No abstract

Active optical elements with ever smaller footprint and lower energy consumption are central to modern photonics. The drive for miniaturisation, speed and efficiency with the concomitant volume reduction of the optically active area has led to the development of devices that harness strong light-matter interactions. By managing the strength of light-matter coupling to exceed losses, quasiparticles, called exciton-polaritons, are formed that combine the properties of the optical fields with the electronic excitations of the active material. Utilising polaritons in inorganic semiconductor microcavities, all-optical transistor functionality was observed albeit at cryogenic temperatures [1]. Here, we replace inorganic semiconductors with a ladder-type polymer in an optical microcavity and realise room temperature operation of a polariton transistor through vibron-mediated stimulated polariton relaxation. We demonstrate net gain of ∼10 dB µm −1 , sub-picosecond switching time, cascaded amplification and all-optical logic operation at ambient conditions.

One of the most attractive commercial applications of semiconductor nanocrystals (NCs) is their use in lasers. Thanks to their high quantum yield, tunable optical properties, photostability, and wet-chemical processability, NCs have arisen as promising gain materials. Most of these applications, however, rely on incorporation of NCs in lasing cavities separately produced using sophisticated fabrication methods and often difficult to manipulate. Here, we present whispering gallery mode lasing in supraparticles (SPs) of self-assembled NCs. The SPs composed of NCs act as both lasing medium and cavity. Moreover, the synthesis of the SPs, based on an in-flow microfluidic device, allows precise control of the dimensions of the SPs, i.e. the size of the cavity, in the micrometer range with polydispersity as low as several percent. The SPs presented here show whispering gallery mode resonances with quality factors up to 320. Whispering gallery mode lasing is evidenced by a clear threshold behavior, coherent emission, and emission lifetime shortening due to the stimulation process.

The recent progress in nanotechnology [1, 2] and single-molecule spectroscopy [3][4][5] paves the way for cost-effective organic quantum optical technologies emergent with a promise to useful devices operating at ambient conditions. We harness a π-conjugated ladder-type polymer strongly coupled to a microcavity forming hybrid light-matter states, so-called exciton-polaritons, to create excitonpolariton condensates with quantum fluid properties. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity undergoing bosonic stimulation [6] which we have managed to trigger at the single-photon level, thereby providing an efficient way for all-optical ultra-fast control over the macroscopic condensate wavefunction. Here, we utilise stable excitons dressed with high energy molecular vibrations allowing for single-photon nonlinearity operation at ambient conditions. This opens new horizons for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental quantum limit.

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity, and aromaticity, with implications for on-surface synthesis, catalysis, photoconversion, and applications in molecular electronics. On insulating, multilayer sodium chloride (NaCl) films, we controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide (CO)-functionalized tips. We detected changes in conformation, adsorption geometry, and bond-order relations for azobenzene, tetracyanoquinodimethane, and pentacene in multiple charge states. Moreover, for porphine, we investigate the charge state-dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemicalstructural changes of individual molecules for a wide range of charge states.