Site-Controlled Single-Photon Emitters Fabricated by Near-Field Illumination.

Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site-controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N-2H and N-2H-H complexes, which neutralize all the effects of N on GaAs, including the N-induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the NH bonds located within the light spot generated by a scanning near-field optical microscope tip are broken, thus obtaining site-controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single-photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.

Generalized Fano lineshapes reveal exceptional points in photonic molecules.

The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices.

Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna.

Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the "campanile tip", a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.