  We study theoretically the interaction between two species of ultracold atoms
confined into two layers of a finite separation, and demonstrate the existence
of new types of confinement-induced interlayer bound and quasi-bound molecules:
these novel exciton-like interlayer molecules appear for both positive and
negative scattering lengths, and exist even for layer separations many times
larger than the interspecies scattering length. The lifetime of the quasi-bound
molecules grows exponentially with increasing layer separation, and they can
therefore be observed in simple shaking experiments, as we demonstrate through
detailed many-body calculations. These quasi-bound molecules can also give rise
to novel interspecies Feshbach resonances, enabling one to control
geometrically the interaction between the two species by changing the layer
separation. Rather counter-intuitively, the species can be made strongly
interacting, by increasing their spatial separation. The separation induced
interlayer resonances provide a powerful tool for the experimental control of
interspecies interactions and enables one to realize novel quantum phases of
multicomponent quantum gases.
