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Abstract Casimir interactions play an important role in the dynamics of nanoscale objects. Here, we investigate the noncontact transfer of angular momentum at the nanoscale through the analysis of the Casimir torque acting on a chain of rotating nanoparticles. We show that this interaction, which arises from the vacuum and thermal fluctuations of the electromagnetic field, enables an efficient transfer of angular momentum between the elements of the chain. Working within the framework of fluctuational electrodynamics, we derive analytical expressions for the Casimir torque acting on each nanoparticle in the chain, which we use to study the synchronization of chains with different geometries and to predict unexpected dynamics, including a “rattleback”-like behavior. Our results provide insights into the Casimir torque and how it can be exploited to achieve efficient noncontact transfer of angular momentum at the nanoscale, and therefore have important implications for the control and manipulation of nanomechanical devices. 

Abstract The large cross sections and strong confinement provided by the plasmon resonances of metallic nanostructures make these systems an ideal platform to implement nanoantennas. Like their macroscopic counterparts, nanoantennas enhance the coupling between deep subwavelength emitters and free radiation, providing, at the same time, an increased directionality. Here, inspired by the recent works in parity-time symmetric plasmonics, we investigate how the combination of conventional plasmonic nanostructures with active materials, which display optical gain when externally pumped, can serve to enhance the performance of metallic nanoantennas. We find that the presence of gain, in addition to mitigating the losses and therefore increasing the power radiated or absorbed by an emitter, introduces a phase difference between the elements of the nanoantenna that makes the optical response of the system directional, even in the absence of geometrical asymmetry. Exploiting these properties, we analyse how a pair of nanoantennas with balanced gain and loss can enhance the far-field interaction between two dipole emitters. The results of this work provide valuable insight into the optical response of nanoantennas made of active and passive plasmonic nanostructures, with potential applications for the design of optical devices capable of actively controlling light at the nanoscale. 

Plasmons, the collective oscillations of mobile electrons in metallic nanostructures, interact strongly with light and produce vivid colors, thus offering a new route to develop color printing technologies with improved durability and material simplicity compared with conventional pigments. Over the last decades, researchers in plasmonics have been devoted to manipulating the characteristics of metallic nanostructures to achieve unique and controlled optical effects. However, before plasmonic nanostructures became a science, they were an art. The invention of the daguerreotype was publicly announced in 1839 and is recognized as the earliest photographic technology that successfully captured an image from a camera, with resolution and clarity that remain impressive even by today’s standards. Here, using a unique combination of daguerreotype artistry and expertise, experimental nanoscale surface analysis, and electromagnetic simulations, we perform a comprehensive analysis of the plasmonic properties of these early photographs, which can be recognized as an example of plasmonic color printing. Despite the large variability in size, morphology, and material composition of the nanostructures on the surface of a daguerreotype, we are able to identify and characterize the general mechanisms that give rise to the optical response of daguerreotypes. Therefore, our results provide valuable knowledge to develop preservation protocols and color printing technologies inspired by past ones.