Engineering quantum systems for information processing and metrology using atoms, superconductors, and light

Abstract

This thesis intends to give a concise yet meaningful overview about the progress in the physical realization of quantum information processing using hybrid systems of ultracold atoms and superconducting microwave resonators, describing our own theoretical and experimental contributions to advancing. Ultracold atoms in their ground states are well-isolated quantum systems offering long coherence times, and therefore are prime candidates for quantum memory applications. Their performance is limited by their sensitivity on external magnetic-field noises and inhomogeneous Zeeman shifts inherently present in magnetic traps. We have developed an efficient method to eliminate the magnetic-field dependence of the differential Zeeman shift between the magnetically trappable clock-states up to second order around an arbitrarily chosen offset field, hence rendering atom-based quantum memory insensitive to magnetic noises. We describe two protocols to mediate long-range interactions between Rydberg atoms using a thermally populated microwave cavity, realizing universal 2-bit quantum gates. This is of great practical interest, since in existing hybrid atom-superconducting resonator experiments the attainable temperature is not low enough to reach the vacuum state of the cavity mode. The first method relies on active mode cooling using an auxiliary reservoir of atoms. The second method makes use of a destructive quantum interference between different excitation paths, making the scheme insensitive to the actual photon state of the cavity. We also report on a new laboratory for optical lattice clocks that we have established in parallel with this work. We present a novel concept for continuously operated atomic clocks, along with the steps we have taken towards its experimental realization.