Originally discovered in liquid helium, superfluidity is an example of quantum mechanics on the macro-scale, where useful bulk behaviour (fluid flow without viscosity) arises from the cooperative behaviour of many tiny particles. This macroscopic quantum behaviour is found in systems as disparate as extremely dense and relatively hot neutron stars, and ultracold dilute-gas Bose-Einstein condensates (BECs), and has direct parallels to another important macroscopic quantum effect – superconductivity (flow of charge without resistance). This research project will explore the role that vortices, quantum whirlpools, play in both supporting and destroying such useful bulk quantum properties. In particular, the successful student will study the interaction between vortices and pinning potentials, of relevance to almost all superfluid and superconducting systems. Free vortices are associated with energy dissipation in both systems, meaning that engineering defects for vortex pinning is a key part of the design of high-temperature superconductors. On the cosmological scale, vortex depinning is expected to be at the heart of the internal dynamics of pulsars and neutron stars, offering an explanation for the peculiar glitches that are observed as the star slows its rotation. Superfluids formed of ultracold atoms provide an extremely clean and well-controlled system for studies of collective quantum behaviour in general, and vortex pinning dynamics in particular. They enable exquisite control over interactions, geometry, and vortex nucleation. Pinning potentials can be created with laser beams and arbitrarily reconfigured, and vortices can be directly imaged with standard optics and a camera. Importantly, in superfluids formed of mixtures of ultracold atoms we can tune the interactions to emphasize quantum effects such as fluctuations.
The successful student will join the Quantum Fluids research team, run by Dr Kali Wilson. They will work closely with the supervisor and other team members on a state-of-the-art experimental apparatus designed to explore vortex dynamics in binary superfluids. The Phd project will focus on (1) the design and implementation of optical systems for controlled vortex nucleation in the superfluid mixture, and (2) a comprehensive study of the interaction between vortices and pinning potentials.
The successful student will also acquire practical skills in the areas of quantum technologies, optics and atomic physics. These skills include working with lasers, designing optical systems, high-resolution imaging and state-of-the-art image processing techniques, cooling and trapping atoms, as well as electronics and mechanical design.