NSF-BSF: Rotating Ultracold Fermi Gases in a Box

Yale University, New Haven CT

Investigators

Abstract

The behavior of fluids in rotating containers has long been a crucial topic in both fundamental and applied hydrodynamics, including in the study of turbulence. When everyday – classical - fluids are slowly set in rotation, they display a well-known progressive rotation motion. The response to rotation of quantum fluids is strikingly different. Below a certain rotation frequency, these fluids do not respond to the rotation of their container; if they are rotated sufficiently fast, swirling eddies called vortices appear. Those vortices have distinctly quantum properties, and are key to understanding the hydrodynamics of quantum fluids. In particular, the turbulence of quantum fluids is dominated by the interactions between vortices, and by the interactions between excitations of vortices and sound waves. One of the main motivations in studying turbulence in quantum fluids is that, because of the discrete well-defined nature of quantum vortices, it is more fundamental than the more common turbulence of classical fluids and could provide a blueprint for the understanding of the latter. This project will tackle this topic by using gases of ultracold atoms as quantum fluids. These gases will be trapped using boxes made of light, carved using programmable electro-optic devices. Exploiting these devices’ fast real-time characteristics, the ultracold gases will be set in rotation and the nucleation of quantized vortices and the excitations of these vortices will be studied. The ability to project nearly arbitrary “movies” on quantum matter will herald a new stage in quantum control and provide an additional step towards programmable quantum simulation. This project will support the training of two graduate students to modern techniques in atomic physics and the versatile control of quantum matter with light. Uniform quantum gases have recently proven to be an exciting new class of quantum fluids, with distinct advantages. This project will combine these novel uniform gases and real-time control of the atom traps to study aspects of superfluidity in textbook settings. This project will use optical-box trapped gases to study the onset of superfluidity in strongly interacting quantum fluids and the collective excitations of vortex filaments. Despite extensive experimental and theoretical efforts, several fundamental issues about superfluidity remain outstanding. One such equilibrium problem is the relation between superfluid density, the order parameter and the condensed fraction in a strongly interacting superfluid. A second, out of equilibrium, example is the problem of the forces acting on a vortex. Those forces have crucial consequences on the mutual friction between the superfluid and normal components of quantum fluids and on the mass of a vortex. The calculation of such forces is notably controversial. This project will investigate both the regime of sub-critical and supercritical rotation. Off-equilibrium three-dimensional single-vortex states will be produced and used to investigate problems of the inertial mass of a vortex and the nature of various collective excitations of vortex filaments. Numerical simulations of the Gross-Pitaveskii and the Bogoliubov-de Gennes equations will guide the experiments by testing rotation protocols in optical boxes as well as mechanisms to excite and probe the collective excitations of the vortices. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.