Observation of spontaneous density-wave patterns using a quantum gas magnifier

Abstract

This thesis reports the implementation of a matter wave optics protocol for the magnification of quantum gases. The protocol consists of a quarter period evolution in a harmonic trap followed by a free expansion. Subsequently, we image the magnified density distribution via standard absorption imaging. We reach a magnification of more than 90, allowing for sub-lattice site resolved imaging of the atomic density in an optical lattice with a lattice constant of 709 nm. The technique overcomes several limitations of established methods as it has very large depth of focus, does not induce light assisted collisions, and records the density in a single shot. We benchmark the method by high precision thermometry of the normal to superfluid transition and demonstrate its capabilities by achieving pattern preparation using magnetic resonance techniques, by presenting measurements of sub-lattice site dynamics, and by an analysis of thermal and quantum fluctuations of on-site populations. In a next step we leverage the advantages of the quantum gas magnifier to observe spontaneous pattern formation in a Bose-Einstein condensate in a tilted triangular lattice with weak transverse confinement, i.e., in a three-dimensional system. To the best of our knowledge, this phenomenon was not observed or predicted beforehand and explicitly requires the capabilities of matter wave magnification to be visible. We explain the observation by a theoretical modelling in terms of an effective Hamiltonian for large tilts and in terms of a c-field numerical simulation.