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Details of Grant 

EPSRC Reference: EP/V03832X/1
Title: Controlled Creation and Dynamics of non-Abelian Vortices and Topological Processes in spinor Bose-Einstein condensates
Principal Investigator: Borgh, Dr MO
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Amherst College
Department: Chemistry
Organisation: University of East Anglia
Scheme: New Investigator Award
Starts: 01 November 2021 Ends: 31 October 2024 Value (£): 378,760
EPSRC Research Topic Classifications:
Quantum Fluids & Solids
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:
Panel DatePanel NameOutcome
21 Apr 2021 EPSRC Physical Sciences 21 and 22 April 2021 Announced
Summary on Grant Application Form
Vortices in fluids are familiar from everyday life, appearing when we stir a cup of tea or drain a bath tub. In superfluids, which flow without viscosity, vortices take on properties arising from the underlying quantum mechanics and behave very differently from what we are used to. Perhaps paradoxically, the consequence is that the fundamental properties of the vortices become relatively insensitive to details of how the particles in the superfluid interact. Instead, the essential features of vortices are understood generically from internal symmetries of the physical state using topology, the field of mathematics that studies what remains unchanged about an object as it is twisted or distorted. Phenomena arising from topology are therefore often universal across seemingly disparate parts of physics and have attracted considerable attention, highlighted by the 2016 Nobel Prize.

Here we will apply theoretical methods to study particular vortices in spinor Bose-Einstein condensates (BECs). This is a superfluid state of matter that appears in certain atomic gases cooled to near absolute zero using techniques that do not freeze out the atoms' quantum-mechanical spin. The spin comes at integer values. We are interested in atoms where the spin is equal to 2, for the reason that the vortices that then appear can be what is called non-Abelian. Vortices are categorised by so-called topological charges. One charge can be added to another, but this addition does not always follow the familiar rules of arithmetics. For non-Abelian vortices, the order matters: A + B is not the same as B + A. This leads to highly counter-intuitive vortex interactions, such that if two vortices collide, they must form a new vortex that continues to connect them even as they move apart. This is not a mere curiosity: analogous objects, described by the same mathematics, can appear also in liquid crystals or in cosmological theories. It is no surprise then that a central goal for experiments is the controlled creation of non-Abelian vortices in the highly accessible spinor BECs, which could act as emulators of physics of much wider importance.

The central task of our project is to provide the theoretical underpinnings for this effort. Several techniques exist for controlled creation of vortices in BECs. However, these cannot be used directly to create vortices that show the non-Abelian properties. We will propose specific protocols for the creation of such vortices and vortex ensembles. We will also, using computer simulations, determine what these vortices look like once they have been allowed to evolve. We can then provide the observable signatures necessary for interpreting the experiments. For this effort to succeed, the work will be done in close contact with experimental project partners at Amherst College, Massachusetts, USA.

We will push the computational limits by simulating dynamical scenarios where topological defects such as vortices determine the physics. For example, the interface between two distinct phases of the same spinor BEC is analogous to similar boundaries in superfluid helium-3. We will determine what vortices are produced when interfaces collide. Importantly, this represents a laboratory scale simulation of processes analogous to those proposed in theories of the early universe. What role do non-Abelian defects play? What can spinor BECs teach us about such processes in general? Defects are also produced when superfluids pass through phase transitions, from one state to another (a familiar example is the freezing of water into ice). Such processes are enormously important also in other quantum systems as well as in cosmology. We will seek to determine whether non-Abelian vortices are produced in the phase transition and, if so, what differences that implies to phase transitions in systems with only Abelian vortices. Again we are motivated by the intriguing prospect of simulating cosmological phenomena in the laboratory.
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