RUI: Experiments with Topological Excitations in Bose-Einstein Condensates

Amherst College, Amherst MA

Investigators

Abstract

Modern physics is often an exploration of the extreme environments. For example, the Large Hadron Collider at CERN is a particle accelerator that studies what happens when protons collide at extremely high energy, briefly generating conditions that mimic those of the early universe. At the other end of the energy scale, extremely low-energy collisions (at temperatures only tens of billionths of a degree above absolute zero) contribute to the phenomenon of superfluidity, in which a fluid (such as a very dilute gas) flows without any viscosity. Remarkably, the superfluid gas is itself a pristine "universe," hosting its own "particles" that can be analogues of those existing (or expected to exist) in the cosmos. One example is a particle known as a magnetic monopole, which has not yet been observed but has recently been simulated in a superfluid. Creating such particle-like analogues permits scientists to study some of the properties of anticipated particles in the universe that would otherwise be completely inaccessible, as their creation would exceed the capabilities of even the most powerful particle accelerators. The research in this project is devoted to creation and study of several particle-like structures, including direct analogues of monopoles and more exotic structures known as "knots" and "merons." As simulations, they promise additional insight into the fundamental physical processes of our universe; but they are also of interest in their own right as examples of new and, in many cases, completely unexplored physics. The research program also provides training opportunities for highly motivated undergraduates, a postdoctoral researcher, and a secondary school teacher, with whom we will engage and motivate the next generation of scientists and citizens. Topological structures are central to diverse branches of physics at many different energy and length scales, including cosmology, particle physics, and condensed-matter physics. Superfluids, such as Bose-Einstein condensates, provide new and exciting opportunities to examine these structures in highly-controlled environments. Notably, the complexity of the order parameter describing the superfluid determines what kind of topological excitations it can support. Here, researchers will examine experimentally several aspects of these topological excitations, including quantized vortex dynamics in scalar condensates (total spin F=0) at nonzero temperature, creation of vortex molecules (or "meron pairs") in pseudospinor condensates (effective spin F=1/2), and linked field configurations in quantum fields (or "knots") in spinor condensates (spin F=1). The excitations will be imprinted by exposing the condensate to time-dependent magnetic and optical fields, and will subsequently be analyzed through examination of atomic density profiles using established imaging techniques. Subsequent studies will study their dynamics and interactions, developing new imaging techniques as required.