Bose-Einstein condensation: where many become one and so there is plenty of room at the bottom

Abstract

Bose-Einstein condensation and superfluidity are well known to occur in the dilute gaseous as well as in the dense liquid state of matter having a fixed number of Bose particles. Very recently, experimental evidence has been obtained for the probable realization of BEC and superfluidity in ⁴He in the solid state too, as revealed through its non-classical rotational moment of inertia-smaller than that for the solid. Such a solid that can also subtend a flow as superfluid- and hence a supersolid-is indeed a surprise of condensed matter physics. In this conversation, an order-parameter description for the supersolid state will be given in which the superfluid flow is decoupled from the crystalline density modulation which remains at rest in the laboratory frame, thus giving it a nonclassical inertia.