Quantum nonlinear optics with 2D materials

当火炬发出的两束光束交叉时，它们不会像《星球大战》中的军刀那样相互碰撞，而只是继续各自的道路。这是从自由光子不相互作用的事实得出的。然而，当放置在适当的介质中时，光子可以有效地感觉到彼此的存在，使得光学系统的响应依赖于光子的数量。在这种情况下，我们说它具有介质提供的光学非线性。通常体积越大，非线性越强，目标是在尽可能小的尺度上实现突出的非线性。与“军刀效应”一起，非线性最终可以为光子提供有效的量子态操纵。从而制备出具有高度非线性的单光子态，并将其应用于量子信息处理。这将导致超高速量子计算和通信平台，作为量子应用的基础，包括安全通信网络，提高计算能力和传感水平，没有量子技术就无法达到。当光被限制在一个光学腔内（例如，由两个镜子设置），它与介质的相互作用大大增强。如果光子往返的平均次数变大，它们就会与介质中的激发相杂化，从而产生半光半物质的准粒子——极化子。杂化使受限光和产生的极化子能够相互作用。这种能力在经典非线性光学的许多应用中取得了进展，包括用于快速宽带通信的光孤子。然而，寻找一个最优系统的任务仍然是一个悬而未决的问题，其中极化的大非线性是在少数量子的限制下实现的。在这个项目中，我将发现如何在极小的尺度上增加光学非线性。这将通过研究二维（2D）材料中的强光-物质耦合而成为可能，其中单层厚度可以小于一纳米。考虑到几层的组合，我将展示极化的非线性响应可以提升到单光子过程可以观察到的水平。因此，这项研究将使这些易于生产的量子光学处理微型系统成为可负担得起的量子技术的平台。

When two beams from light torches cross, they do not clash like sabres from "Star Wars", but simply continue each its own way. This follows from the fact that free photons do not interact. However, when placed in an appropriate medium, photons can effectively feel the presence of each other, making the response of the optical system dependent on the number of photons. In this case, we say it has an optical nonlinearity provided by the medium. Typically the larger the volume, the stronger the nonlinearity, and the goal is to achieve prominent nonlinearity at the smallest possible scale. Together with the "sabre-effect", nonlinearity can ultimately provide the efficient manipulation of quantum states for photons. Thus with high level of nonlinearity single photon states can be prepared and used in quantum information processing. This would result in ultrafast quantum computing and communication platforms, serving as the basis for quantum applications that include secure communication networks, increased computational power and sensing at a level impossible to reach without quantum technologies.When light is confined in an optical cavity (for instance, set by two mirrors), its interaction with the medium is greatly enhanced. If the average number of roundtrips made by photons becomes large, they can hybridize with excitations in the medium, leading to half-light half-matter quasiparticles - polaritons. The hybridization makes confined light and the resulting polaritons able to interact. This ability stays behind the progress in numerous applications of classical nonlinear optics, including optical solitons for fast broadband communication. However, the task of finding an optimal system, where large nonlinearity for polaritons is achieved in the limit of few quanta, remains an open question.In the project, I will discover ways to increase optical nonlinearity at the minuscule scale. This will become possible by studying strong light-matter coupling in two-dimensional (2D) materials, where monolayer thickness can be smaller than a nanometer. Considering combinations of a few layers, I will show that the nonlinear response for polaritons can be elevated to the level where single photon processes become observable. The research will thus enable these easy-to-produce miniature systems for quantum optical processing to function as a platform for affordable quantum technologies.