Controlling Rings of Trapped Ions for Quantum Information Applications

量子计算有望通过利用量子物理的独特特性来加快计算速度，量子物理特性决定了量子系统可以同时处于多种状态。这种被称为“叠加”的非经典性质可以用于设计新的计算机算法，以更快地处理信息，例如，在许多现代加密方案所依赖的大数的因数分解中。困难在于叠加态非常脆弱，即使是很小的噪音，比如电场的噪音，也能消除量子优势。该项目的目标是为量子计算建立一种新的被困离子环构型。迄今为止，使用捕获离子作为逻辑位的量子计算方案依赖于离子的线性串。这种新的环形结构将减少主要噪声源的影响，从而提高量子运算的精度。除了量子计算的好处之外，环的形状也为研究量子力学背后的基础物理学提供了机会，量子力学是目前描述原子世界最好的理论。具体来说，因为离子环可以自由旋转，它允许研究存在于大型旋转物体和对称系统中的效应。因此，该项目将探索量子信息处理的独特途径，为量子力学提供新的见解，并为学生在这个快速发展的技术领域提供新的可能性。一个对称的离子环提供了机会来研究许多需要平移对称系统和环拓扑的现象，以及实现量子门，特别是从环几何结构中受益。然而，为了实现这些研究中的任何一项，对离子的量子态及其集体运动的高度控制是必要的。为此，环不仅要对称，而且要有良好的冷却和旋转自由度的精确控制。为了达到这些目标，离子将被平面电极结构上方的振荡电场捕获。电极的结构是精心选择的，以捕获离子在一个紧凑的环远离基板的对称破坏缺陷。为了建立环的对称程度，将需要冷却到低微开尔文范围内的温度。因此，重点将放在各种冷却技术，包括基态冷却在一个不对称的配置，然后绝热转化为对称环。对于量子信息应用，特别感兴趣的是转动（量子）态变化的速率。在这个表征阶段之后，激光将根据存储在单个离子中的量子信息来启动受控旋转。这种相互作用将用于实现任何有意义的量子计算的关键操作，即单个（qu）比特的量子操作取决于另一个比特的状态。

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.