Non-classicality: Quantum entanglement and beyond. Novel concepts and applications

量子力学预测了无法从经典力学的角度理解的物理效应。从根本上讲，我们对物理系统的这种“量子”感兴趣，是为了测试和更好地理解量子力学本身。从实践的角度来看，任何量子效应都可能构成真正颠覆性技术的基础。特别是，量子信息处理领域的发展是认识到信息是物理的(R.Landauer)的结果，并结合了自然界的基本定律是量子的事实。量子信息处理的应用范围从量子计算机相对于经典计算机可能的指数加速-例如，在解决计算问题和有效地模拟量子系统--到安全的加密通信方案。要想利用量子行为，需要对它有最好的理解。该项目旨在描述和利用单粒子和多粒子系统的量子特性和行为。量子纠缠--即两个(或多个)量子系统之间比经典更强的关联--已被证明是许多量子信息处理任务中的关键资源，被认为是最突出的量子特征。另一方面，纠缠以外的关联的非经典性质直到最近才被普遍忽视，但这可能会导致更实用的方法来利用“量子力量”。该项目将解决以下问题：“量子世界中的关联与经典世界中的关联有何不同？”；“我们如何量化、操纵和利用量子？”；“纠缠总是有用的资源吗？”；“有没有简单的测试来检查实验设备在量子体制下工作？”；“是什么让量子计算机潜在地比经典计算机更强大？”在给出这些问题的答案时，我们将采用统一的观点，即非经典是量子系统的一个非常普遍的特征，这远远超出了纠缠。后者将被作为一种极端的非古典主义形式来研究，它允许出现原本不可能实现的效果。

Quantum Mechanics predicts physical effects that cannot be understood from the point of view of Classical Mechanics. From a fundamental point of view, we are interested in this "quantumness" of physical systems in order to test and better understand Quantum Mechanics itself. From a practical point of view, any quantum effect may form the basis for truly disruptive technologies. In particular, the development of the field of Quantum Information Processing is the result of the recognition that "Information is physical" (R. Landauer), combined with the fact that the basic laws of nature are quantum. Applications of Quantum Information Processing range from a possible exponential speed-up of quantum computers over classical computers---e.g., in solving computational problems and efficiently simulating quantum systems---to secure cryptographic communication schemes. Taking advantage of quantum behavior requires the best possible understanding of it. The project aims at characterizing and exploiting the quantum properties and behaviour of single and multipartite systems. Quantum entanglement---i.e., stronger-than-classical correlations between two (or more) quantum systems---has been proved to be a key resource in many Quantum Information Processing tasks and is considered the most prominent quantum feature. On the other hand, non-classical properties of correlations other than entanglement have been generally overlooked until recently, but could lead to more practical ways to harness the "quantum power". The project will address the questions: "how do correlations in the quantum world differ from correlations in the classical world?"; "how can we quantify, manipulate and take advantage of quantumness?"; "is entanglement always a useful resource?"; "are there simple tests to check that experimental devices work in a quantum regime?"; "what makes quantum computers potentially more powerful than classical computers?". In providing an answer to these questions we will adopt the unifying point of view that non-classicality is a very general feature of quantum systems, which goes well beyond entanglement. The latter will be studied as an extreme form of non-classicality that allows otherwise impossible effects.