Coherent control of the silicon-vacancy spin in diamond

Spin impurities in diamond have emerged as a promising building block in a wide range of solid-state-based quantum technologies. The negatively charged silicon-vacancy centre combines the advantages of its high-quality photonic properties with a ground-state electronic spin, which can be read out optically. However, for this spin to be operational as a quantum bit, full quantum control is essential. Here we report the measurement of optically detected magnetic resonance and the demonstration of coherent control of a single silicon-vacancy centre spin with a microwave field. Using Ramsey interferometry, we directly measure a spin coherence time, T2*, of 115±9 ns at 3.6 K. The temperature dependence of coherence times indicates that dephasing and decay of the spin arise from single-phonon-mediated excitation between orbital branches of the ground state. Our results enable the silicon-vacancy centre spin to become a controllable resource to establish spin-photon quantum interfaces.We acknowledge financial support by the University of Cambridge, the ERC Grant PHOENICS, FP7 Marie Curie Initial Training Networks S3NANO and SPIN NANO, and the NQIT programme. This research has been partially funded by the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant agreement no. 611143 (DIADEMS). B.P. thanks Wolfson College (Cambridge) for support through a Research Fellowship

Survey of Leafhopper Species in Almond Orchards Infected with Almond Witches'-Broom Phytoplasma in Lebanon

Leafhoppers (Hemiptera: Auchenorrhyncha: Cicadellidae) account for more than 80% of all “Auchenorrhynchous” vectors that transmit phytoplasmas. The leafhopper populations in two almond witches'-broom phytoplasma (AlmWB) infected sites: Tanboureet (south of Lebanon) and Bourj El Yahoudieh (north of Lebanon) were surveyed using yellow sticky traps. The survey revealed that the most abundant species was Asymmetrasca decedens, which represented 82.4% of all the leafhoppers sampled. Potential phytoplasma vectors in members of the subfamilies Aphrodinae, Deltocephalinae, and Megophthalminae were present in very low numbers including: Aphrodes makarovi, Cicadulina bipunctella, Euscelidius mundus, Fieberiella macchiae, Allygus theryi, Circulifer haematoceps, Neoaliturus transversalis, and Megophthalmus scabripennis. Allygus theryi (Horváth) (Deltocephalinae) was reported for the first time in Lebanon. Nested PCR analysis and sequencing showed that Asymmetrasca decedens, Empoasca decipiens, Fieberiella macchiae, Euscelidius mundus, Thamnottetix seclusis, Balclutha sp., Lylatina inexpectata, Allygus sp., and Annoplotettix danutae were nine potential carriers of AlmWB phytoplasma. Although the detection of phytoplasmas in an insect does not prove a definite vector relationship, the technique is useful in narrowing the search for potential vectors. The importance of this information for management of AlmWB is discussed

Psyllid Vectors

BGPI : équipe 6International audience‘Candidatus Phytoplasma’ species are mostly transmitted from plant to plant by phloem feeding hemipterans, primarily leafhoppers (Cicadellidae) and planthoppers (Fulgoroidea) (Hemiptera, Auchenorrhyncha). However, there is one group of phytoplasmas, the 16SrX or apple proliferation group, whose members are transmitted by psyllid vectors of the superfamily Psylloidea (Hemiptera, Sternorrhyncha). These psyllid-transmitted phytoplasmas are genetically closely related and are associated with economically important diseases of fruit trees such as pear decline, apple proliferation and European stone fruit yellows. The psyllid vector species of these phytoplasmas are also closely related and all belong to the genus Cacopsylla. Both, phytoplasmas and psyllid vectors, are geographically limited to the Palaearctic region, mainly Europe. Only pear decline and peach yellow leaf roll phytoplasmas have probably been introduced to America along with their vectors. As phytoplasma-infected trees cannot be cured and resistant plant material is not available to the growers, preventive control measures such as vector control are of paramount importance to limit the spread of these diseases. Thus, detailed knowledge about the biology and ecology of the vector species, their host plants as well as knowledge about the transmission parameters is crucial

The Family Acholeplasmataceae (Including Phytoplasmas)The Prokaryotes

The family Acholeplasmataceae was originally established to accommodate the genus Acholeplasma, comprising the mollicutes that could be cultivated without the supplement of cholesterol and that use UGA as a stop codon instead of coding for tryptophan. It was later shown that the phytoplasmas, a large group of uncultivable, wall-less, non-helical mollicutes that are associated with plants and insects, shared taxonomically relevant properties with members of the genus Acholeplasma. Being not cultivable in vitro in axenic culture, the phytoplasmas could not be classified using the standards used for other mollicutes and are named using the category of Candidatus, as “Ca. Phytoplasma.” Although phytoplasmas are associated with habitats and ecology different from acholeplasmas, the two genera Acholeplasma and “Candidatus Phytoplasma” are phylogenetically related and form a distinct clade within the Mollicutes. The persisting inability to grow the phytoplasmas in vitro hinders the identification of their distinctive phenotypic traits, important criteria for mollicute classification. Until supplemental phenotypic traits become available, the genus “Candidatus Phytoplasma” is designated, on the basis of phylogeny, as a tentative member in the family Acholeplasmataceae. Phylogenetic analysis based on gene sequences, in particular, ribosomal sequences, has provided the major supporting evidence for the composition and taxonomic subdivision of this group of organisms with diverse habitats and ecology and has become the mainstream for the Acholeplasmataceae systematics. However, without the ability to determine phenotypic properties, the circumscription of related species among the non culturable members of the family remains a major issue. The genus Acholeplasma comprises 14 species predominantly associated with animals and isolated from mammalian fluids but regarded as not normally pathogenic. Conversely, the genus “Ca. Phytoplasma” includes plant pathogens of major economic relevance worldwide. To date, 36 “Ca. Phytoplasma species” have been described