Interfacing ultracold atoms with nanomagnetic domain walls

Abstract

This thesis presents the first realisation of a new type of hybrid quantum device based on spintronic technology. We demonstrate an interaction between the magnetic fringing fields produced by domain walls within planar permalloy nanowires and a cloud of ultracold Rubidium 87 atoms. This interaction is manifested through the realisation of a magnetic atom mirror produced by a two-dimensional domain wall array. The interaction is tuned through the reconfiguration of the micromagnetic structure.

Analytic modelling of the fringing fields is developed and shows good agreement with calculations based on micromagnetically simulated structures. The accurate and rapid calculation of the fringing fields permits simulation of the resulting atom dynamics, which agrees well with data. In turn, we use the atom dynamics as a probe of the micromagnetic reconfiguration processes that take place and observe a collective behaviour which is both reliably reproducible and in agreement with alternative, conventional magnetometry. We also observe evidence of stochastic behaviour, characteristic of superparamagnetic systems.

We consider the development of a more advanced spintronics-based atom chip which will allow for the creation of extremely tight mobile atom traps. We consider the problems associated with ensuring that the trapping potential is adiabatic, sufficiently deep, and technically feasible. In particular we examine techniques to circumvent losses due to Majorana spin-flip transitions. As a result of this study we propose a novel scheme for creating time-averaged potentials via the piezoelectric actuation of magnetic field sources. We show that this technique presents significant fundamental and technical advantages over conventional time-averaging schemes.