Momentum-dependent pseudospin dimers of coherently coupled bosons in optical lattices

We study the two-body bound and scattering states of two particles in a one-dimensional optical lattice in the presence of a coherent coupling between two internal atomic levels. Due to the interplay between periodic potential, interactions, and coherent coupling, the internal structure of the bound states depends on their center-of-mass momentum. This phenomenon corresponds to an effective momentum-dependent magnetic field for the dimer pseudospin, which could be observed in a chirping of the precession frequency during Bloch oscillations. The essence of this effect can be easily interpreted in terms of an effective bound-state Hamiltonian. Moreover for indistinguishable bosons, the two-body eigenstates can present simultaneously attractive and repulsive bound-state natures or even bound and scattering properties.