Ultracold atoms in adjustable arrays of optical microtraps

Abstract

Ultracold atoms in optical lattices are a powerful platform for the study of quantum many-body physics. The combination of a high degree of isolation from the environment and external control over all relevant parameters makes these systems ideal candidates for the quantum simulation of fundamental lattice models. However, since the atoms are trapped in standing waves of interfering laser beams, the available trap geometries are constrained to regular lattices and single-site control is limited. In this thesis, an alternative experimental platform is investigated. Here, the combination of a microlens array and a spatial light modulator is used to provide a two-dimensional optical microtrap array for ultracold atoms. This setup allows for versatile trap geometries and comprehensive single-site control. The experimental feasibility of the described platform is investigated in the following way. First, the light field generating the microtrap array is simulated using a detailed model of the optical setup. The computed intensity distribution is proportional to the optical dipole potential for the atoms. Second, the simulation results are used to obtain the Hubbard parameters for multiple alkalies from numerical calculations as well as approximative analytical methods. It is shown that the strongly correlated regimes of the Bose-Hubbard model can be reached at sufficiently large tunneling rates. In addition, the impact of fluctuations in the trap parameters is investigated. Third, two approaches are considered for the preparation of low-entropy many-body states. On the one hand, a loading scheme is investigated which starts from a Bose-Einstein condensate and is used in optical lattice experiments. Here, the depth of the microtrap array is increased adiabatically. On the other hand, an array of isolated traps, which is initialized with one atom per site in the respective motional ground state, is considered as starting point. The itinerant regime of the Hubbard model is accessed by an adiabatic decrease of the trap depth. An analysis of ramp-induced excitations and external heating processes shows the feasibility of both approaches. Demonstrating the potential of the investigated platform, two applications are described. On the one hand, the tunneling dynamics of ultracold atoms between weakly coupled ring lattices is analyzed. Controlled by the interaction strength, multiple phenomena can be observed: Josephson oscillations exhibiting collapse and revival, inter-action-induced self-trapping, and tunneling resonances. On the other hand, the implementation of a scheme for universal quantum computing based on time-continuous quantum walks of interacting particles is proposed. Here, the information is encoded into the position of atomic wave packets moving through a planar graph which is built from optical microtraps and implements a quantum circuit. Details of an experimental implementation are discussed for both applications using the results derived in the preceding parts of this thesis.