Dartmouth Events

Abstract: Remarkable advances have been made in the past decade in the ability to control superfluids in circuit-like configurations. Especially notable are the improvements in the initialization, stabilization and measurement of the circulation of superfluids in geometries with periodic boundary conditions, such as rings. This has significant implications for applications as rotation sensors, magnetometers, and in the emerging field of atomtronics. As the push towards studying supercurrents in lower dimensions and higher aspect ratios continues, in order to realize idealized experimental conditions and explore unusual quantum phases, phase fluctuations become increasingly pronounced, with the potential to destroy long-range order. In this thesis, I report my work on reliably initializing persistent current states in fermionic superfluids, and the impact of phase fluctuations as we push towards lower dimensions.

We first initialize persistent current states in a narrow superfluid ring, by stirring with a repulsive barrier. We report unprecedented reliability at initializing current states of higher orders using stirring techniques. The flow properties of these current states are intimately tied to the presence of vortices confined to the interior of the rings. We have found evidence of successfully pinning these confined vortices at a designated location. A novel interferometric phase extraction algorithm is also introduced, which enables the automation of measuring the winding number of the rings, and a window into studying the stability of phase around the ring.

We further investigate the role of thermal phase fluctuations in narrow coplanar, concentric rings of ultracold fermionic superfluids. We found that the correlation length decreases with number density, consistent with theoretical expectations. We also observed that increasing the coupling between the rings leads to greater overall coherence in the system. The phase fluctuations increased with a change from periodic to closed boundary conditions as we applied a potential barrier at one point in a ring. These results are relevant for the implementation of proposals to utilize ultracold quantum gases in large and elongated circuit-like geometries, especially those that require deterministic preparation and control of quantized circulation states. The work represents an important milestone and a necessary prelude to experiments involving quasi-1D quantum rings.

 

PhD Thesis Advisor: Professor Kevin Wright