  We study the quantum mechanical motion of massive particles in a system of
two coupled waveguide potentials, where the population transfer between the
waveguides effectively acts as a clock and allows particle velocities to be
determined. Application of this scheme to evanescent phenomena at a reflective
step potential reveals an energy-velocity relationship for classically
forbidden motion. Regions of gain and loss, as described by imaginary
potentials, are shown to speed up the motion of particles. We argue that phase
and density gradients in quantum mechanical wave functions play complementary
roles in indicating the speed of particles.
