Quantum bifurcations and quantum phase transitions in rotational spectra

An interconnection between quantum bifurcations and quantum phase transitions is investigated. It is shown that the quantum phase transition is the limiting case of the quantum bifurcation in macroscopic systems. Critical phenomena in microscopic many-body systems such as nuclei and molecules are described by quantum bifurcations. They are characterized by a large transition region, which conceals a critical point. Both the quantum bifurcation and quantum phase transition show that a change in the internal structure of a system manifests itself in the modification of its rotational spectrum. Such an intimate connection between internal and rotational motion allows a critical phenomenon to be established.