315 research outputs found
A low-loss, broadband antenna for efficient photon collection from a coherent spin in diamond
We report the creation of a low-loss, broadband optical antenna giving highly
directed output from a coherent single spin in the solid-state. The device, the
first solid-state realization of a dielectric antenna, is engineered for
individual nitrogen vacancy (NV) electronic spins in diamond. We demonstrate a
directionality close to 10. The photonic structure preserves the high spin
coherence of single crystal diamond (T2>100us). The single photon count rate
approaches a MHz facilitating efficient spin readout. We thus demonstrate a key
enabling technology for quantum applications such as high-sensitivity
magnetometry and long-distance spin entanglement.Comment: 5 pages, 4 figures and supplementary information (5 pages, 8
figures). Comments welcome. Further information under
http://www.quantum-sensing.physik.unibas.c
Characterization and tomography of a hidden qubit
In circuit-based quantum computing, the available gate set typically consists
of single-qubit gates acting on each individual qubit and at least one
entangling gate between pairs of qubits. In certain physical architectures,
however, some qubits may be 'hidden' and lacking direct addressability through
dedicated control and readout lines, for instance because of limited on-chip
routing capabilities, or because the number of control lines becomes a limiting
factor for many-qubit systems. In this case, no single-qubit operations can be
applied to the hidden qubits and their state cannot be measured directly.
Instead, they may be controlled and read out only via single-qubit operations
on connected 'control' qubits and a suitable set of two-qubit gates. We first
discuss the impact of such restricted control capabilities on the quantum
volume of specific qubit coupling networks. We then experimentally demonstrate
full control and measurement capabilities in a superconducting two-qubit device
with local single-qubit control and iSWAP and controlled-phase two-qubit
interactions enabled by a tunable coupler. We further introduce an iterative
tune-up process required to completely characterize the gate set used for
quantum process tomography and evaluate the resulting gate fidelities
Rarity of figs (Ficus) on Madagascar and its relationship to a depauperate frugivore community
Bien que plusieurs auteurs aient remarquĂ© le faible nombre d'espĂšces frugivores prĂ©sentes Ă Madagascar, l'interprĂ©tation de cette observation n'a jusqu'Ă prĂ©sent fait l'objet que de quelques spĂ©culations. Si l'on compare la forĂȘt
malgache Ă celles des rĂ©gions tropicales de l'Ancien Monde, on y observe que le genre Ficus (gĂ©nĂ©ralement considĂ©rĂ© comme une ressource-clĂ© pour les frugivores des forĂȘts tropicales) prĂ©sente Ă la fois une faible diversitĂ© et une densitĂ© rĂ©duite. La productivitĂ© du groupe des Ficus y est
relativement basse et sa phénologie ne correspond pas aux séquences habituellement observées par ailleurs. Ces facteurs - dont certains pourraient résulter de la longue période au cours de laquelle Madagascar a été isolée des blocs continentaux - sont considérés comme des paramÚtres
importants pour expliquer le nombre réduit des frugivores sur cette ßle
Plant secondary metabolites and primate food choices : a meta-analysis and future directions
The role of plant secondary metabolites (PSMs) in shaping the feeding decisions, habitat suitability, and reproductive success of herbivorous mammals has been a major theme in ecology for decades. Although primatologists were among the first to test these ideas, studies of PSMs in the feeding ecology of non-human primates have lagged in recent years, leading to a recent call for primatologists to reconnect with phytochemists to advance our understanding of the primate nutrition. To further this case, we present a formal meta-analysis of diet choice in response to PSMs based on field studies on wild primates. Our analysis of 155 measurements of primate feeding response to PSMs is drawn from 53 studies across 43 primate species which focussed primarily on the effect of three classes of PSMs tannins, phenolics, and alkaloids. We found a small but significant effect of PSMs on the diet choice of wild primates, which was largely driven by the finding that colobine primates showed a moderate aversion to condensed tannins. Conversely, there was no evidence that PSMs had a significant deterrent effect on food choices of non-colobine primates when all were combined into a single group. Furthermore, within the colobine primates, no other PSMs influenced feeding choices and we found no evidence that foregut anatomy significantly affected food choice with respect to PSMs. We suggest that methodological improvements related to experimental approaches and the adoption of new techniques including metabolomics are needed to advance our understanding of primate diet choice
Predator avoidance and dietary fibre predict diurnality in the cathemeral folivore Hapalemur meridionalis
Though numerous mammalian taxa exhibit cathemerality (i.e. activity distributed across the 24-h cycle), this includes very few primates, exceptions being species from Aotinae and Lemuridae. Four non-mutually exclusive hypotheses have been proposed to explain the ultimate determinants for cathemeral activity in lemurs: thermoregulatory benefits, anti-predator strategy, competition avoidance and metabolic dietary-related needs. However, these have only been explored in the frugivorous genus Eulemur, with some species increasing nocturnality as a possible response to avoid diurnal raptors and to increase their ability to digest fibre during resource-scarce periods. Since Eulemur lack specializations for digesting bulk food, this strategy would allow for processing fibres over the full 24-h. The folivorous lemurids, i.e. genus Hapalemur, provide a divergent model to explore these hypotheses due to gastrointestinal adaptations for digesting dietary fibre and small body size compared to Eulemur. We linked continuous activity data collected from archival tags with observational behaviour and feeding data from three groups of adult Hapalemur meridionalis from January to December 2013. We tested the effects of thermoregulation, predator avoidance and the weighted proportion of digestible dietary fibre on the daily diurnal/nocturnal activity ratio using a Linear Mixed-Model. Our best-fit model revealed that increased canopy exposure and dietary fibre predicted greater diurnality. Our findings partly contrast with previous predictions for frugivorous lemurids. We propose a divergent adaptive explanation for folivorous lemurids. We suggest that the need to avoid terrestrial predators, as well as longer digestive bouts during bulk food periods, may override cathemerality in favour of diurnality in these bamboo lemurs
Ultrasensitive force detection with a nanotube mechanical resonator
Since the advent of atomic force microscopy, mechanical resonators have been
used to study a wide variety of phenomena, such as the dynamics of individual
electron spins, persistent currents in normal metal rings, and the Casimir
force. Key to these experiments is the ability to measure weak forces. Here, we
report on force sensing experiments with a sensitivity of 12 zN Hz^(-1/2) at a
temperature of 1.2 K using a resonator made of a carbon nanotube. An
ultra-sensitive method based on cross-correlated electrical noise measurements,
in combination with parametric downconversion, is used to detect the
low-amplitude vibrations of the nanotube induced by weak forces. The force
sensitivity is quantified by applying a known capacitive force. This detection
method also allows us to measure the Brownian vibrations of the nanotube down
to cryogenic temperatures. Force sensing with nanotube resonators offers new
opportunities for detecting and manipulating individual nuclear spins as well
as for magnetometry measurements.Comment: Early version. To be published in Nature Nanotechnolog
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