Fast reprogrammable photonic experiments for quantum foundational studies

我的博士项目将使用实验和理论的混合方法研究量子基础。其目的是进行基础研究，同时考虑量子技术的应用，从而研究这些领域之间的重叠。我将专注于快速可重编程集成光子学用于量子基础实验。我也将做理论工作，其中一些将密切联系到实验，但也有一些独立的理论项目。我将要研究的量子基础领域之一是量子因果关系。在量子力学中，事件之间的因果关系可能具有与量子系统的其他物理性质类似的不确定性，导致不确定的因果顺序[1]。这可能会对我们对时间概念的理解产生重大影响，但它也可以用于量子技术。例如，已经证明了使用量子位门阶的量子叠加的潜在计算优势[2]。量子计量学[3]和通信[4]的可能应用也被研究。具有不确定因果顺序的过程已经在实验中得到了证明[5]，但是为了技术应用，需要创建更复杂过程的叠加。我将从事的第一个项目是我的项目B的直接扩展，这是一个关于高阶量子因果结构的芯片实验，即，比迄今为止的任何实验都要多。我将完成芯片元件的特性，设计PCB，然后进行实验。这可能会占用我的第一年。我们计划的另一个项目是关于反转未知幺正的实验。由幺正操作描述的量子系统的演化原则上是可逆的，但这只有在幺正已知的情况下才有可能。然而，我们往往没有一个完整的描述的物理系统，以确定这个单一的。能够在不需要完全理解系统的情况下逆转幺正操作将有助于研究量子力学中的不可逆性，以及实际应用，例如通过逆转系统的不必要演化来消除噪声。反转酉的协议已经被研究过了，我将研究如何在实验中实现这样的协议。该项目将涉及设计一个芯片，制造它，然后进行实验。最后，我还计划做一个关于量子计算能耗的理论项目。这一领域最近引起了人们的极大兴趣，需要考虑量子计算的潜在负面影响和资源成本[6]。它需要理解量子计算操作的量子热力学，以及这与宏观组件的能量消耗之间的关系。这也可能包括在量子水平上研究能源消耗的可能基本限制。

My PhD project will study quantum foundations using a hybrid approach of both experiment and theory. The aim is to work on foundational studies, whilst considering applications to quantum technologies, thus working on the overlap between these fields. I will focus on fast reprogrammable integrated photonics for use in quantum foundations experiments. I will also do theoretical work, some of which will be closely linked to experimental but also some stand-alone theory projects. One of the areas in quantum foundations that I will be looking at is quantum causality. In quantum mechanics, the causal relations between events can have an uncertainty in a similar way to other physical properties of a quantum system, resulting in an indefinite casual order [1]. This could have a significant impact on our understanding of the notion of time, but it could also be utilised in quantum technology. For example, a potential computational advantage from using a quantum superposition of qubit gate orders has been demonstrated [2]. Possible applications to quantum metrology [3] and communications [4] have also been investigated. Processes with indefinite causal order have been demonstrated experimentally [5], but superpositions of more complex processes will need to be created for technological applications. The first project I will work on is a direct extension of my project B, which is a chip experiment on higher order quantum causal structures, i.e., more parties and more permutations of order than any experimentally achieved so far. I will finish off characterising chip components, design the PCB, and then carry out the experiment. This will likely take up my first year. Another project we have planned is an experiment on reversing unknown unitaries. The evolution of a quantum system described by a unitary operation is in principle reversible, but this is only possible if the unitary is known. However, we often do not have a complete description of a physical system in order to determine this unitary. Being able to reverse a unitary operation without the need to fully understand the system would be useful for studying irreversibility in quantum mechanics, and for practical applications such as removing noise by reversing unwanted evolutions of a system. Protocols for reversing unitaries have been investigated, I will work on how such protocols can be implemented experimentally. The project will involve designing a chip, having it manufactured, and then carrying out the experiment. Finally, I also plan to do a theoretical project on the energy consumption of quantum computing. This area has gained a lot of interest recently, with the need to consider the potential negative impacts and resource costs of quantum computing [6]. It requires understanding the quantum thermodynamics of quantum computation operations, and how this relates to the energy consumption of macroscopic components. This could also include studying possible fundamental limits on energy consumption at the quantum level.