Isolated States

We show that a quantum system with nonlocal interaction can have bound states of unusual type (isolated states (IS)). IS is a bound state that do not generate a $S$-matrix pole. IS can have positive as well as negative energy and can be treated as a generalization of bound states embedded in continuum on the case of discrete spectrum states. Formation of IS in the spectrum of quantum system is studied using a simple rank--2 separable potential with harmonic oscillator formfactors. Some physical applications are discussed, in particular, we propose separable $NN$ potential that describes not only most important two-nucleon data (deuteron binding energy and s-wave triplet and singlet scattering phases) but also the trinucleon binding energy without making use of three-body forces.