Investigation of quantum measurement and feedback in multipartite quantum systems of ultracold atoms

该项目将利用已经建造的实验设备，在数十纳米开尔文的温度下产生Rb原子的量子气体。牛津大学的研究小组开发的具体实验技术包括将原子限制在由静态磁场和射频磁场组合形成的势中。这使得可以对系统进行高度可控的操作，以产生双势垒势，并将量子气体的维度在三到两个之间改变。Rb原子的特殊性质使它们能够处理内态(在不同超精细能级中)的叠加以及它们在多个势垒中的外部量子态的混合。当这个装置被完全描述后，它独特的能力将被用来研究多体量子系统中的一系列现象。具体目标将是研究在量子反馈方案中产生的这些多体系统的非经典状态，在量子反馈方案中，弱(非破坏性)量子测量的结果被用来控制系统的状态。这样的状态使得精确的测量超越了标准量子极限，然而，本项目的重点将放在量子反馈对这一新机制下集体性质的影响上。对于一个博士学位来说，使用Rb的工作(可能使用不同状态的混合物)将提供足够的结果，但这项工作可以扩展到多种原子物种，如Rb和锶，视进一步的资金而定。与这项工作产生的新可能性相关的理论工作有很大的范围，我们将继续与在这一领域开发新想法的理论家合作。

This project will utilise experimental apparatus that has been constructed to produce quantum gases of rubidium atoms at temperatures of tens of nanokelvin. Specific experimental techniques that have been developed by the research team in Oxford include the confinement of atoms in potentials formed by a combination of static and radiofrequency magnetic fields. These allow highly controllable manipulation of the system to make a double-well potential and also to change the dimensionality of quantum gas between three and two. Special properties of rubidium atoms make them amenable for work with superpositions of internal states (in different hyperfine levels) as well as mixtures of their external quantum states in multiple potential wells. When this apparatus has been fully characterised, its unique capabilities will be used to investigate a wide range of phenomena in many-body quantum systems. Specific goals will be to investigate non-classical states of these multipartite systems arising in quantum feedback schemes in which the results of a weak (non-destructive) quantum measurements are used to control the state of the system. Such states enable precision measurements going beyond the Standard Quantum Limit, however the emphasis in this project will be on the influence of quantum feedback on the collective properties in this new regime. Work with rubidium (with the possibility of using mixtures of different states) will be provide more than sufficient results for a doctorate but this work can be extended to multiple atomic species such as rubidium and strontium, contingent on further funding. There is a large scope for theoretical work associated with the new possibilities arising from this work and we will continue to collaborate with theoreticians who are developing novel ideas in this field.