Quantum reflection by coupled-channel potentials

We study quantum reflection in a system of two attractive step potentials with a steplike coupling term. The amplitude R11 for elastic reflection generally has the near-threshold behavior |R11|k→0∼1-2bk familiar from the single-channel case. Reflectivity in the elastic channel is quenched in the presence of a second adiabatic channel open for transmission, while it is enhanced when the second transmission channel is closed; there is a pronounced minimum in the reflectivity when the potential in the upper adiabatic channel is zero or close to zero. When the upper adiabatic channel is repulsive, the elastic reflectivity can have an exact zero, at which quantum reflection leads to complete transfer into the excited state. Any degree of entanglement of translational and internal motion can be achieved at an appropriate energy between the threshold for inelastic reflection and this zero of the elastic reflectivity. For degenerate reflection channels, the unusual case of incomplete reflection at threshold occurs when the potential in the upper adiabatic channel vanishes