Few- and Many-body Physics with Strongly Interacting Bose Gases

This thesis describes experiments that explore few- and many-body physics in strongly interacting Bose gases. Our experimental platform uses Bose-Einstein condensates and cold thermal gases of 39K in different hyperfine states or their combinations, trapped in a quasi-uniform optical potential. We focus on the regime of strong interatomic interactions in the vicinity of scattering (Feshbach) resonances, and our experiments probe both equilibrium physics and post-quench dynamics. The thesis explores three main topics, focusing in turn on two-, three- and many-body physics. In the first set of experiments, we study the two-body physics of single-component gases, where interaction quenches can mix free atoms and two-body bound states (Feshbach dimers), resulting in coherent superposition that can be interferometrically mapped onto oscillations of the apparent atom number. We use such oscillations to map out the dimer binding energy and characterise Feshbach resonances in different hyperfine states. Secondly, we investigate atom loss due to inelastic three-body collisions that mirror the properties of a self-similar series of three-body bound states (Efimov trimers). We map out loss features for attractive and repulsive interactions and different Feshbach resonances in different hyperfine states and show that while the relative positions of such features respect the predicted universal properties, their absolute position deviates from the value theoretically expected for broad Feshbach resonances. Lastly, we explore the many-body physics of highly imbalanced mixtures of two different hyperfine states; atoms in the minority state act as impurities that can become dressed by excitations of the majority bath, realising the Bose polaron scenario. Using spectroscopic and interferometric methods, we probe the response of the system to sudden ‘injection’ of impurities. We investigate the limits of the quasiparticle description for near-resonant interactions and establish the natural scales that universally set the Bose polaron spectrum.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Etrych, Jiri

Advisor dc:contributor.advisor

• Hadzibabic, Zoran

• Bose gases
• Bose polaron
• Efimov physics

Licence

• https://www.repository.cam.ac.uk/bitstreams/ba2212c6-546e-4931-a67d-23ef9ea6610f/download
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.121378

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/389522