From nonequilibrium phase transitions to topological interfaces in spinor Bose-Einstein condensates

Wheeler, Matthew Thomas (2024) From nonequilibrium phase transitions to topological interfaces in spinor Bose-Einstein condensates. Doctoral thesis, University of East Anglia.

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Spinor Bose-Einstein condensates (BECs) present an experimentally accessible quantum emulator of universal phenomena that appear ubiquitously across physics, some of which are difficult or impossible to study in the laboratory. In this thesis, we investigate a variety of such phenomena in pseudospin-1/2, spin-1, and spin-2 BECs, ranging from quantum phase transitions to topological interfaces. Our investigations start with the relaxation dynamics of quantum turbulence in a two-component BEC containing half-quantum vortices. The temporal scaling of the number of vortices and the correlation lengths are shown to be, at early times, strongly dependent on the relative strength of the interspecies interaction. At later times, the scaling is observed to be universal, independent of the interspecies interaction, and follows scaling laws observed in the relaxation dynamics of scalar BECs, despite our system containing topologically distinct vortices. A spin-1 BEC is then used as an example system for investigating scaling behaviour in a discontinuous (first-order) quantum phase transition. We show how the Kibble-Zurek mechanism can be generalised and applied to our system, which gives associated scaling laws different from those observed in continuous quantum phase transitions. Our predictions are confirmed by mean-field numerical simulations and provide an experimentally accessible system for investigating properties of the decay of metastable states. Spin-2 BECs exhibit multiple ground state phases with continuous or discrete symmetries, making excellent candidates for studying topological interfaces. We analytically construct sets of spinor wave functions that continuously connect two distinct ground state phases, and show how topologically distinct defects and textures can be created that either terminate at the interface or continuously penetrate across it, connecting non-trivially to an object representing a different topology on the other side. Numerical simulations of select examples reveal a range of dynamics, including the formation of composite cores and splitting processes.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Physics
Depositing User: Chris White
Date Deposited: 12 Jun 2024 08:58
Last Modified: 12 Jun 2024 08:58


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