The field of quantum computing has grown from concept to demonstration devices over the past 20 years. Universal quantum computing offers efficiency in approaching problems of scientific and ...commercial interest, such as factoring large numbers, searching databases, simulating intractable models from quantum physics, and optimizing complex cost functions. Here, we present an 11-qubit fully-connected, programmable quantum computer in a trapped ion system composed of 13
Yb
ions. We demonstrate average single-qubit gate fidelities of 99.5Formula: see text, average two-qubit-gate fidelities of 97.5Formula: see text, and SPAM errors of 0.7Formula: see text. To illustrate the capabilities of this universal platform and provide a basis for comparison with similarly-sized devices, we compile the Bernstein-Vazirani and Hidden Shift algorithms into our native gates and execute them on the hardware with average success rates of 78Formula: see text and 35Formula: see text, respectively. These algorithms serve as excellent benchmarks for any type of quantum hardware, and show that our system outperforms all other currently available hardware.
Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of ...measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such 'squeezed states' of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light-matter interaction.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Understanding the cognitive and emotional mechanisms that link autistic traits and risk for suicide is a vital next step for research and clinical practice. This study included a broad sample of ...adult women (n = 74) who report finding social situations confusing and/or exhausting, and who score high on measures of autistic traits. Regardless of autism diagnostic status, these women reported high rates of suicidal thoughts and behaviors. Depression symptoms were more associated with suicidality than were autistic trait measures of social communication. Measures of neurotypical “imagination” and of repetitive behavior likewise were associated with suicidality risk. Simultaneously feeling sad and feeling stuck or unable to imagine alternate strategies, may uniquely increase suicide risk in autism.
Summary Background The causes of phenotypic heterogeneity in familial Alzheimer's disease with autosomal dominant inheritance are not well understood. We aimed to characterise clinical phenotypes and ...genetic associations with APP and PSEN1 mutations in symptomatic autosomal dominant familial Alzheimer's disease (ADAD). Methods We retrospectively analysed genotypic and phenotypic data (age at symptom onset, initial cognitive or behavioural symptoms, and presence of myoclonus, seizures, pyramidal signs, extrapyramidal signs, and cerebellar signs) from all individuals with ADAD due to APP or PSEN1 mutations seen at the Dementia Research Centre in London, UK. We examined the frequency of presenting symptoms and additional neurological features, investigated associations with age at symptom onset, APOE genotype, and mutation position, and explored phenotypic differences between APP and PSEN1 mutation carriers. The proportion of individuals presenting with various symptoms was analysed with descriptive statistics, stratified by mutation type. Findings Between July 1, 1987, and Oct 31, 2015, age at onset was recorded for 213 patients (168 with PSEN1 mutations and 45 with APP mutations), with detailed history and neurological examination findings available for 121 (85 with PSEN1 mutations and 36 with APP mutations). We identified 38 different PSEN1 mutations (four novel) and six APP mutations (one novel). Age at onset differed by mutation, with a younger onset for individuals with PSEN1 mutations than for those with APP mutations (mean age 43·6 years SD 7·2 vs 50·4 years SD 5·2, respectively, p<0·0001); within the PSEN1 group, 72% of age at onset variance was explained by the specific mutation. A cluster of five mutations with particularly early onset (mean age at onset <40 years) involving PSEN1's first hydrophilic loop suggests critical functional importance of this region. 71 (84%) individuals with PSEN1 mutations and 35 (97%) with APP mutations presented with amnestic symptoms, making atypical cognitive presentations significantly more common in PSEN1 mutation carriers (n=14; p=0·037). Myoclonus and seizures were the most common additional neurological features; individuals with myoclonus (40 47% with PSEN1 mutations and 12 33% with APP mutations) were significantly more likely to develop seizures (p=0·001 for PSEN1; p=0·036 for APP ), which affected around a quarter of the patients in each group (20 24% and nine 25%, respectively). A number of patients with PSEN1 mutations had pyramidal (21 25%), extrapyramidal (12 14%), or cerebellar (three 4%) signs. Interpretation ADAD phenotypes are heterogeneous, with both age at onset and clinical features being influenced by mutation position as well as causative gene. This highlights the importance of considering genetic testing in young patients with dementia and additional neurological features in order to appropriately diagnose and treat their symptoms, and of examining different mutation types separately in future research. Funding Medical Research Council and National Institute for Health Research.
Context
In pregnancy, vitamin D insufficiency and deficiency, defined as serum 25‐hydroxyvitamin D (25(OH)D) <50 nM, and <25 nM, respectively, may have adverse effects for both mother and child. ...Prevalence estimates, and identification of subgroups at special risk, may be useful for the planning of preventive strategies.
Objective
To study the prevalence and risk factors of hypovitaminosis D in early pregnancy.
Design and Methods
In a cross‐sectional study of 1348 women in early pregnancy from the Odense Child Cohort, Denmark, 25(OH)D was determined and correlated to demographic and lifestyle variables (age, nationality, skin tone, parity, prepregnancy body mass index (BMI), smoking and sun exposure), using multiple linear and logistic regression analyses for all year, or stratified for summer and winter. The risk of vitamin D insufficiency was expressed as odds ratios (OR) with 95% confidence intervals in brackets.
Results
The prevalence of vitamin D insufficiency and deficiency was estimated to 27·8% and 3·5% respectively. In adjusted analyses, vitamin D insufficiency was directly associated with winter season, OR = 1·89 (1·35–2·63); increasing prepregnancy BMI, OR = 1·06 (1·03–1·10); and smoking, OR = 2·7 (1·34–5·41); but was less frequent in nulliparous, OR = 0·47 (0·33–0·68) and tanned Caucasians, OR = 0·63 (0·41–0·97). Season‐specific associations having parental origin from outside Europe in summer, OR = 4·13 (1·41–12·13); in winter smoking, OR = 3·15 (1·19–8·36); and prepregnancy BMI, OR = 1·12 (1·06–1·18).
Conclusions
Vitamin D insufficiency was widespread in early pregnancy. Associations to smoking, prepregnancy BMI and origin outside Europe varied with season. Multiparity and not being tanned in Caucasians represent new risk factors of vitamin D insufficiency.
Depletion of intracellular calcium stores activates store-operated calcium entry across the plasma membrane in many cells. STIM1, the putative calcium sensor in the endoplasmic reticulum, and the ...calcium release-activated calcium (CRAC) modulator CRACM1 (also known as Orai1) in the plasma membrane have recently been shown to be essential for controlling the store-operated CRAC current (ICRAC). However, individual overexpression of either protein fails to significantly amplify ICRAC. Here, we show that STIM1 and CRACM1 interact functionally. Overexpression of both proteins greatly potentiates ICRAC, suggesting that STIM1 and CRACM1 mutually limit store-operated currents and that CRACM1 may be the long-sought CRAC channel.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Chk1 both arrests replication forks and enhances repair of DNA damage by phosphorylating downstream effectors. Although there has been a concerted effort to identify effectors of Chk1 activity, ...underlying mechanisms of effector action are still being identified. Metnase (also called SETMAR) is a SET and transposase domain protein that promotes both DNA double-strand break (DSB) repair and restart of stalled replication forks. In this study, we show that Metnase is phosphorylated only on Ser495 (S495) in vivo in response to DNA damage by ionizing radiation. Chk1 is the major mediator of this phosphorylation event. We had previously shown that wild-type (wt) Metnase associates with chromatin near DSBs and methylates histone H3 Lys36. Here we show that a Ser495Ala (S495A) Metnase mutant, which is not phosphorylated by Chk1, is defective in DSB-induced chromatin association. The S495A mutant also fails to enhance repair of an induced DSB when compared with wt Metnase. Interestingly, the S495A mutant demonstrated increased restart of stalled replication forks compared with wt Metnase. Thus, phosphorylation of Metnase S495 differentiates between these two functions, enhancing DSB repair and repressing replication fork restart. In summary, these data lend insight into the mechanism by which Chk1 enhances repair of DNA damage while at the same time repressing stalled replication fork restart.
Abstract
The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy and interferometry, ...can be combined. The K2 mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and CCD saturation, as well as restrictions on data storage and bandwidth, limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, which we call halo photometry, to observe very bright stars using a limited number of pixels. Halo photometry is simple, fast and does not require extensive pixel allocation, and will allow us to use K2 and other photometric missions, such as TESS, to observe very bright stars for asteroseismology and to search for transiting exoplanets. We apply this method to the seven brightest stars in the Pleiades open cluster. Each star exhibits variability; six of the stars show what are most likely slowly pulsating B-star pulsations, with amplitudes ranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of combining K2 photometry with spectroscopy and interferometry to show that it is not a ‘Maia variable’, and to establish that its variability is caused by rotational modulation of a large chemical spot on a 10 d time-scale.
A major obstacle to interpreting the rotation period distribution for main-sequence stars from Kepler mission data has been the lack of a precise evolutionary status for these objects. We address ...this by investigating the evolutionary status based on Gaia Data Release 2 parallaxes and photometry for more than 30,000 Kepler stars with rotation period measurements. Many of these are subgiants and should be excluded in future work on dwarfs. We particularly investigate a 193-star sample of solar analogs and report newly determined rotation periods for 125 of these. These include 54 stars from a prior sample, of which we can confirm the periods for 50. The remainder are new, and 10 of them longer than a solar rotation period, suggesting that Sun-like stars continue to spin down on the main sequence past solar age. Our sample of solar analogs could potentially serve as a benchmark for future missions, such as PLAnetary Transits and Oscillations of stars, and emphasizes the need for additional astrometric, photometric, and spectroscopic information before interpreting the stellar populations and results from time series surveys.
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