Nonlinear and quantum physics with exciton polaritons
Extreme optical nonlinearities emerge when photons are spatially conﬁned and rendered mutually interacting. Semiconductor optical microcavities are outstanding solid-state systems wherein these two conditions can be simultaneously fulﬁlled. Photons in a microcavity can couple strongly to excitons in semiconductor quantum wells, giving rise to composite light-matter quasi-particles known as polaritons. The excitonic constituent confers polaritons giant interaction strengths, while the photonic constituent enables micron-scale conﬁnement of polaritons followed by photon emission. Hence, polaritons constitute an excellent system for studying light-matter interactions under the influence of tunable interactions, driving, dissipation, and coupling between multiple microcavities. Recently, I have been investigating the interplay of interference and nonlinearity in coupled semiconductor microcavities, and studying non-equilibrium quantum dynamics. The image shows three polariton density profiles observed at the same driving power, i.e. tristability, in a photonic dimer delimited by the dashed lines.
Strong light-matter coupling in metallic nanoparticle arrays
Metallic nanoparticles display remarkable optical effects due to collective oscillations of conduction electrons driven by light, known as localized surface plasmons (LSPs). In a nanoparticle array, LSPs can couple to diffracted waves in the periodicity plane (so-called Rayleigh anomalies), or refractive-index guided modes in a waveguide. These couplings lead to hybrid plasmonic-photonic resonances known as surface lattice resonances (SLRs) and waveguide-plasmon polaritons (WPPs), respectively. A major part of my PhD research focused on the physics and applications of SLRs and WPPs. With SLRs, we studied the tunable properties of bright and dark modes (PRX 2011), observed their collective character (Phys. B 2012), and reported the smallest resonance linewidth for any plasmonic system (ACS Photon. 2014 ). We also explored the weak and strong coupling between SLRs and light emitters, and we demonstrated several novel ways to enhance the light emission spectrum, directionality, and polarization (APL 2012, LSA 2013, PRL 2014). We worked towards creating the first room-temperature polariton condensate in plasmonics (PRL 2013), and recently demonstrated it (Optica 2017). With waveguides we demonstrated the transition from weak to strong waveguide-plasmon coupling (PRB 2014), we observed light-emitting waveguide plasmon polaritons (WPPs) for the first time (PRL 2012), and in combination with liquid crystals demonstrated active control of light emission (Nano Lett. 2014). This research was done in a system (metallic nanoparticles combined with high quantum efficiency emitters) which is relevant for applications to light-emitting devices. In collaboration with Philips we filed for 4 patents, and published an invited review article in Light: Science & Applications discussing challenges and opportunities in the field of metallic nanoparicle arrays for enhanced light emission.