A distinction between hydrodynamic turbulence in a bulk fluid, and in one whose flows are restricted to two dimensions, is that energy dissipation at small length scales is generally inhibited in the latter. Under small-length-scale forcing of energy and vorticity into a two-dimensional (2D) fluid, energy is therefore transferred towards larger scales, opposite that of turbulence in a bulk fluid. Most conspicuously, this means that eddies and vortices may merge to form even larger vortices. Two-dimensional quantum turbulence (2DQT) involves the study of 2D turbulence in quantum fluids such as atomic Bose-Einstein condensates (BECs). In this emerging field of research, numerous open questions generally relate to the dynamics of quantized vortices in superfluids and to the distribution of kinetic energy among length scales. For example, do clusters of quantized vortices of identical circulation naturally emerge in 2DQT flows, as initially predicted by Onsager in 1949? This NSF award supports new experiments aimed at understanding the relationships between vortex distributions, vortex dynamics, and energy spectra in 2DQT. The experimental program of research targeting these topics will utilize highly oblate BECs for the construction of a new imaging system designed to observe vortex dynamics within a BEC, the development of on-demand vortex generation and manipulation methods to study vortex interactions in turbulence with a bottom-up approach, and the study and characterization of developed 2DQT in BECs.
Superfluids such as dilute-gas Bose-Einstein condensates have remarkable properties, including frictionless flow and fluid circulation that is obtained only by the formation of many microscopic quantum whirlpools known as vortices. The distribution and dynamics of these vortices throughout the superfluid provide information on fluid phenomena such as turbulence. This project is studying the generation of quantum vortices and follows their dynamics in pancake-shaped condensates as a means to understand the characteristics of two-dimensional turbulence in superfluids. Turbulence in classical fluids is known to share similarities with quantum turbulence in superfluids, but for the specific case of two-dimensional flows, the similarities and differences between the quantum and classical cases are unclear. This grant supports research and graduate-student mentoring and training involving new methods of creating, manipulating, and detecting quantum vortices in condensates, and probes the characteristics of two-dimensional turbulence in these superfluids. Through controlled studies of two-dimensional quantum turbulence, our aim is to develop new insights on vortex interactions and other phenomena of turbulence, one of the most challenging and complex topics in physics.
