Our experience of the world around us is governed almost entirely by light–matter interactions. At the most fundamental level, such interactions are described by quantum electrodynamics (QED), a well-established theory that has stood up to decades of experimental testing to remarkable degrees of precision. However, the complexity of real systems almost always means that the quantum electrodynamical equations describing a given scenario are often infeasible or impractical to solve. Thus, a sequence of approximations and idealisations are made, in order to build up from the simple case of an isolated electron interacting with a gauge field leading to the deceptively simple laws governing reflection and refraction at mirrors and lenses. This review provides a pedagogical overview of this journey, concentrating on cases where external boundary conditions can be used as a control method. Beginning from the fundamental Lagrangian, topics include gauge freedom, perturbative macroscopic QED descriptions of spontaneous decay, Casimir–Polder forces, resonant energy transfer, interatomic Coulombic decay, all of which are described in terms of the dyadic Green’s tensor that solves the Helmholtz equation. We discuss in detail how to calculate this tensor in practical situations before outlining new techniques in the design and optimisation of perturbative light–matter interactions, highlighting some recent advances in free-form, unconstrained inverse design of optical devices. Finally, an outlook towards the frontiers in the interaction of quantum light with matter is given, including its interface with chemical reactivity via polaritonic chemistry and quantum chemistry via quantum electrodynamical density functional theory (QEDFT).

我们对周围世界的体验几乎完全由光与物质的相互作用决定。在最基本的层面上，这种相互作用是通过量子电动力学（QED）来描述的，这是一种成熟的理论，经过数十年的实验测试，具有极高的精度。然而，真实系统的复杂性几乎总是意味着描述给定场景的量子电动力学方程通常无法求解或不切实际。因此，进行了一系列近似和理想化，以便从孤立电子与规范场相互作用的简单情况出发，得出控制镜子和透镜反射和折射的看似简单的定律。这篇评论提供了这一旅程的教学概述，重点关注外部边界条件可以用作控制方法的情况。从基本的拉格朗日开始，主题包括规范自由度、自发衰变的微扰宏观 QED 描述、卡西米尔-波尔德力、共振能量转移、原子间库仑衰变，所有这些都用求解亥姆霍兹方程的二进格林张量来描述。我们详细讨论了如何在实际情况下计算这个张量，然后概述微扰光与物质相互作用的设计和优化的新技术，重点介绍光学器件自由形式、无约束逆向设计的一些最新进展。最后，对量子光与物质相互作用的前沿进行了展望，