NEW RECORDS OF NATIVE AND ALIEN VASCULAR PLANTS FROM ABRUZZO, LAZIO AND MOLISE NATIONAL PARK (ITALY) - AND ADDITIONS TO THE FLORA OF ABRUZZO AND MOLISE ADMINISTRATIVE REGIONS

The Abruzzo, Lazio and Molise National Park, a flagship conservation area in Italy, is a hotspot of floristic diversity and a crossroad for plant biogeography. In this work, as a result of recent field studies in the Park and herbarium revisions, we report 10 taxa new or confirmed for the Abruzzo administrative region, and 3 for the Molise administrative region. Moreover. 47 taxa of vascular plants (41 native and 6 alien taxa) that are new or confirmed for the flora of the Park are reported. Five taxa are excluded from the flora of the Park

Drag in a resonantly driven polariton fluid

We study the linear response of a coherently driven polariton fluid in the pump-only configuration scattering against a point-like defect and evaluate analytically the drag force exerted by the fluid on the defect. When the system is excited near the bottom of the lower polariton dispersion, the sign of the interaction-renormalised pump detuning classifies the collective excitation spectra into three different categories (Ciuti and Carusotto 2005 Phys. Status Solidi b 242 2224): linear for zero, diffusive-like for positive and gapped for negative detuning. We show that both cases of zero and positive detuning share a qualitatively similar crossover of the drag force from the subsonic to the supersonic regime as a function of the fluid velocity, with a critical velocity given by the speed of sound found for the linear regime. In contrast, for gapped spectra, we find that the critical velocity exceeds the speed of sound. In all cases, the residual drag force in the subcritical regime depends on the polariton lifetime only. Also, well below the critical velocity, the drag force varies linearly with the polariton lifetime, in agreement with previous work (Cancellieri et al 2010 Phys. Rev. B 82 224512), where the drag was determined numerically for a finite-size defect

Spin Textures of Polariton Condensates in a Tunable Microcavity with Strong Spin-Orbit Interaction

We report an extended family of spin textures in coexisting modes of zero-dimensional polariton condensates spatially confined in tunable open microcavity structures. The coupling between photon spin and angular momentum, which is enhanced in the open cavity structures, leads to new eigenstates of the polariton condensates carrying quantised spin vortices. Depending on the strength and anisotropy of the cavity confinement potential and the strength of the spin-orbit coupling, which can be tuned via the excitonic/photonic fractions, the condensate emissions exhibit either spin-vortex-like patterns or linear polarization, in good agreement with theoretical modelling

Merging of vortices and antivortices in polariton superfluids

Quantised vortices are remarkable manifestations on a macroscopic scale of the coherent nature of quantum fluids, and the study of their properties is of fundamental importance for the understanding of this peculiar state of matter. Cavity-polaritons, due to their double light-matter nature, offer a unique controllable environment to investigate these properties. In this work we theoretically investigate the possibility to deterministically achieve the annihilation of a vortex with an antivortex through the increase of the polariton density in the region surrounding the vortices. Moreover we demonstrate that by means of this mechanism an array of vortex-antivortex pairs can be completely washed out

Multicomponent polariton superfluidity in the optical parametric oscillator regime

Superfluidity, the ability of a liquid or gas to flow with zero viscosity, is one of the most remarkable implications of collective quantum coherence. In equilibrium systems like liquid 4He and ultracold atomic gases, superfluid behaviour conjugates diverse yet related phenomena, such as persistency of metastable flow in multiply connected geometries and the existence of a critical velocity for frictionless flow when hitting a static defect. The link between these different aspects of superfluid behaviour is far less clear in driven-dissipative systems displaying collective coherence, such as microcavity polaritons, which raises important questions about their concurrency. With a joint theoretical and experimental study, we show that the scenario is particularly rich for polaritons driven in a three-fluid collective coherent regime so-called optical parametric oscillator. On the one hand, the spontaneous macroscopic coherence following the phase locking of the signal and idler fluids has been shown to be responsible for their simultaneous quantized flow metastability. On the other hand, we show here that pump, signal and idler have distinct responses when hitting a static defect; while the signal displays hardly appreciable modulations, the ones appearing in pump and idler are determined by their mutual coupling due to nonlinear and parametric processes