84 research outputs found
Quantum Transport Enhancement by Time-Reversal Symmetry Breaking
Quantum mechanics still provides new unexpected effects when considering the
transport of energy and information. Models of continuous time quantum walks,
which implicitly use time-reversal symmetric Hamiltonians, have been intensely
used to investigate the effectiveness of transport. Here we show how breaking
time-reversal symmetry of the unitary dynamics in this model can enable
directional control, enhancement, and suppression of quantum transport.
Examples ranging from exciton transport to complex networks are presented. This
opens new prospects for more efficient methods to transport energy and
information.Comment: 6+5 page
Environment-assisted quantum transport in a 10-qubit network
The way in which energy is transported through an interacting system governs
fundamental properties in many areas of physics, chemistry, and biology.
Remarkably, environmental noise can enhance the transport, an effect known as
environment-assisted quantum transport (ENAQT). In this paper, we study ENAQT
in a network of coupled spins subject to engineered static disorder and
temporally varying dephasing noise. The interacting spin network is realized in
a chain of trapped atomic ions and energy transport is represented by the
transfer of electronic excitation between ions. With increasing noise strength,
we observe a crossover from coherent dynamics and Anderson localization to
ENAQT and finally a suppression of transport due to the quantum Zeno effect. We
found that in the regime where ENAQT is most effective the transport is mainly
diffusive, displaying coherences only at very short times. Further, we show
that dephasing characterized by non-Markovian noise can maintain coherences
longer than white noise dephasing, with a strong influence of the spectral
structure on the transport effciency. Our approach represents a controlled and
scalable way to investigate quantum transport in many-body networks under
static disorder and dynamic noise.Comment: Mai
Observation of Entangled States of a Fully Controlled 20-Qubit System
We generate and characterise entangled states of a register of 20
individually controlled qubits, where each qubit is encoded into the electronic
state of a trapped atomic ion. Entanglement is generated amongst the qubits
during the out-of-equilibrium dynamics of an Ising-type Hamiltonian, engineered
via laser fields. Since the qubit-qubit interactions decay with distance,
entanglement is generated at early times predominantly between neighbouring
groups of qubits. We characterise entanglement between these groups by
designing and applying witnesses for genuine multipartite entanglement. Our
results show that, during the dynamical evolution, all neighbouring qubit
pairs, triplets, most quadruplets, and some quintuplets simultaneously develop
genuine multipartite entanglement. Witnessing genuine multipartite entanglement
in larger groups of qubits in our system remains an open challenge.Comment: 20 pages, 4 figure
A telecom-wavelength quantum repeater node based on a trapped-ion processor
A quantum repeater node is presented based on trapped ions that act as single
photon emitters, quantum memories and an elementary quantum processor. The
node's ability to establish entanglement across two 25 km-long optical fibers
independently, then to swap that entanglement efficiently to extend it over
both fibers, is demonstrated. The resultant entanglement is established between
telecom-wavelength photons at either end of the 50 km channel. The system
improvements to allow for repeater-node chains to establish stored entanglement
over 800 km at Hertz rates are calculated, revealing a near-term path to
distributed networks of entangled sensors, atomic clocks and quantum
processors.Comment: 5 pages and 4 figures main text plus supplementar
Sr-Nd-Pb-Hf isotope results from ODP Leg 187: Evidence for mantle dynamics of the Australian-Antarctic Discordance and origin of the Indian MORB source
New high precision PIMMS Hf and Pb isotope data for 14–28 Ma basalts recovered during ODP Leg 187 are compared with zero-age dredge samples from the Australian-Antarctic Discordance (AAD). These new data show that combined Nd-Hf isotope systematics can be used as an effective discriminant between Indian and Pacific MORB source mantle domains. In particular, Indian mantle is displaced to lower εNd and higher εHf ratios compared to Pacific mantle. As with Pb isotope plots, there is almost no overlap between the two mantle types in Nd-Hf isotope space. On the basis of our new Nd-Hf isotope data, we demonstrate that Pacific MORB-source mantle was present near the eastern margin of the AAD from as early as 28 Ma, its boundary with Indian MORB-source mantle coinciding with the eastern edge of a basin-wide arcuate depth anomaly that is centered on the AAD. This observation rules out models requiring rapid migration of Pacific MORB mantle into the Indian Ocean basin since separation of Australia from Antarctica. Although temporal variations in isotopic composition can be discerned relative to the fracture zone boundary of the modern AAD at 127°E, the distribution of different compositional groups appears to have remained much the same relative to the position of the residual depth anomaly for the past 30 m.y. Thus significant lateral flow of mantle along the ridge axis toward the interface appears unlikely. Instead, the dynamics that maintain both the residual depth anomaly and the isotopic boundary between Indian and Pacific mantle are due to eastward migration of the Australian and Antarctic plates over a stagnated, but slowly upwelling, slab oriented roughly orthogonal to the ridge axis. Temporal and spatial variations in the compositions of Indian MORB basalts within the AAD can be explained by progressive displacement of shallower Indian MORB-source mantle by deeper mantle having a higher εHf composition ascending ahead of the upwelling slab. Models for the origin of the distinctive composition of the Indian MORB-source based on recycling of a heterogeneous enriched component that consist of ancient altered ocean crust plus<10% pelagic sediment are inconsistent with Nd-Hf isotope systematics. Instead, the data can be explained by a model in which Indian mantle includes a significant proportion of material that was processed in the mantle wedge above a subduction zone and was subsequently mixed back into unprocessed upper mantle
Cancellous bone and theropod dinosaur locomotion. Part I—an examination of cancellous bone architecture in the hindlimb bones of theropods
This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion.
On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling
Dissecting the shared genetic basis of migraine and mental disorders using novel statistical tools
Migraine is three times more prevalent in people with bipolar disorder or depression. The relationship between
schizophrenia and migraine is less certain although glutamatergic and serotonergic neurotransmission are implicated in both. A shared genetic basis to migraine and mental disorders has been suggested but previous studies
have reported weak or non-significant genetic correlations and five shared risk loci. Using the largest samples to
date and novel statistical tools, we aimed to determine the extent to which migraine’s polygenic architecture
overlaps with bipolar disorder, depression and schizophrenia beyond genetic correlation, and to identify shared
genetic loci.
Summary statistics from genome-wide association studies were acquired from large-scale consortia for migraine
(n cases = 59 674; n controls = 316 078), bipolar disorder (n cases = 20 352; n controls = 31 358), depression
(n cases = 170 756; n controls = 328 443) and schizophrenia (n cases = 40 675, n controls = 64 643). We applied the bivariate causal mixture model to estimate the number of disorder-influencing variants shared between migraine
and each mental disorder, and the conditional/conjunctional false discovery rate method to identify shared loci.
Loci were functionally characterized to provide biological insights.
Univariate MiXeR analysis revealed that migraine was substantially less polygenic (2.8 K disorder-influencing variants) compared to mental disorders (8100–12 300 disorder-influencing variants). Bivariate analysis estimated that
800 (SD = 300), 2100 (SD = 100) and 2300 (SD = 300) variants were shared between bipolar disorder, depression and
schizophrenia, respectively. There was also extensive overlap with intelligence (1800, SD = 300) and educational attainment (2100, SD = 300) but not height (1000, SD = 100). We next identified 14 loci jointly associated with migraine
and depression and 36 loci jointly associated with migraine and schizophrenia, with evidence of consistent genetic
effects in independent samples. No loci were associated with migraine and bipolar disorder. Functional annotation
mapped 37 and 298 genes to migraine and each of depression and schizophrenia, respectively, including several
novel putative migraine genes such as L3MBTL2, CACNB2 and SLC9B1. Gene-set analysis identified several putative
gene sets enriched with mapped genes including transmembrane transport in migraine and schizophrenia.
Most migraine-influencing variants were predicted to influence depression and schizophrenia, although a minority
of mental disorder-influencing variants were shared with migraine due to the difference in polygenicity. Similar
overlap with other brain-related phenotypes suggests this represents a pool of ‘pleiotropic’ variants that influence
vulnerability to diverse brain-related disorders and traits. We also identified specific loci shared between migraine and each of depression and schizophrenia, implicating shared molecular mechanisms and highlighting candidate
migraine genes for experimental validation
Symptom-based stratification of patients with primary Sjögren's syndrome: multi-dimensional characterisation of international observational cohorts and reanalyses of randomised clinical trials
Background
Heterogeneity is a major obstacle to developing effective treatments for patients with primary Sjögren's syndrome. We aimed to develop a robust method for stratification, exploiting heterogeneity in patient-reported symptoms, and to relate these differences to pathobiology and therapeutic response.
Methods
We did hierarchical cluster analysis using five common symptoms associated with primary Sjögren's syndrome (pain, fatigue, dryness, anxiety, and depression), followed by multinomial logistic regression to identify subgroups in the UK Primary Sjögren's Syndrome Registry (UKPSSR). We assessed clinical and biological differences between these subgroups, including transcriptional differences in peripheral blood. Patients from two independent validation cohorts in Norway and France were used to confirm patient stratification. Data from two phase 3 clinical trials were similarly stratified to assess the differences between subgroups in treatment response to hydroxychloroquine and rituximab.
Findings
In the UKPSSR cohort (n=608), we identified four subgroups: Low symptom burden (LSB), high symptom burden (HSB), dryness dominant with fatigue (DDF), and pain dominant with fatigue (PDF). Significant differences in peripheral blood lymphocyte counts, anti-SSA and anti-SSB antibody positivity, as well as serum IgG, κ-free light chain, β2-microglobulin, and CXCL13 concentrations were observed between these subgroups, along with differentially expressed transcriptomic modules in peripheral blood. Similar findings were observed in the independent validation cohorts (n=396). Reanalysis of trial data stratifying patients into these subgroups suggested a treatment effect with hydroxychloroquine in the HSB subgroup and with rituximab in the DDF subgroup compared with placebo.
Interpretation
Stratification on the basis of patient-reported symptoms of patients with primary Sjögren's syndrome revealed distinct pathobiological endotypes with distinct responses to immunomodulatory treatments. Our data have important implications for clinical management, trial design, and therapeutic development. Similar stratification approaches might be useful for patients with other chronic immune-mediated diseases.
Funding
UK Medical Research Council, British Sjogren's Syndrome Association, French Ministry of Health, Arthritis Research UK, Foundation for Research in Rheumatology
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