Efficient orthogonal control of tunnel couplings in a quantum dot array

Electrostatically-defined semiconductor quantum dot arrays offer a promising platform for quantum computation and quantum simulation. However, crosstalk of gate voltages to dot potentials and inter-dot tunnel couplings complicates the tuning of the device parameters. To date, crosstalk to the dot potentials is routinely and efficiently compensated using so-called virtual gates, which are specific linear combinations of physical gate voltages. However, due to exponential dependence of tunnel couplings on gate voltages, crosstalk to the tunnel barriers is currently compensated through a slow iterative process. In this work, we show that the crosstalk on tunnel barriers can be efficiently characterized and compensated for, using the fact that the same exponential dependence applies to all gates. We demonstrate efficient calibration of crosstalk in a quadruple quantum dot array and define a set of virtual barrier gates, with which we show orthogonal control of all inter-dot tunnel couplings. Our method marks a key step forward in the scalability of the tuning process of large-scale quantum dot arrays.Comment: 8 pages, 7 figure

Automated tuning of inter-dot tunnel couplings in quantum dot arrays

Semiconductor quantum dot arrays defined electrostatically in a 2D electron gas provide a scalable platform for quantum information processing and quantum simulations. For the operation of quantum dot arrays, appropriate voltages need to be applied to the gate electrodes that define the quantum dot potential landscape. Tuning the gate voltages has proven to be a time-consuming task, because of initial electrostatic disorder and capacitive cross-talk effects. Here, we report on the automated tuning of the inter-dot tunnel coupling in a linear array of gate-defined semiconductor quantum dots. The automation of the tuning of the inter-dot tunnel coupling is the next step forward in scalable and efficient control of larger quantum dot arrays. This work greatly reduces the effort of tuning semiconductor quantum dots for quantum information processing and quantum simulation

Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array

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

State-of-the-Art bewaarsysteem tulpenbollen : Resultaten 2010

Het project State-of-the-Art bewaren van tulpenbollen is in 2007 opgestart om te demonstreren wat er met behoud of verbetering van productkwaliteit, met de huidige stand der techniek aan energiebesparing mogelijk is. En om met aanvullend onderzoek op de deelnemende bloembollenbedrijven in de toekomst nog meer te kunnen besparen. Voor het 4de jaar op rij is er door de nu 10 deelnemers fors bespaard op energie: gemiddeld 30% op gas en 44% op elektra. Op het bedrijf dat het meest op gas bespaarde was dat zelfs 72% en op het bedrijf dat het meest op elektra bespaarde was dat 80%. Het doel van het project is tweeledig: Spoor 1) demonstreren wat er met behoud of verbetering van de productkwaliteit met de huidige stand der techniek aan energiebesparing in de bewaring bij tulp mogelijk is. Spoor 2) aanvullend onderzoek & ontwikkeling om hierbij in de toekomst nog meer energie te kunnen besparen

Methodological concepts for integrated assessment of agricultural and environmental policies in SEAMLESS-IF

Agricultural and Food Policy, Environmental Economics and Policy, Farm Management, Land Economics/Use,

Efficacy of OptiphosTM phytase on mineral digestibility in diets for breeding sows: effect during pregnancy an lactation

Phosphorus in most diets for breeding sows is digested for 20 to 40%, thus leading to a relatively high amount of P in the manure. To enhance the P digestibility in diets for both lactating and gestating sows, two separate experiments were carried out to study the efficacy of OptiphosTM phytase derived from E. coli and produced by the yeast Pichia pastoris. Thirty crossbred gestating sows and 36 lactating sows were used in these studies. Five treatments were imposed on the gestating sows: 1) a negative control treatment, based on a low-P diet without added feed phosphate and microbial phytase. Diets in Treatments 2, 3 and 4 were the same as the negative control diet, except that an amount of Optiphos phytase of 125, 250 and 1,000 U.kg-1 of diet, respectively, was added. Treatment 5 was the positive control diet, based on the same diet with 1.0 g of added digestible P.kg-1 of diet from monocalcium phosphate. The lactating sows of Treatments 1 to 6 received a negative control diet, the same diet with an amount of OptiphosTM phytase of 125, 250, 500 and 1000 U.kg-1 of diet and a positive control diet supplemented with 1.5 g of digestible P.kg-1, respectively. The negative control diets were different in ingredient composition because of the different nutrient requirements between lactating and gestating sows. The ratio between Ca and digestible P was kept at 2.8:1 and 3.3:1 for the lactating and gestating diets, respectively, with a minimum of 5.0 g Ca.kg-1. Feeding level of the sows was according to Dutch recommendations. Six sows per treatment were used. The lactating sows received the diets from 2 weeks before farrowing until weaning of the piglets at 4 weeks of age and the gestating sows from day 49 to day 100 of pregnancy. Faecal samples of the sows were collected by rectal stimulation on days 14 and 21 post-farrowing, and on days 70 and 100 of pregnancy. Digestibility coefficients of dry matter, organic matter, ash and the minerals under investigation were calculated using Cr2O3 as an indigestible marker. In addition, several performance characteristics were registered. Phosphorus digestibility was clearly enhanced by the addition of microbial phytase to the lactating sow diets, as was the digestibility of ash, Ca, Na, K, Cu, and Zn. In the gestating sows only digestibility of P was significantly enhanced by microbial phytase. In both gestating and lactating sows the lowest level of phytase addition (125 U.kg-1 of diet) already resulted in the highest response in P digestibility without further improvement at higher phytase inclusion levels. The additional amount of digestible P absorbed with a phytase supplement of 125 or more U.kg-1 in lactating sows was on average 0.90 g/kg. An average amount of 0.36 and 0.67 g digestible P.kg-1 was generated in gestating sows at day 70 and day 100 of pregnancy by this phytase inclusion, respectively. No signs of any adverse effect of phytase on sow or piglet health and performance were observed. OptiphosTM phytase was already highly effective at a dose of 125 U.kg-1 of diet. Possible reasons for the lack of further improvement of P digestibility at higher doses of phytase are discussed. If feed phosphates are (partly) replaced by 125 U phytase.kg-1 of diet, then P excretion can be reduced by 0.85 kg.sow-1.year-1

Prediction meets causal inference: the role of treatment in clinical prediction models

In this paper we study approaches for dealing with treatment when developing a clinical prediction model. Analogous to the estimand framework recently proposed by the European Medicines Agency for clinical trials, we propose a ‘predictimand’ framework of different questions that may be of interest when predicting risk in relation to treatment started after baseline. We provide a formal definition of the estimands matching these questions, give examples of settings in which each is useful and discuss appropriate estimators including their assumptions. We illustrate the impact of the predictimand choice in a dataset of patients with end-stage kidney disease. We argue that clearly defining the estimand is equally important in prediction research as in causal inference

Extensive Study of Breast Milk and Infant Growth: Protocol of the Cambridge Baby Growth and Breastfeeding Study (CBGS-BF).

Funder: Medical Research Council; Grant(s): Unit programmes: MC_UU_12015/2 and MC_UU_00006/2Funder: Wellcome TrustGrowth and nutrition during early life have been strongly linked to future health and metabolic risks. The Cambridge Baby Growth Study (CBGS), a longitudinal birth cohort of 2229 mother-infant pairs, was set up in 2001 to investigate early life determinant factors of infant growth and body composition in the UK setting. To carry out extensive profiling of breastmilk intakes and composition in relation to infancy growth, the Cambridge Baby Growth and Breastfeeding Study (CBGS-BF) was established upon the original CBGS. The strict inclusion criteria were applied, focusing on a normal birth weight vaginally delivered infant cohort born of healthy and non-obese mothers. Crucially, only infants who were exclusively breastfed for the first 6 weeks of life were retained in the analysed study sample. At each visit from birth, 2 weeks, 6 weeks, and then at 3, 6, 12, 24, and 36 months, longitudinal anthropometric measurements and blood spot collections were conducted. Infant body composition was assessed using air displacement plethysmography (ADP) at 6 weeks and 3 months of age. Breast milk was collected for macronutrients and human milk oligosaccharides (HMO) measurements. Breast milk intake volume was also estimated, as well as sterile breastmilk and infant stool collection for microbiome study