Superfluidity and Bose Einstein Condensation Yesterday, Today and Tomorrow

Richard Fitzgerald

Since the early days of Bose–Einstein condensates (BECs) in atomic gases, comparisons have been drawn to the other familiar bosonic systems: liquid helium-4 and the Cooper pairs of superconductors. Two of the early questions asked of BECs were whether they had similar coherence properties and whether they were superfluids. In He4, it is rather difficult to study properties of the condensate, such as the condensate fraction, whereas the measurement of superfluidity is fairly straightforward. The opposite has proved true for atomic condensates: The condensate fraction as a function of temperature was found early on, but only recently has their superfluidity been placed on firm footing (see PHYSICS TODAY, November 1999, page 17).

Bipin R. Desai

Wolfgang Ketterle

Philip Ball

Philip Ball reviews Quantum Steampunk: the Physics of Yesterday’s Tomorrow by Nicole Yunger Halpern.

Kwit Spencer

abstract: While the use of super-cooled gasses as a tool for the study of macroscopic quantum effects has only become experimentally viable in recent years, theories involing such gasses have existed almost as long as quantum theory itself. Albert Einstein first proposed the concept of what is known today as a Bose-Einstein condensate; the driving principle behind his theory was a deliberate exploitation of the symmetric property of multiparticle bosonic wavefunctions. Specifically, since the Bose-Einstein statistics of bosons dic- tate that any arbitrary number of particles can occupy the same state, it is possible in an extremely low energy environment for particles on the order of Avagadro's number to all condense into the ground state. This state of matter is now called a Bose-Einstein condensate (hereafter referred to as a BEC). This state of matter is interesting because having such a large number of particles in the same state allows for the observation of macroscopic quantum effects.

Priyanka Verma