Tailoring optical metamaterials to tune the atom-surface Casimir-Polder interaction

Metamaterials are fascinating tools that can structure not only surface plasmons and electromagnetic waves but also electromagnetic vacuum fluctuations. The possibility of shaping the quantum vacuum is a powerful concept that ultimately allows engineering the interaction between macroscopic surfaces and quantum emitters such as atoms, molecules or quantum dots. The long-range atom-surface interaction, known as Casimir-Polder interaction, is of fundamental importance in quantum electrodynamics but also attracts a significant interest for platforms that interface atoms with nanophotonic devices. Here we perform a spectroscopic selective reflection measurement of the Casimir-Polder interaction between a Cs(6P_{3/2}) atom and a nanostructured metallic planar metamaterial. We show that by engineering the near-field plasmonic resonances of the metamaterial, we can successfully tune the Casimir-Polder interaction, demonstrating both a strong enhancement and reduction with respect to its non-resonant value. We also show an enhancement of the atomic spontaneous emission rate due to its coupling with the evanescent modes of the nanostructure. Probing excited state atoms next to nontrivial tailored surfaces is a rigorous test of quantum electrodynamics. Engineering Casimir-Polder interactions represents a significant step towards atom trapping in the extreme near field, possibly without the use of external fields.Comment: 21 pages, 9 figure

Coupling of atomic quadrupole transitions with resonant surface plasmons

We report on the coupling of an electric quadrupole transition in atom with plasmonic excitation in a nanostructured metallic metamaterial. The quadrupole transition at 685 nm in the gas of Cesium atoms is optically pumped, while the induced ground state population depletion is probed with light tuned on the strong electric dipole transition at 852 nm. We use selective reflection to resolve the Doppler-free hyperfine structure of Cesium atoms. We observed a strong modification of the reflection spectra at the presence of metamaterial and discuss the role of the spatial variation of the surface plasmon polariton on the quadrupole coupling.Comment: 6 pages, 5 figure

Metamaterial enhancement of metal-halide perovskite luminescence

Metal-halide perovskites are rapidly emerging as solution-processable optical materials for light emitting applications. Here we adopt a plasmonic metamaterial approach to enhance photoluminescence emission and extraction of methylammonium lead iodide (MAPbI3) thin films, based on the Purcell effect. We show that hybridization of the active metal-halide film with resonant nanoscale sized slits carved into a gold film can yield more than one order of magnitude enhancement of luminescence intensity, and nearly threefold reduction of luminescence lifetime. This shows the effectiveness of resonant nanostructures in controlling metal-halide perovskite light emission properties over a tunable spectral range, a viable approach toward highly efficient perovskite light emitting devices and single-photon emitters

Plasmono-Atomic Interactions on a Fiber Tip

Light-atom interaction can be engineered by interfacing atoms with various specially designed media and optical fibers are convenient platforms for realization of compact interfaces. Here, we show that an optical fiber sensor bearing a plasmonic metasurface at its tip can be used to detect modifications of the Doppler-free hyperfine atomic spectra induced by coupling between atomic and plasmonic excitations. We observed the inversion of the phase modulation reflectivity spectra of Cesium vapor in presence of the metamaterial. This work paves the way for future compact hybrid atomic devices with a cleaved tip as substrate platform to host various two-dimensional materials.Comment: 12 pages, 3 figure

Perovskite quantum dot topological laser

Various topological laser concepts have recently enabled the demonstration of robust light-emitting devices that are immune to structural deformations and tolerant to fabrication imperfections. Current realizations of photonic cavities with topological boundaries are often limited by outcoupling issues or poor directionality and require complex design and fabrication that hinder operation at small wavelengths. Here we propose a topological cavity design based on interface states between two one-dimensional photonic crystals with distinct Zak phases and demonstrate a lithography-free, single-mode perovskite laser emitting in the green. Few monolayers of solution processed all-inorganic cesium lead halide perovskite quantum dots are used as ultrathin gain medium. The topological laser has planar design with large output aperture, akin to vertical-cavity surface-emitting lasers (VCSELs) and is robust against variations of the thickness of the gain medium, from deeply subwavelength to thick quantum dot films. This experimental observation also unveils the topological nature of VCSELs, that is usually overlooked in the description of conventional Fabry-Perot cavity lasers. The design simplicity and topological characteristics make this perovskite quantum dot laser architecture suitable for low-cost and fabrication tolerant vertical emitting lasers operating across the visible spectral region

Retrieving positions of closely packed sub-wavelength nanoparticles from their diffraction patterns

Distinguishing two objects or point sources located closer than the Rayleigh distance is impossible in conventional microscopy. Understandably, the task becomes increasingly harder with a growing number of particles placed in close proximity. It has been recently demonstrated that subwavelength nanoparticles in closely packed clusters can be counted by AI-enabled analysis of the diffraction patterns of coherent light scattered by the cluster. Here we show that deep learning analysis can determine the actual position of the nanoparticle in the cluster of subwavelength particles from a sing-shot diffraction pattern even if they are separated by distances below the Rayleigh resolution limit of a conventional microscope.Comment: 6 pages, 3 figure

Modular sito-specific grassing as an agroecological strategy in viticultural systems

Currently, agriculture is strongly dependent on the availability of fossil fuels, other external inputs and natural resources contributing about one fifth to the global emission of greenhouse gases into the atmosphere. There are, however, ample opportunities to mitigate the impact of agricultural activities on the climate. By appropriate soil management, organic and biodynamic woody systems can become quantitatively important sites for the provision of ecosystem services (protection of water, soil, biodiversity and landscape, carbon sequestration and efficient use of water resources), able to actively counteract climate change. The agroecological system developed proposed by the "AgroEcology Participatory Research Group\u201d (University of Bologna), introduce, among the innovative and highly sustainable techniques of soil management, the "stripped" biodiverse grassing, already successfully adopted in Italy and abroad. The system consists in the cultivation, along the row, of legumes and grasses with low water requirements, some of which are self-reseeding (eg. subterranean clover, burclover) and of a mixture of herbaceous species (eg. French honeysuckle, field beans, barley) in the alley. Noteworthy, the inclusion of these species, particularly of self-reseeding legumes, does not imply additional water consumption during the summer period. The soil protection provided by herbaceous species after cutting (or rolling) in the alleys and by self-reseeding legumes in the row, reduce soil evaporation and organic matter oxidation phenomena. Field trials conducted in different Italian farms have demonstrated the multiple benefits of the modular sito-specific grassing enhancing carbon sequestration, biodiversity, resilience and productivity of the viticultural systems