Cavity based ion entanglement via fibre optic connections.

量子比特之间的量子纠缠(例如体现在原子、离子、光子或超导电路中)是量子信息处理所需的基本资源之一。然而，纠缠的产生往往效率低下，并且使用了大量的光学组件，限制了量子计算和通信方案的可扩展性。在这个项目中，我们的目标是通过光纤耦合的光学谐振器来克服这些限制。特别是，我们专注于使用捕获的超冷离子来存储量子信息的系统。将离子放置在高精细度的腔内会导致离子和单光子之间的强烈光学耦合，然后可以通过光纤连接进行传输和交换。这样的方案将允许更有效的纠缠产生，从而减少纠错所需的冗余量子比特的数量，更好的可扩展性，以及更具成本效益的量子器件。对于量子通信来说，近确定性纠缠的关键是使用脉冲整形技术(如受控发射)来增加第二个腔的重新吸收。这个项目将研究单光子脉冲形状如何影响通过单模光纤传输~100米-~10公里尺度距离后的重新吸收。对于量子计算来说，有效纠缠的关键是平衡腔-离子系统的耦合、反射镜的反射率以及系统的总体损耗。对于一个有效的系统，这些参数应该被优化，以提供最大的成功纠缠的机会。这个项目的目标是研究囚禁离子系统的这两个使用案例，以确定这些系统的最佳参数和实验限制。

Quantum entanglement between qubits (embodied for example in atoms, ions, photons, or superconducting circuits) is one of the essential resources required for quantum information processing. However, entanglement generation is often inefficient and utilises a large range of optical components, limiting the scalability of quantum computation and communication schemes. In this project we aim to overcome these limitations with the help of optical resonators coupled via optical fibres. In particular, we focus on systems that employ trapped ultracold ions to store quantum information. Placing the ions inside high finesse cavities leads to strong optical coupling between the ions and single photons, which can then be transmitted and exchanged via the optical fibre connections. Such schemes will allow for more efficient entanglement generation, thus reducing the number of redundant qubits required for error correction, better scalability, and more cost effective quantum devices.For quantum communications the key to near deterministic entanglement is the use of pulse shaping techniques (such as controlled emission) to increase re-absorption by the second cavity. This project will look at how the single photon pulse shape affects this re-absorption after travelling ~100m - ~10km scale distances through a single mode fibre.For quantum computation the key to efficient entanglement is to balance the coupling of a cavity - ion system, the reflectivity of the mirrors, and the overall losses in the system. For an efficient system these parameters should be optimised to give the maximum chance of success for entanglement. The goal of this project is to look at both of these use cases for trapped ion systems to determine optimal parameters and the experimental limits of these systems.