  A simple theory for the tunneling of two cold atoms out of a trap in the
presence of an attractive contact force is developed. Two competing decay
channels, respectively for single-atom and bound-pair tunneling, contribute
independently to the decay law of the mean atom number in the trap. The
single-atom tunneling rate is obtained through the quasiparticle wave function
formalism. For pair tunneling an effective equation for the center-of-mass
motion is derived, so the calculation of the corresponding tunneling rate is
again reduced to a simpler one-body problem. The predicted dependence of
tunneling rates on the interaction strength qualitatively agrees with a recent
measurement of the two-atom decay time [G. Zuern, A. N. Wenz, S. Murmann, T.
Lompe, and S. Jochim, arXiv:1307.5153].
