Coherence and superfluidity are hallmark properties of quantum fluids and encompass a whole class of fundamental phenomena. With the achievement of Bose-Einstein condensation in atomic gases, it became possible to study these phenomena in a clean and well controlled environment, where the atomic sample is maintained at sub-microKelvin temperature, and is acted upon using only electromagnetic fields.

The talk will review the physical origin and the experimental evidences of these remarkable coherence properties of quantum gases, and it will discuss the analogies and differences between these and other well known macroscopic quantum systems, such as superfluid liquid helium or supraconducting materials. It will then focus on the spectacular properties of rotating condensates in which a macroscopic flow can be generated through the nucleation of quantized vortices.

Photo: Nucleation of quantized vortices in a gaseous condensate stirred with a laser beam.