65 research outputs found
Crossed Andreev reflection and elastic co-tunneling in a three-site Kitaev chain nanowire device
The formation of a topological superconducting phase in a quantum-dot-based
Kitaev chain requires nearest neighbor crossed Andreev reflection and elastic
co-tunneling. Here we report on a hybrid InSb nanowire in a three-site Kitaev
chain geometry - the smallest system with well-defined bulk and edge - where
two superconductor-semiconductor hybrids separate three quantum dots. We
demonstrate pairwise crossed Andreev reflection and elastic co-tunneling
between both pairs of neighboring dots and show sequential tunneling processes
involving all three quantum dots. These results are the next step towards the
realization of topological superconductivity in long Kitaev chain devices with
many coupled quantum dots
Driving performance and neurocognitive skills of long-term users of sedating antidepressants
Objective: To assess driving performance and neurocognitive skills of long‐term users of sedating antidepressants, in comparison to healthy controls. Methods: Thirty‐eight long‐term (>6 months) users of amitriptyline (n = 13) and mirtazapine (n = 25) were compared to 65 healthy controls. Driving performance was assessed using a 1‐h standardised highway driving test in actual traffic, with road‐tracking error (standard deviation of lateral position [SDLP]) being the primary measure. Secondary measures included neurocognitive tasks related to driving. Performance differences between groups were compared to those of blood alcohol concentrations of 0.5 mg/ml to determine clinical relevance. Results: Compared to controls, mean increase in SDLP of all antidepressant users was not significant, nor clinically relevant (+0.75 cm, 95% CI: - 0.83 cm; +2.33 cm). However, users treated less than 3 years (n = 20) did show a significant and clinically relevant increase in SDLP (+2.05 cm). No significant effects were observed on neurocognitive tasks for any user group, although large individual differences were present. Most results from neurocognitive tests were inconclusive, while a few parameters confirmed non‐inferiority for users treated longer than 3 years. Conclusion: The impairing effects of antidepressant treatment on driving performance and neurocognition mitigate over time following long‐term use of 3 years
Impact of junction length on supercurrent resilience against magnetic field in InSb-Al nanowire Josephson junctions
Semiconducting nanowire Josephson junctions represent an attractive platform
to investigate the anomalous Josephson effect and detect topological
superconductivity by studying Josephson supercurrent. However, an external
magnetic field generally suppresses the supercurrent through hybrid nanowire
junctions and significantly limits the field range in which the supercurrent
phenomena can be studied. In this work, we investigate the impact of the length
of InSb-Al nanowire Josephson junctions on the supercurrent resilience against
magnetic fields. We find that the critical parallel field of the supercurrent
can be considerably enhanced by reducing the junction length. Particularly, in
30 nm-long junctions supercurrent can persist up to 1.3 T parallel field -
approaching the critical field of the superconducting film. Furthermore, we
embed such short junctions into a superconducting loop and obtain the
supercurrent interference at a parallel field of 1 T. Our findings are highly
relevant for multiple experiments on hybrid nanowires requiring a magnetic
field-resilient supercurrent.Comment: 17 pages, 5 figures in main text. 22 pages, 10 figures in supporting
informatio
Quantized Majorana conductance
Majorana zero-modes hold great promise for topological quantum computing.
Tunnelling spectroscopy in electrical transport is the primary tool to identify
the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in
differential-conductance. The Majorana ZBP-height is predicted to be quantized
at the universal conductance value of 2e2/h at zero temperature. Interestingly,
this quantization is a direct consequence of the famous Majorana symmetry,
'particle equals antiparticle'. The Majorana symmetry protects the quantization
against disorder, interactions, and variations in the tunnel coupling. Previous
experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent
observation of a peak-height close to 2e2/h. Here, we report a quantized
conductance plateau at 2e2/h in the zero-bias conductance measured in InSb
semiconductor nanowires covered with an Al superconducting shell. Our
ZBP-height remains constant despite changing parameters such as the magnetic
field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish
this quantized Majorana peak from possible non-Majorana origins, by
investigating its robustness on electric and magnetic fields as well as its
temperature dependence. The observation of a quantized conductance plateau
strongly supports the existence of non-Abelian Majorana zero-modes in the
system, consequently paving the way for future braiding experiments.Comment: 5 figure
Electric field tunable superconductor-semiconductor coupling in Majorana nanowires
We study the effect of external electric fields on
superconductor-semiconductor coupling by measuring the electron transport in
InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor.
We find that the gate voltage induced electric fields can greatly modify the
coupling strength, which has consequences for the proximity induced
superconducting gap, effective g-factor, and spin-orbit coupling, which all
play a key role in understanding Majorana physics. We further show that level
repulsion due to spin-orbit coupling in a finite size system can lead to
seemingly stable zero bias conductance peaks, which mimic the behavior of
Majorana zero modes. Our results improve the understanding of realistic
Majorana nanowire systems.Comment: 10 pages, 5 figures, supplemental information as ancillary fil
Controlled crossed Andreev reflection and elastic co-tunneling mediated by Andreev bound states
A short superconducting segment can couple attached quantum dots via elastic
co-tunneling (ECT) and crossed Andreev reflection (CAR). Such coupled quantum
dots can host Majorana bound states provided that the ratio between CAR and ECT
can be controlled. Metallic superconductors have so far been shown to mediate
such tunneling phenomena, albeit with limited tunability. Here we show that
Andreev bound states formed in semiconductor-superconductor heterostructures
can mediate CAR and ECT over mesoscopic length scales. Andreev bound states
possess both an electron and a hole component, giving rise to an intricate
interference phenomenon that allows us to tune the ratio between CAR and ECT
deterministically. We further show that the combination of intrinsic spin-orbit
coupling in InSb nanowires and an applied magnetic field provides another
efficient knob to tune the ratio between ECT and CAR and optimize the amount of
coupling between neighboring quantum dots
Beïnvloeding van de rijvaardigheid bij langdurig gebruik van ICADTS-categorie III geneesmiddelen
An explorative approach to understanding individual differences in driving performance and neurocognition in long-term benzodiazepine users
Objective: Previous research reported cognitive and psychomotor impairments in long‐term users of benzodiazepine receptor agonists (BZRAs). This article explores the role of acute intoxication and clinical complaints. Methods: Neurocognitive and on‐road driving performance of 19 long‐term (≥6 months) regular (≥twice weekly) BZRA users with estimated plasma concentrations, based on self‐reported use, exceeding the therapeutic threshold (CBZRA+), and 31 long‐term regular BZRA users below (CBZRA−), was compared to that of 76 controls. Results: BZRA users performed worse on tasks of response speed, processing speed, and sustained attention. Age, but not CBZRA or self‐reported clinical complaints, was a significant covariate. Road‐tracking performance was explained by CBZRA only. The CBZRA + group exhibited increased mean standard deviation of lateral position comparable to that at blood‐alcohol concentrations of 0.5 g/L. Conclusions: Functional impairments in long‐term BZRA users are not attributable to self‐reported clinical complaints or estimated BZRA concentrations, except for road‐tracking, which was impaired in CBZRA + users. Limitations to address are the lack of assessment of objective clinical complaints, acute task related stress, and actual BZRA plasma concentrations. In conclusion, the results confirm previous findings that demonstrate inferior performance across several psychomotor and neurocognitive domains in long‐term BZRA users
Deterministic Evolutionary Trajectories Influence Primary Tumor Growth: TRACERx Renal.
The evolutionary features of clear-cell renal cell carcinoma (ccRCC) have not been systematically studied to date. We analyzed 1,206 primary tumor regions from 101 patients recruited into the multi-center prospective study, TRACERx Renal. We observe up to 30 driver events per tumor and show that subclonal diversification is associated with known prognostic parameters. By resolving the patterns of driver event ordering, co-occurrence, and mutual exclusivity at clone level, we show the deterministic nature of clonal evolution. ccRCC can be grouped into seven evolutionary subtypes, ranging from tumors characterized by early fixation of multiple mutational and copy number drivers and rapid metastases to highly branched tumors with >10 subclonal drivers and extensive parallel evolution associated with attenuated progression. We identify genetic diversity and chromosomal complexity as determinants of patient outcome. Our insights reconcile the variable clinical behavior of ccRCC and suggest evolutionary potential as a biomarker for both intervention and surveillance
New genetic loci link adipose and insulin biology to body fat distribution.
Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms
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