Dynamic Properties of Dilute Bose-Einstein Condensates

In this thesis, a new apparatus for the study of Bose-Einstein condensation is described, and the first two experiments performed with the new device are discussed. The new instrument was constructed for the creation of dilute gas sodium Bose-Einstein condensates, and features an optical quality quartz cell, a high-flux spin-flip Zeeman slower, a tightly confining magnetic trap, and a high-resolution imaging system. The theory, design, and construction of each component is discussed, including a detailed explanation of non-destructive dispersive imaging. Bose-Einstein condensation was first achieved in the new apparatus in January of this year. Bose condensates consisting of 10 to 25 million atoms can be produced in this apparatus at a rate of two condensates per minute. The first two experiments performed with the new instrument probed the dynamic properties of dilute Bose condensates, allowing comparisons to be made with long standing theories of weakly-interacting degenerate Bose fluids. The first experiment was the study of “surface wave” excitations of Bose condensates. Standing and rotating quadrupole and octopole excitations were driven with a novel scanned optical dipole potential, a new tool which allows us to generate arbitrary two-dimensional perturbations to the trapping potential which confines the atoms. The second experiment studied the transition from dissipationless to dissipative flow in a Bose condensate. This study, performed by “stirring” the condensate with a focused laser, provided the first experimental evidence for the existence of a critical velocity for dissipation in dilute gas Bose condensates. This experiment is discussed in the context of earlier studies of the critical velocity of superfluid liquid helium. Thesis Supervisor: Wolfgang Ketterle Title: Professor of Physics