Investigating quantumness in complex systems under adverse conditions

为了正常工作，跑车的引擎需要它的所有部件一起工作，遵循一个精确的模式。这意味着，复杂的机械部件和电路必须以一致的方式进行设计。赛车的性能将关键取决于这个乐团的组合方式。然而，为了提高发动机的效率(并在故障时进行维修)，我们希望能够访问和控制每一个小轮子、保险丝和活塞。任何有车(并且喜欢自己动手进行机械维护和维修)的人都知道，这通常意味着有必要把手放进车里，试图接触到发动机的特定部件，并检查其状态和效率。这是对我的项目中涉及的主题和情况的外行隐喻，该项目将在贝尔法斯特女王大学开发，研究和分析由多方组成的复杂量子系统，所有这些系统都相互作用，在困难的工作条件下运行。为了提高基于使用这种复杂系统的量子协议的性能，我建议遵循通过正确理解这种系统的行为方式所经过的道路。我将寻找适当的相互作用配置，能够优化多体系统中的量子分布，并允许将外部世界的影响降至最低。事实上，后者通常对任何量子行为都是有害的。为了实现这一切，我将开发适当的分析工具，就目前已使用的方法而言是新颖的，特别是设计成接近实验实际的。这些形式的工具将扩展到数值领域，用于评估更复杂的情况。我将考虑参与复杂系统动力学的特定组件难以寻址的情况，以及单个对象的量子行为不易揭示的情况。后一种情况的发生可能是因为系统的内在属性，这些属性将它推向经典演化，决定了它的量子态的脆弱性。这项研究的目的是设计策略，基于具有更可操纵的辅助状态的适当耦合的工程设计，允许间接揭示此类有问题的情况的动力学中的非经典特征。这两项任务都是极其及时和重要的，因为它们接近了当前理论和实验工作的核心两点。它们的目标是将在量子水平上操作的控制扩展到更大的强关联粒子系统，以及在更现实和技术要求较低的条件下操作的介观对象。该项目的成功将提供有效的、实际可执行的协议，用于将量子化实施到复杂的设备中，并对其进行推断，以对抗由于与无处不在的外部世界的不可控相互作用而产生的古典性。这两个目标对于更好地理解量子到经典的转变，以及发现是否有可能将量子进化的前沿推向一个通常被认为仅仅是经典的领域，都是至关重要的。

In order to work properly, the engine of a sports car needs all its parts to work together, following a precise pattern. This means that a complicated ensemble of mechanical parts and electric circuitry has to be engineered in a consistent way. The performances of the car will critically depend on the way this ensemble has been put together. However, in order to improve the efficiency of the engine (and also to repair it when it breaks down), we would like to have access and control over every single small wheel, fuse and piston. Anyone having a car (and enjoying a bit of do-it-yourself mechanical maintenance and repair) knows that this often implies the necessity of put the hands into it , trying to reach exactly a specific component of the engine and check its status and efficiency.This serves us a layman metaphor for the topics and situations addressed in my project, to be developed at Queen's University Belfast, where intricate quantum systems made out of many parties, all mutually interacting and operating under difficult working conditions, are considered and analysed. In order to improve the performances of quantum protocols based on the use of such complex systems, I propose to follow the path that passes through a proper understanding of the way such systems behave. I will look for appropriate configurations of interactions able to optimise the distribution of quantumness within a many-body system and allowing for the minimisation of the influences of the outside world. In fact, these latter are usually detrimental to any quantum behaviour. In order to achieve this all, I will develop proper analytical tools, novel with respect to the approaches that have been used soi far, specifically designed so as to be close to experimental reality. These formal tools will be extended to the numerical domain for the assessment of even more complicated situations.I will consider the case of difficult addressability of specific components participating to the dynamics of a complex system, as well as the situation of a single object whose quantum behaviour cannot be easily revealed. This latter situation can occur because of the system's intrinsic properties, which push it towards classical evolutions, determining the frailty of its quantum state. The aim of this investigation is the design of strategies, based on the engineering of proper couplings with more manipulable auxiliary states, which allow the indirect revelation of nonclassical features in the dynamics of such problematic cases. Both these tasks are extremely timely and important as they approach two points which are at the core of current theoretical and experimental efforts. They are directed towards the extension of control operated at the quantum level to larger systems of strongly correlated particles and to mesoscopic objects operating under more realistic and less technically demanding conditions. The success of the project will provide effective, practically implementable protocols for the enforcement of quantumness into complex devices and its inference, made possible against the classicality induced by uncontrollable interactions with the ubiquitous outer world . Both these targets are pivotal to gather a better understanding of the quantum-to-classical transition and to discover whether it is possible to push the frontiers of quantum evolutions to a realm that is commonly thought to be merely classical.