays enhanced by new
technological possibilities to control, manipulate and measure matter waves.
