Size-dependent nonlocal effects in plasmonic semiconductor particles

Localized surface plasmons (LSP) in semiconductor particles are expected to exhibit spatial nonlocal response effects as the geometry enters the nanometer scale. To investigate these nonlocal effects, we apply the hydrodynamic model to nanospheres of two different semiconductor materials: intrinsic InSb and $n$-doped GaAs. Our results show that the semiconductors indeed display nonlocal effects, and that these effects are even more pronounced than in metals. In a $150\mathrm{\,nm}$ InSb particle at $300\mathrm{\,K}$, the LSP frequency is blueshifted 35%, which is orders of magnitude larger than the blueshift in a metal particle of the same size. This property, together with their tunability, makes semiconductors a promising platform for experiments in nonlocal effects.Comment: 7 pages, 3 figures, 1 table, corrected typos in text and figure

Quantum optical effective-medium theory for loss-compensated metamaterials

A central aim in metamaterial research is to engineer sub-wavelength unit cells that give rise to desired effective-medium properties and parameters, such as a negative refractive index. Ideally one can disregard the details of the unit cell and employ the effective description instead. A popular strategy to compensate for the inevitable losses in metallic components of metamaterials is to add optical gain material. Here we study the quantum optics of such loss-compensated metamaterials at frequencies for which effective parameters can be unambiguously determined. We demonstrate that the usual effective parameters are insufficient to describe the propagation of quantum states of light. Furthermore, we propose a quantum-optical effective-medium theory instead and show that it correctly predicts the properties of the light emerging from loss-compensated metamaterials.Comment: 6 pages, 3 figures. Accepted for Physical Review Letter

Coupling Nitrogen Vacancy Centers in Diamond to Superconducting Flux Qubits

We propose a method to achieve coherent coupling between Nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light.Comment: Accepted in Phys. Rev. Lett. Updated text and Supplementary Material adde

Inter-and intraspecific variation in fern mating systems after long-distance colonization: the importance of selfing

<p>Abstract</p> <p>Background</p> <p>Previous studies on the reproductive biology of ferns showed that mating strategies vary among species, and that polyploid species often show higher capacity for self-fertilization than diploid species. However, the amount of intraspecific variation in mating strategy and selfing capacity has only been assessed for a few species. Yet, such variation may have important consequences during colonization, as the establishment of any selfing genotypes may be favoured after long-distance dispersal (an idea known as Baker's law).</p> <p>Results</p> <p>We examined intra-and interspecific variation in potential for self-fertilization among four rare fern species, of which two were diploids and two were tetraploids: <it>Asplenium scolopendrium </it>(2n), <it>Asplenium trichomanes </it>subsp. <it>quadrivalens </it>(4n), <it>Polystichum setiferum </it>(2n) and <it>Polystichum aculeatum </it>(4n). Sporophyte production was tested at different levels of inbreeding, by culturing gametophytes in isolation, as well as in paired cultures with a genetically different gametophyte. We tested gametophytes derived from various genetically different sporophytes from populations in a recently planted forest colonized through long-distance dispersal (Kuinderbos, the Netherlands), as well as from older, less disjunct populations.</p> <p>Sporophyte production in isolation was high for Kuinderbos genotypes of all four species. Selfing capacity did not differ significantly between diploids and polyploids, nor between species in general. Rather selfing capacity differed between genotypes within species. Intraspecific variation in mating system was found in all four species. In two species one genotype from the Kuinderbos showed enhanced sporophyte production in paired cultures. For the other species, including a renowned out crosser, selfing capacity was consistently high.</p> <p>Conclusions</p> <p>Our results for four different species suggest that intraspecific variation in mating system may be common, at least among temperate calcicole ferns, and that genotypes with high selfing capacity may be present among polyploid as well as diploid ferns. The surprisingly high selfing capacity of all genotypes obtained from the Kuinderbos populations might be due to the isolated position of these populations. These populations may have established through single-spore colonization, which is only possible for genotypes capable of self-fertilization. Our results therewith support the idea that selection for selfing genotypes may occur during long-distance colonization, even in normally outcrossing, diploid ferns.</p

A multiple-scattering approach to interatomic interactions and superradiance in inhomogeneous dielectrics

The dynamics of a collection of resonant atoms embedded inside an inhomogeneous nondispersive and lossless dielectric is described with a dipole Hamiltonian that is based on a canonical quantization theory. The dielectric is described macroscopically by a position-dependent dielectric function and the atoms as microscopic harmonic oscillators. We identify and discuss the role of several types of Green tensors that describe the spatio-temporal propagation of field operators. After integrating out the atomic degrees of freedom, a multiple-scattering formalism emerges in which an exact Lippmann-Schwinger equation for the electric field operator plays a central role. The equation describes atoms as point sources and point scatterers for light. First, single-atom properties are calculated such as position-dependent spontaneous-emission rates as well as differential cross sections for elastic scattering and for resonance fluorescence. Secondly, multi-atom processes are studied. It is shown that the medium modifies both the resonant and the static parts of the dipole-dipole interactions. These interatomic interactions may cause the atoms to scatter and emit light cooperatively. Unlike in free space, differences in position-dependent emission rates and radiative line shifts influence cooperative decay in the dielectric. As a generic example, it is shown that near a partially reflecting plane there is a sharp transition from two-atom superradiance to single-atom emission as the atomic positions are varied.Comment: 18 pages, 4 figures, to appear in Physical Review

Topsoil translocation in extensively managed arable field margins promotes plant species richness and threatened arable plant species

peer reviewedSince the 1950s, agriculture has intensified drastically, which has led to a significant biodiversity decline on arable lands. This decline was especially dramatic for segetal plant species, the specialist species of cereal fields. Due to the low population density and poor dispersal abilities of many segetal species, the recovery of species-rich fields may fail even though the environmental conditions are suitable. Therefore, conservation efforts including active restoration measures aimed at recovering segetal vegetation are needed. To this purpose, we propose to alleviate dispersal limitation by means of topsoil translocation from a species-rich donor arable field. At two receiver sites, we tested this technique using two topsoil-spreading densities, i.e. 2.5Lsoil/m2 and 5Lsoil/m2 in experimental plots (3 m2). At one receiver site, we tested the impact of topsoil translocation from two different donor sites, while in the other receiver site one donor site was used. We compared plant species diversity and composition of treated plots with control plots as well as with the species composition of the donor sites (field survey) and their seed bank (greenhouse survey). Species richness was increased by topsoil spreading, including richness of threatened species. 33% and 71% of the threatened species were successfully translocated respectively at the two receiver sites. At one site, plant cover was also increased, including threatened species cover. Conversely, topsoil spreading did not promote pernicious species that could affect farmer acceptance negatively. Vegetation of translocated plots was more similar in terms of species composition to donor site seed banks than to donor site field survey. The higher spreading density led to increased species richness when seed bank in topsoil had lower density. Our results show that topsoil translocation can be a highly effective method for restoring threatened segetal plant communities in agricultural landscapes. Even when a full plant community was already present (Receiver 1) topsoil transfer led to a doubling in species richness. The seed bank surveys were a good indicator of plant community composition upon topsoil translocation in the field and are therefore advisable to implement in the project-planning phase to evaluate donor site potential. From our results, we recommend to spread soil at an overall rate of 500 seeds/m2 equivalent. Future studies need to assess the long-term fate of the translocated species as well as the impacts of soil harvests on the donor sites to establish sustainable use levels. © 2020 Elsevier Lt