Dipole orientation induced effects in dipolar bose einstein condensates

Abstract

Ultracold quantum gases have thrived as an interdisciplinary field of condensed matter physics quantum optics atomic and molecular physics It boasts set ups with precisely controllable and highly tuneable interaction parameters Research in this area has sparkedafter the realisation of Bose Einstein condensation in alkali atoms in 1995 The goal isto continuously seek quantum gas systems where more and more complex interactions may be embedded Bose Einstein condensation were later achieved in atoms like Cr Er and Dy which have significant dipole moments bringing anisotropic interactions to the quantum gas systems In the last 15 years dipolar Bose Einstein condensates have consistently been found at the forefront of ultracold atomic research Our goal is to explore the tunability of the dipole dipole interaction The simplest way is via an external field which can easily tune the polarisation direction of the dipole moment Effectively it tunes the dipole dipole interaction between the atoms potentiallyfrom repulsive to attractive The effect of this on the collective behaviour of dipolar Bose Einstein condensates are dramatic Below our findings have been outlined for reference We begin by reviewing the advent of the theory of Bose gas and the general short rangetwo body interactions in Chapter 1 We introduce dipolar interactions and prescribe the available methods for tuning these interactions Theoretically these systems are addressed using mean field theory We list the conditions under which mean field theory is applicableand show a glimpse of beyond the mean field theory which becomes crucial in the final chapter In Chapter 2 we review the stability of both homogeneous and trapped Bose Einstein condensates by studying the elementary excitations in the system The theoretical methodologies for calculating Bogoliubov excitations and the low lying modes of the condensates have been explained along with important discoveries from the experimental counterpart The last section in Chapter newline newline