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A quantum simulation platform based on quantum dots is reported that can operate at relatively low temperatures, and its utility is shown by simulating a Fermi–Hubbard model. Quantum simulations on quantum dots Quantum simulations have been performed on various different platforms, for example using vacancies in diamond or ultracold quantum gases. Quantum dots have been regarded as a promising constituent of quantum simulation platforms for some time, but owing to difficulties in calibrating them it has so far been impossible to run a successful simulation. Here, the authors overcome these difficulties and demonstrate a quantum simulation of a Fermi–Hubbard model, which is a famous model in condensed matter physics. Quantum simulation platforms based on quantum dots are predicted to be able to reach lower temperatures than atomic-physics-based platforms. This could help to clarify puzzles in condensed matter physics, such as high-temperature superconductivity. Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter 1 , 2 , 3 . Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi–Hubbard models 4 , 5 , 6 . Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi–Hubbard Hamiltonian 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 . Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi–Hubbard physics on solid-state platforms have been made 18 , 19 . Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi–Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition 20 , which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition 1 . As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

Electrostatically defined quantum dot arrays offer a compelling platform for quantum computation and simulation. However, tuning up such arrays with existing techniques becomes impractical when going beyond a handful of quantum dots. Here, we present a method for systematically adding quantum dots to an array one dot at a time, in such a way that the number of electrons on previously formed dots is unaffected. The method allows individual control of the number of electrons on each of the dots, as well as of the interdot tunnel rates. We use this technique to tune up a linear array of eight GaAs quantum dots such that they are occupied by one electron each. This new method overcomes a critical bottleneck in scaling up quantum-dot based qubit registers.

Introduction A somatic disorder may initially be overlooked when a child presents with psychiatric symptoms. We report two children with anorexia nervosa as initial diagnosis and in whom there was a delay in the final diagnosis of the underlying malignancy. A literature survey was performed including patients under 18 years of age with psychiatric symptoms in whom later on an oncological diagnosis became evident as an explanation. Results We have found 30 additional cases, with a median delay of 12 months until the diagnosis of the tumour. Overall, 16 boys and 16 girls had a solid tumour: 26 central nervous system tumours, 3 tumours of the gastrointestinal tract and 3 others. In 25 out of 32 patients anorexia nervosa was assumed, although it always appeared to be atypical. Patients younger than 7 years had a significantly longer delay until final diagnosis, while no other patient characteristics correlated with such delay. Discussion In addition to careful physical (including full neurological) examination, we advise additional neuroimaging especially in each case of atypical presentation of anorexia nervosa, in order to avoid a delay in diagnosis of a possible malignancy. Furthermore, it is desirable to perform a re-examination when a psychiatric disorder does not respond to therapy, in order not to overlook an underlying oncological disease.

Electrostatic confinement in semiconductors provides a flexible platform for the emulation of interacting electrons in a two-dimensional lattice, including in the presence of gauge fields. This combination offers the potential to realize a wide host of quantum phases. Here we present a measurement and fabrication scheme that builds on capacitance spectroscopy and allows for the independent control of density and periodic potential strength imposed on a two-dimensional electron gas. We characterize disorder levels and (in)homogeneity and develop and optimize different gating strategies at length scales where interactions are expected to be strong. A continuation of these ideas might see to fruition the emulation of interaction-driven Mott transitions or Hofstadter butterfly physics.

Electrostatically defined quantum dot arrays offer a compelling platform for quantum computation and simulation. However, tuning up such arrays with existing techniques becomes impractical when going beyond a handful of quantum dots. Here, we present a method for systematically adding quantum dots to an array one dot at a time, in such a way that the number of electrons on previously formed dots is unaffected. The method allows individual control of the number of electrons on each of the dots, as well as of the interdot tunnel rates. We use this technique to tune up a linear array of eight GaAs quantum dots such that they are occupied by one electron each. This new method overcomes a critical bottleneck in scaling up quantum-dot based qubit registers.

Interacting fermions on a lattice can develop strong quantum correlations, which lie at the heart of the classical intractability of many exotic phases of matter. Seminal efforts are underway in the control of artificial quantum systems, that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical pure-state initialisation and readily adhere to an engineerable Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder inherent to solid state has made attempts at emulating Fermi-Hubbard physics on solid-state platforms few and far between. Here, we show that for gate-defined quantum dots, this disorder can be suppressed in a controlled manner. Novel insights and a newly developed semi-automated and scalable toolbox allow us to homogeneously and independently dial in the electron filling and nearest-neighbour tunnel coupling. Bringing these ideas and tools to fruition, we realize the first detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here show how quantum dots can be used to investigate the physics of ever more complex many-body states.

Background. Mortality among patients with Clostridium difficile infection (CDI) is high. Because of high age and multiple underlying diseases, CDI-related mortality is difficult to estimate. We estimated CDI-related mortality in an endemic situation, not influenced by outbreaks and consequently certain patients and C. difficile strains. Methods. Between 2006 and 2009, 13 Dutch hospitals included all hospitalized CDI patients. Nine hospitals individually matched each CDI patient to 2 control patients, based on ward and time of CDI hospitalization. Survival status was obtained via the Dutch Civil Registration System. Kaplan-Meier and Cox regression were used for survival analysis. Results. We identified 1366 patients with CDI (1.33 per 1000 admissions). All-cause mortality risk was 13% after 30 days and 37% after 1 year. The highest mortality was seen among elderly patients and patients with polymerase chain reaction ribotype 027. Three hundred seventeen CDI patients were matched to 317 patients without diarrhea and 232 patients with diarrhea, with a 30-day mortality risk of 5.4% and 8.6%, respectively. CDI patients had a 2.5-fold increased 30-day mortality rate compared to controls without diarrhea (hazard ratio 2.5 [95% confidence interval, 1.4–4.3]) when adjusted for age, sex, and underlying diseases. CDI-related death occurred mainly within 30 days after diagnosis. Conclusions. Mortality among CDI patients is high, even in an endemic situation. Our results show that CDI is associated with to a 2.5-fold increase in 30-day mortality. This highlights the considerable disease burden and clinical impact of CDI, even in absence of an outbreak.

Clostridium difficile is the most common cause of antibiotic-associated diarrhoea in hospitals and other healthcare facilities. The elderly are particularly susceptible and at increased risk for adverse outcome as a result of C. difficile infection. The aim of this study was to determine the prevalence of C. difficile colonization among residents of nursing homes in Hesse and to compare it with the prevalence in the general population living outside long-term care facilities (LTCF). We assessed possible risk factors for C. difficile colonization and determined the genotype of circulating strains. C. difficile was isolated from 11/240 (4.6%) nursing home residents and 2/249 (0.8%) individuals living outside LTCF (p = 0.02). Ten of 11 (90.9%) isolates from nursing homes and one of two isolates from the population outside LTCF were toxigenic. The prevalence of C. difficile colonization varied from 0% to 10% between different nursing homes. Facilities with known actual or recent CDI cases were more likely to have colonized residents than facilities without known CDI cases. C. difficile PCR-ribotypes 014 and 001 were the most prevalent genotypes and accounted for 30% and 20% of toxigenic isolates in nursing homes, respectively. Interestingly, no individuals carried the epidemic strain PCR-ribotype 027. Our results suggest that residents of nursing homes in Germany are at high risk for colonization by virulent C. difficile strains. The high prevalence of C. difficile colonization in nursing homes underscores the importance of good adherence to standard infection control precautions even in the absence of a diagnosed infection. They also emphasize the need for specific programs to increase the awareness of healthcare professionals in LTCF for CDI.

Background: In recent decades, the number of immunocompromised patients (ICPs) has increased significantly. ICPs have an impaired immune system, making them susceptible to complicated infections. To protect them from infections, ICPs are eligible to receive several medically indicated vaccines. To obtain insight into the uptake of these medically indicated vaccines, we determined the coverage of these vaccines in ICPs. Methods: This observational cohort study was conducted at the University Medical Centre Utrecht, the Netherlands, from September 2021 to April 2022. All adult ICPs admitted for COVID-19 were asked to complete a questionnaire on their vaccination history (pneumococcal, herpes zoster, human papillomavirus vaccination, influenza, and COVID-19 vaccines) and history of vaccine-preventable infections. In addition, patients’ vaccination history was reviewed in medical files. Results: A total of 115 patients completed the questionnaire and were included. Although all patients had an indication for pneumococcal vaccination, only 22 received it (19%). Coverage for herpes zoster was low (1%, 1/106 eligible patients). Coverage for human papillomavirus vaccination (HPV) was also low (40%, two out of five eligible patients). In contrast, 92% of patients received vaccination against SARS-CoV-2, and 77% of patients received seasonal influenza vaccination. Conclusions: Although coverage for influenza and COVID-19 vaccination was high in ICPs, coverage for other medically indicated vaccines was low. Identifying which factors contributed to high COVID-19 and influenza vaccine uptake can help to improve vaccination rates for the other recommended vaccines. Clear guidelines for clinicians and the removal of organizational obstacles are needed to improve vaccination coverage.