Exploring quantum enhancements from indefinite causality and time-reversing gates

从无限因果关系和时间反转门探索量子增强

• 批准号: 2745052
• 金额: --
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2745052
• 关键词: Exploring; quantum; enhancements; indefinite; causality

The notion that events happen in defined causal orders, where one event temporally follows another, is innate to our understanding of the classical world we live in. However, the laws of quantum mechanics allow the strict assumption of a definite causal order to be relaxed, giving rise to events with indefinite causal orders arising from quantum superpositions of causally ordered processes [1]. Indefinite causality can be exploited to achieve advantages in quantum computation [2], quantum communication [3,4], quantum metrology [5], and other information processing tasks [6]. It also has implications for the foundations of quantum theory and concepts in quantum gravity. The aim of this project is to investigate the fundamental concepts underlying indefinite causality and explore potential new quantum advantages that can be harnessed, both on theoretical and experimental fronts. In this hybrid project, I will first work on (i) the theoretical aspect of formulating physical processes able to violate so called "causal inequalities" [7] (bounds on the correlations between events which hold whenever these take place in a well-defined causal order), and (ii) theoretical advantages that can be achieved from indefinite causality, before moving onto experimental work using integrated photonics. On the experimental side, I will perform experiments to illustrate the advantage of indefinite causality in quantum metrology, using a silicon photonic chip that has already been fabricated and is now ready for characterisation. Based on the results obtained in the first (theoretical) phase of this project, this project may also include first prototype experiments demonstrating the violation of causal inequalities, or indefinite causal order processes involving 4 parties. Alongside the work on indefinite causality, I will also study a conceptually related concept, namely, the possibility of temporally reversing unknown unitary operations [8,9] and its applications for quantum technologies. I will extend the theoretical work I started in Project A for a protocol to perform quantum key distribution (QKD) noiselessly along a channel that applies unitary noise. I will also design an on-chip experiment to demonstrate the protocols in Ref. [8,9].

事件以特定的因果顺序发生，其中一个事件在时间上跟随另一个事件，这一概念与生俱来，是我们对我们所生活的古典世界的理解。然而，量子力学定律允许放松对确定因果顺序的严格假设，产生由因果顺序过程的量子叠加引起的不确定因果顺序的事件[1]。无限因果关系可以被用来在量子计算[2]、量子通信[3，4]、量子计量学[5]和其他信息处理任务[6]中获得优势。它还对量子理论的基础和量子引力的概念产生了影响。这个项目的目的是研究无限因果关系背后的基本概念，并探索可以在理论和实验方面利用的潜在新量子优势。在这个混合项目中，我将首先研究(I)能够违反所谓的“因果不等”的物理过程的理论方面[7](当这些事件以明确的因果顺序发生时，事件之间的相关性的界限)，以及(Ii)在使用集成光子学进行实验工作之前，可以从不确定的因果关系中获得的理论优势。在实验方面，我将使用已经制造并准备进行表征的硅光子芯片来进行实验，以说明量子计量学中无限因果关系的优势。基于本项目第一(理论)阶段所获得的结果，本项目还可能包括演示违反因果不平等或涉及四方的不确定因果顺序过程的第一个原型实验。除了不确定因果关系的工作外，我还将研究一个概念上的相关概念，即时间上逆转未知么正操作的可能性[8，9]及其在量子技术中的应用。我将扩展我在项目A中开始的关于协议的理论工作，该协议沿着施加么正噪声的通道无声地执行量子密钥分发(QKD)。我还将设计一个片上实验来演示参考文献中的协议。[8，9]。