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Abstract
Systems driven far from equilibrium can show radically different properties from the same system at equilibrium. In some cases, new steady-states can emerge, enabling the application of theoretical frameworks typically developed in equilibrium. In this thesis, we discuss the emergence of self-stabilized, square lattice patterns in a Bose-Einstein condensate (BEC) with periodically modulated interactions. We show that despite the dynamical nature of the system, the patterned state displays Goldstone modes that are identical to those of supersolids, which are equilibrium superfluids with spontaneously arising periodic ordering. We first provide a brief overview of the theoretical concepts underpinning the spontaneous emergence of the pattern, as well as its stabilization. We then present the experimental techniques used to observe the pattern, focusing mainly on tunable interactions and local control over the cloud using a digital micromirror device. Experimental results on the emergence of the structure are discussed, demonstrating that the pattern is truly a result of nonlinear phenomena far from equilibrium. We then turn towards explicit imprinting of lattices, which enables us to probe the phonon-phonon interactions that explain pattern stabilization. Beyond imprinting ideal lattices, we also explicitly instigate lattice and superfluid defects, observing their propagation. We identify two distinct speeds of sound for longitudinal excitations and a diffusive mode for transverse lattice deformations. We compare the extracted mode structure to a generic framework of superfluid smectics, extracting relevant hydrodynamic parameters of the system. Finally, we compare the dynamics of wavepackets to collective modes, finding good agreement.
Document type: | Dissertation |
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Supervisor: | Oberthaler, Prof. Dr. Markus |
Place of Publication: | Heidelberg |
Date of thesis defense: | 9 June 2025 |
Date Deposited: | 18 Aug 2025 09:36 |
Date: | 2025 |
Faculties / Institutes: | The Faculty of Physics and Astronomy > Kirchhoff Institute for Physics |