Significance: Space–time-dependent electromagnetic media, whose constitutive parameters are directionally biased in space and time, are a topic of current enormous interest across physics. Here we address a problem of fundamental relevance: the similarities and differences between such modulated materials and the classic problem of moving media. We establish that, surprisingly, the Fresnel drag effect of light in moving media, dictated by special relativity, is also present in modulated media, fully resolving this paradox with an analytical approach. We discuss how nonreciprocity can emerge at vanishing frequency. While we focus on electromagnetism, our findings can be extended to other wave systems.

Time has emerged as a new degree of freedom for metamaterials, promising new pathways in wave control. However, electromagnetism suffers from limitations in the modulation speed of material parameters. Here we argue that these limitations can be circumvented by introducing a traveling-wave modulation, with the same phase velocity of the waves. We show how luminal metamaterials generalize the parametric oscillator concept, realize giant broadband nonreciprocity, achieve efficient one-way amplification, pulse compression, and harmonic generation, and propose a realistic implementation in double-layer graphene.

Here we present the theoretical foundation of the strong coupling phenomenon between quantum emitters and propagating surface plasmons observed in two-dimensional metal surfaces. For that purpose, we develop a quantum framework that accounts for the coherent coupling between emitters and surface plasmons and incorporates the presence of dissipation and dephasing. Our formalism is able to reveal the key physical mechanisms that explain the reported phenomenology and also determine the physical parameters that optimize the strong coupling. A discussion regarding the classical or quantum nature of this phenomenon is also presented.

We study a one-dimensional plasmonic system with non-trivial topology: a chain of metallic nanoparticles with alternating spacing, which in the limit of small particles is the plasmonic analogue to the Su-Schrieffer-Heeger model. Unlike prior studies we take into account long range hopping with retardation and radiative damping, which is necessary for the scales commonly used in plasmonics experiments. This leads to a non-Hermitian Hamiltonian with frequency dependence which is notably not a perturbation of the quasistatic model. We show that the resulting band structures are significantly different, but that topological features such as quantised Zak phase and protected edge modes persist because the system has the same eigenmodes as a chirally symmetric system. We discover the existence of retardation-induced topological phase transitions, which are not predicted in the SSH model. We find parameters which lead to protected edge modes and confirm that they are highly robust under disorder, opening up the possibility of protected hotspots at topological interfaces which could have novel applications in nanophotonics.

Topological photonic systems, with their ability to host states protected against disorder and perturbation, allow us to do with photons what topological insulators do with electrons. Topological photonics can refer to electronic systems coupled with light or purely photonic setups. By shrinking these systems to the nanoscale, we can harness the enhanced sensitivity observed in nanoscale structures and combine this with the protection of the topological photonic states, allowing us to design photonic local density of states and to push towards one of the ultimate goals of modern science: the precise control of photons at the nanoscale. This is paramount for both nanotechnological applications and fundamental research in light matter problems. For purely photonic systems, we work with bosonic rather than fermionic states, so the implementation of topology in these systems requires new paradigms. Trying to face these challenges has helped in the creation of the exciting new field of topological nanophotonics, with far-reaching applications. In this article, we review milestones in topological photonics and discuss how they can be built upon at the nanoscale.