Quantum Droplet and Bose Polaron

Biswas, Sayak (2021) Quantum Droplet and Bose Polaron. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Sayak Biswas (16MS009)) 16MS009_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

We investigate the fate of weakly interacting, dilute bosonic impurity in dipolar bose gas in quasi one-dimensional geometry. A self-consistent formalism that includes beyond mean �eld corrections systematically is developed and a pair of coupled effective equations that describe the system is derived. In the regime where the bose gas forms a `quantum droplet' the physics of the droplet impurity composite is studied . For repulsive impurity, we observe the formation of quasi-bound states with �nite lifetime which is estimated from shape resonance of asymptotically free impurity particles. We study the collective modes of the droplet impurity composite for the case of an attractive impurity. Below the particle emission threshold, the excitations are bound and correspond to important characteristic modes of the composite. Above the particle emission threshold, we observe the spectacular phenomenon of Feshbach resonance of droplet quasi-particles due to the mixing of bound impurity modes and free particle like excitations of the droplet. The effect of quench of interaction parameters on the impurity is simulated. While the quasi-bound state formed by repulsive impurity diffuses out after the quench, the attractive impurity is found to exhibit stable oscillations. We extend our formalism to the case of mobile impurity in condensate. We propose an effective equation that enables us to study polaronic impurity dynamics in inhomogeneous condensate. iii

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