Abstract
Plasmons, the electromagnetic excitations coupled with electron waves, possess the intrinsic ability of manipulating light at subwavelength scales down to picometer. This ability not only helps uncovering the fascinating quantum behaviors that strengthen the basic understanding of quantum science, but also enables the inventions of various quantum optoelectronic devices, triggering the birth of quantum plasmonic technology. The past decade has witnessed the flourishing of this technology. In this review, we first focus on fundamental investigations into quantum behaviors for both "isolated" plasmonic nanostructures and "coupled" plasmon-emitter systems, emphasizing new theoretical frameworks and experimental advances. Leveraging on these fundamentals, the progress in exploring and applying quantum plasmonic devices is discussed, such as quantum plasmonic circuits, nanolasers, biochemistry, and spin-orbit interaction devices. Upon summarizing the past and present developments, the future research directions and promising applications are highlighted.