Thesis

Matter-wave solitons and Floquet-driven instabilities with ultracold atoms in optical lattices

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Awarding institution
  • University of Strathclyde
Date of award
  • 2026
Thesis identifier
  • T18109
Person Identifier (Local)
  • 202283056
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Qualification Name
Department, School or Faculty
Abstract
  • This thesis reports two groups of experiments using ultracold caesium atoms which are trapped in an optical lattice potential. We first demonstrate the existence of matter-wave lattice solitons and characterise their properties. Using an optical accordion lattice with tunable spacing, we prepare atomic wavepackets across a well-defined number of lattice sites. By rapidly changing atomic interactions from repulsive to attractive, the wavepacket is found to remain localised for hundreds of milliseconds. These solitons can be classified as single-site or multisite solitons, which span one or many sites, respectively. We probe the nature of their collapse by observing the wavepacket in time, finding that for strong interactions the local density increases, leading to dynamical collapse and three-body loss. In a second group of experiments, we investigate the role of Floquet heating in periodically driven systems. Floquet engineering has become a key technique to control quantum simulation experiments. By periodically shifting the lattice sites, variables such as the inter-site tunnelling energy can be configured. However, this driving force excites the system and induces heating and instabilities, limiting experimental times. Parametric instabilities occur when the driving frequency matches the energy of an existing phonon mode, while negative-mass instabilities occur whenever the wavepacket enters regions of the Brillouin zone associated with negative effective mass. We probe these instabilities in a range of systems including tilted, untilted, driven, and undriven systems. We measure the fraction of excited atoms for a range of parameters and create stability diagrams, finding stable parameter regimes associated with zero growth.
Advisor / supervisor
  • Kuhr, Stefan
  • Haller, Elmar
Resource Type
DOI

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