The nature of superfluidity and Bose-Einstein condensation: From liquid 4He to dilute ultracold atomic gases (Review Article)

We present a brief overview of crucial historical stages in creation of superfluidity theory and of the current state of the microscopic theory of superfluid He-4. We pay special attention to the role of Bose-Einstein condensates (BECs) in understanding of physical mechanisms of superfluidity and identification of quantum mechanical structure of He-4 superfluid component below lambda-point, in particular-the possibility that at least two types of condensates may appear and coexist simultaneously in superfluid He-4. In this context we discuss the properties of the binary mixtures of BECs and types of excitations, which may appear due to intercomponent interaction in such binary mixtures of condensates. We also discuss current status of investigations of persistent currents in toroidal optical traps and present an outlook of our recent findings on this subject. (C) 2013 AIP Publishing LLC.