Phase Transitions in driven 1D and Quasi-Periodic 2D Optical Lattices

Ultracold atoms in optical lattices are a versatile experimental platform. They facilitate precisely controlled quantum simulations of a broad range of condensed matter phenomena. This thesis will describe work undertaken with this platform, to explore phase transitions in two different systems. The first is the observation of a first-order Mott transition in a resonantly shaken lattice. The second, is the realisation of a two dimensional Bose glass state in an optical quasicrystal. Quasicrystalline patterns posses long-range order but lack periodicity. This places them in the spectrum of materials between clean, ordered crystals and disordered, amorphous solids. They share properties of both disordered structures and ordered materials, resulting in a rich variety of physical phenomena. This thesis focuses on a novel ground state phase exhibited by our eightfold symmetric optical quasicrystal: the Bose glass. This is a localised phase resulting from the interplay of disorder, in the form of aperiodicity, and interactions. In this regard, I will detail two experiments. The first experiment measures the ground state phase diagram of the quasicrystal as a function of both the lattice depth and interaction strength. The 2D optical quasicrystal is found to support both a superfluid (extended) phase and a Bose glass (localised) phase. The Bose glass phase occurs for lattice depths above a critical point, which gets shifted to larger depths as interactions are increased. This measurement constitutes the first realisation of a 2D Bose glass phase. The second experiment explores the quench dynamics of this phase transition. Rapidly crossing the BG/SF phase boundary induces transient out-of-equilibrium dynamics that depend on properties of the underlying Hamiltonian. This establishes quantum quenches as means to uncover the relaxation dynamics in the long and short term following a rapid change in parameter. The other investigations involve Floquet physics; the study of time periodic Hamiltonians. Introducing periodic time dependence circumvents many challenges of performing quantum simulations with ultracold atoms. Periodic driving introduces a different set of parameters, allowing one to simulate many phenomena that would otherwise be inaccessible. This thesis will present our use of sinusoidal shaking to perform band engineering in a quasi-1D lattice. I will detail our experimental observation of a discontinuous version of the Mott insulator to superfluid transition. This is the first quantum simulation of a discontinuous quantum phase transition in a strongly correlated system. These investigations will open the door to further studies in a 2D square lattice, and eventually the full quasicrystal.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Bhave, Shaurya

Advisor dc:contributor.advisor

• Schneider, Ulrich

• Atomic Physics
• Many Body Quantum Dynamics
• Optical Lattices
• Phase Transitions
• Quasicrystals
• Ultracold Atoms

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/ab98d698-a0ba-4798-aa57-cd2aa26bfd14/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.99955

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/353941