Quantum Transport Experiments with Ultracold Atoms

Abstract

Quantum simulation is a burgeoning field of research, in which quantum systems are engineered to behave similarly to external, complex systems of interest. These quantum simulators are an alternative to the elusive all-purpose ‘quantum computer’ and instead function as analogue computers, allowing an external system of choice to be understood via measurements on a controllable engineered system. An important practical aspect of quantum mechanics concerns its effects on transport. This thesis describes a series of experiments with ultracold atoms in custom optical potentials, detailing quantum simulators developed for analysing the quantum transport properties of specific systems of interest. Two environments in particular are investigated: the quantum chaotic system of the deltakicked rotor, and a spatially disordered potential. The delta-kicked rotor investigations focus on the effects of phase modulation. By applying a periodic phase modulation of f0; 2 =3; 0g, the phase space is modified to generate a Hamiltonian ratchet, manifesting as directed transport within the chaotic sea without any biased force. We characterise the phase space by applying -classical theory, and capitalise on the narrow momentum distribution of a Bose–Einstein condensate by experimentally exploring the phase space. A sinusoidal phase modulation reveals two different transport regimes, dependent on the commensurability of the kicking frequency and phase modulation frequencies. We characterise the resonances found in the commensurate case, and study the effective phase noise induced in the incommensurate case. A particular finding of this investigation is that the quantum resonance is relatively robust to phase noise, while dynamical localisation is inhibited by small levels of phase noise. Finally, we implement a truly custom potential with high resolution imaging of a spatial light modulator, and develop a unique high aspect ratio 2D trap for quantum transport studies over long distances. We create custom spatially disordered channels as part of ‘atomtronic’ circuits to study the effect of disorder in a manner directly analogous to electronic systems. Through measurements of the effective channel resistances, we observe the first signatures of Anderson localisation in a 2D ultracold atom system.