Quantum and Many Body Physics Enabled by Advanced Semiconductor Nanotechnology

发光半导体材料和器件主导着日常生活的许多方面。它们的影响力无处不在，提供了使互联网、大面积显示器、房间和街道照明成为可能的来源，仅举几个例子。它们的存在依赖于高质量的半导体结构，这种结构可以通过先进的晶体生长和复杂的纳米加工来制备。我们的提议旨在利用先进的增长和制造，在量子世界实现类似的进步，在量子世界中，通常违反直觉的行为完全受量子力学定律的制约。我们的总体目标是探索在发生根本新型量子光子现象的制度下运行的纳米设备的行为，并有可能支持下一代量子技术。我们专注于两个互补的系统：III-V半导体具有高度完美的晶格，被证明能够逐个发射光子和长相干量子态，以及原子薄的类石墨烯二维(2D)半导体，使其具有新的能带结构、稳定的电子-空穴束缚态(激子)和易于与图案化结构集成。这两种材料系统的结合是一种强大的使能现象，范围从单光子能级到密集的多粒子状态，其中相互作用占主导地位。我们计划的很大一部分集中在芯片上的几何结构上，从而能够根据应用程序的可能需要进行扩展。我们使用的半导体系统与光子相互作用很强；我们将实现通常不相互作用的光子之间的相互作用。我们将进入高度非线性腔量子电动力学的区域。激子(耦合的电子-空穴对)和光子相互作用强烈，使得能级阶梯导致芯片上产生很少的光子态。通过将腔耦合在一起，我们将致力于实现光子的高度关联状态。这些进展很可能成为光子量子处理器和量子通信系统的重要组成部分。在类似的结构中，我们访问高密度的区域，其中电子和空穴凝聚成高度集居态(凝聚态)。我们的目标是回答长期存在的基本问题，即在平衡系统和非平衡系统中可能发生的相变类型，这些系统的损失与收益平衡。我们还将研究最高温度(可能超过100K)的凝聚体系，以及向凝聚态相变的潜在机制。凝聚态系统除了具有根本意义外，还有可能成为新形式的微型相干光源。纳米制造将发挥至关重要的作用，使光能够被限制在亚波长长度尺度上，并制造光子腔，使它们在逃逸之前具有非常长的寿命。在III-V纳米光子结构中放置高质量发射器的能力将得到增强，并有望在世界上领先，这是我们最近委托使用的晶体生长机器，该机器专门为此目的而设计，由英国量子技术计划资助。我们在没有污染的超高真空条件下制备2D异质结构(由两个单独的材料原子组成的薄层)的能力预计也会产生类似的影响，使我们能够实现非常长寿命的束缚电子-空穴对状态，这是凝聚到高密度状态的途径。2D异质结构与图案化光子结构的轻松集成进一步使人们能够研究非线性和量子现象，包括在光流不受缺陷散射影响的拓扑结构中。总的来说，我们已经具备了在基础量子光子学方面取得突破性进展的成分，并具有相当大的潜力来支撑下一代量子技术。

Light emitting semiconductor materials and devices dominate many aspects of everyday life. Their influence is all pervasive providing the sources which enable the internet, large area displays, room and street lighting to give just a few examples. Their existence relies on the high quality semiconductor structures which may be prepared by advanced crystal growth and sophisticated nanofabrication. Our proposal aims to capitalise on the advanced growth and fabrication to achieve similar advances in the quantum world where often counter-intuitive behaviour is governed solely by the laws of quantum mechanics. Our overall aim is to explore the behaviour of nano-devices operating in regimes where fundamentally new types of quantum-photonic phenomena occur, with potential to underpin the next generation of quantum technologies. We focus on two complementary systems: III-V semiconductors with their highly perfect crystal lattices, proven ability to emit photons one by one and long coherence quantum states, and atomically-thin graphene-like two dimensional (2D) semiconductors enabling new band structures, stable electron-hole bound states (excitons) and easy integration with patterned structures. The combination of the two material systems is powerful enabling phenomena ranging from the single photon level up to dense many-particle states where interactions dominate. A significant part of our programme focusses on on-chip geometries, enabling scale-up as likely required for applications. The semiconductor systems we employ interact strongly with photons; we will achieve interactions between photons which normally do not interact. We will gain entry into the regime of highly non-linear cavity quantum electrodynamics. Excitons (coupled electron-hole pairs) and photons interact strongly, enabling ladders of energy levels leading to on-chip production of few photon states. By coupling cavities together, we will aim for highly correlated states of photons. These advances are likely to be important components of photonic quantum processors and quantum communication systems. In similar structures, we access regimes of high density where electrons and holes condense into highly populated states (condensates). We aim to answer long-standing fundamental questions about the types of phase transitions that can occur in equilibrium systems and in out-of-equilibrium ones which have loss balanced by gain. We will also study condensate systems up to high temperatures, potentially in excess of 100K, and of the mechanisms underlying phase transitions to condensed states. The condensed state systems, besides their fundamental interest, also have potential as new forms of miniature coherent light sources.Nanofabrication will play a vital role enabling confinement of light on sub-wavelength length scales and fabrication of cavities for photons such that they have very long lifetimes before escaping. The ability to place high quality emitters within III-V nanophotonic structures will receive enhancement and potential world lead from a crystal growth machine we have recently commissioned, specially designed for this purpose, funded by the UK Quantum Technologies programme. Similar impact is expected from our ability to prepare 2D heterostructures (atomically thin layers of two separate materials placed one on top of the other) under conditions of ultrahigh vacuum free from contamination, enabling realisation of bound electron-hole pair states of very long lifetime, the route to condensation to high density states. The easy integration of 2D heterostructures with patterned photonic structures furthermore enables nonlinear and quantum phenomena to be studied, including in topological structures where light flow is immune to scattering by defects.Taken all together we have the ingredients in place to achieve ground-breaking advances in fundamental quantum photonics with considerable potential to underpin next generations of quantum technologies.