Controlling Rings of Trapped Ions for Quantum Information Applications

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Quantum computing promises to speed up computations by exploiting the unique properties of quantum physics that dictates that quantum systems can be in multiple states at the same time. This non-classical property, called "superposition", can be used to design new computer algorithms that process information faster, as, for example, in the factorization of large numbers on which many modern encryption schemes rely. The difficulty is that superposition states are so fragile that even small amounts of noise, for example from electric fields, can remove the quantum advantage. The goal of this project is to establish a novel ring configuration of trapped ions for quantum computing. To date quantum computational schemes that employ trapped ions as the logical bits have relied on a linear string of ions. This new ring architecture will reduce the influence of the dominant noise source, thereby increasing the accuracy of the quantum operations. In addition to quantum computation benefits, the ring shape also opens up opportunities to study aspects of the fundamental physics behind quantum mechanics, the theory that currently best describes the atomic world. Specifically, because the ion ring can freely rotate, it allows for the study of effects present in large rotating objects and symmetric systems. Thus, the project will explore unique avenues towards quantum information processing and provide novel insights into quantum mechanics as well as offering students new possibilities in this rapidly-developing field of technology.A symmetric ring of ions offers the opportunity to study a number of phenomena requiring translationally symmetric systems and ring topologies as well as to implement quantum gates that benefit specifically from the ring geometry. However, in order to realize any of these studies, a high degree of control over the quantum state of the ions and their collective motion is necessary. For this, the ring must not only be symmetric but also well cooled and have the rotational degree of freedom precisely controlled. Towards these goals, ions will be trapped with oscillating electric fields above a planar electrode configuration. The electrode configuration is carefully chosen to trap the ions in a compact ring far away from symmetry breaking imperfections of the substrate. To establish the degree of symmetry of the ring, cooling to temperatures in the low microkelvin range will be required. Hence, emphasis will be given to various cooling techniques including ground state cooling in an asymmetric configuration followed by adiabatic transformation into a symmetric ring. Of particular interest for quantum information applications is the rate with which the rotational (quantum) state changes. After this characterization phase, laser light will be used to initiate controlled rotation depending on the quantum information stored in individual ions. This interaction will be used to implement the key operation for any meaningful quantum computing, namely quantum operations of an individual (qu)bit conditioned on the state of another bit.