The creation of tunable open quantum systems is becoming feasible in current
experiments with ultracold atoms in low-dimensional traps. In particular, the
high degree of experimental control over these systems allows detailed studies
of tunneling dynamics, e.g., as a function of the trapping geometry and the
interparticle interaction strength. In order to address this exciting
opportunity we present a theoretical framework for two-body tunneling based on
the rigged Hilbert space formulation. In this approach, bound, resonant and
scattering states are included on an equal footing, and we argue that the
coupling of all these components is vital for a correct description of the
relevant threshold phenomena. In particular, we study the tunneling mechanism
for two-body systems in one-dimensional traps and different interaction
regimes. We find a strong dominance of sequential tunneling of single particles
for repulsive and weakly attractive systems, while there is a signature of
correlated pair tunneling in the calculated many-particle flux for strongly
attractive interparticle interaction.Comment: To be published in Phys. Rev. A (Rapid Communication
