Splitting and recombination of bright-solitary-matter waves

Abstract

This thesis presents the very first experimental realisation of splitting and recombination of robust bright-solitary-matter waves on a narrow repulsive potential barrier. This system has intrinsic interest for fundamental studies of soliton phase and for the realisation of a soliton interferometer.

An upgraded imaging system is presented, which is capable of imaging the bright-solitary-matter waves and across a wide range of magnetic fields. The system uses a combination of an offset-locked imaging laser, a high-intensity probe beam and a microwave-transfer adiabatic rapid passage of the atoms to an auxiliary imaging state which has favourable transition properties.

BECs of Rb are created by direct evaporative cooling, using an upgraded crossed optical dipole trap. Condensates of up to atoms are created, with greater than purity. We develop a wavefunction engineering protocol, which allows us to transfer the condensate into a quasi-1D potential and systematically demonstrate regions of interatomic interactions where bright-solitary-matter waves can be formed, as well as regions where condensate collapse or breathing-mode phenomena are observed. The bright-solitary-matter waves are very robust, propagating without measurable dispersion for over .

The splitting of a soliton into two daughter solitons on a narrow blue-detuned optical potential is presented. We demonstrate full control over the transmission coefficient by varying the barrier height. Velocity selection between the outgoing daughter solitons is observed and quantified, whereby the transmitted daughter soliton always has a higher centre of mass kinetic energy than the reflected daughter soliton.

Velocity-selection-mediated recombination on a wide barrier is demonstrated, as well as interference-mediated recombination on a narrow barrier. We observe large shot-to-shot fluctuations for the narrow barrier which are fully consistent with independently-determined uncertainties in the barrier position. For the first time we explore this experimentally and theoretically, both with Gross-Pitaevskii simulations and analytical approximations, putting new limits on the required parameters for future phase-sensitive interferometric measurements.