Single-shot readout of electron spin states in a quantum dot using spin-dependent tunnel rates

We present a method for reading out the spin state of electrons in a quantum dot that is robust against charge noise and can be used even when the electron temperature exceeds the energy splitting between the states. The spin states are first correlated to different charge states using a spin dependence of the tunnel rates. A subsequent fast measurement of the charge on the dot then reveals the original spin state. We experimentally demonstrate the method by performing read-out of the two-electron spin states, achieving a single-shot visibility of more than 80%. We find very long triplet-to-singlet relaxation times (up to several milliseconds), with a strong dependence on in-plane magnetic field.Comment: 4 pages, 4 figure

Control and Detection of Singlet-Triplet Mixing in a Random Nuclear Field

We observe mixing between two-electron singlet and triplet states in a double quantum dot, caused by interactions with nuclear spins in the host semiconductor. This mixing is suppressed by applying a small magnetic field, or by increasing the interdot tunnel coupling and thereby the singlet-triplet splitting. Electron transport involving transitions between triplets and singlets in turn polarizes the nuclei, resulting in striking bistabilities. We extract from the fluctuating nuclear field a limitation on the time-averaged spin coherence time T2* of 25 ns. Control of the electron-nuclear interaction will therefore be crucial for the coherent manipulation of individual electron spins.Comment: 4 pages main text, 4 figure

The impact of reduction of doublet well spacing on the Net Present Value and the life time of fluvial Hot Sedimentary Aquifer doublets

This paper evaluates the impact of reduction of doublet well spacing, below the current West Netherlands Basin standard of 1000 to 1500 m, on the Net Present Value (NPV) and the life time of fluvial Hot Sedimentary Aquifer (HSA) doublets. First, a sensitivity analysis is used to show the possible advantage of such reduction on the NPV. The parameter value ranges are derived from West Netherlands Basin HSA doublet examples. The results indicate that a reduction of well spacing from 1400 to 1000 m could already influence NPV by up to 15%. This effect would be larger in more marginally economic HSA doublets compared to the West Netherlands Basin base case scenario. The possibility to reduce well spacing is supported by finite element production simulations, utilizing detailed facies architecture models. Furthermore, our results underline the necessity of detailed facies architecture models to assess the potential and risks of HSA doublets. This factor significantly affects doublet life time and net energy production of the doublet

Spin filling of a quantum dot derived from excited-state spectroscopy

We study the spin filling of a semiconductor quantum dot using excited-state spectroscopy in a strong magnetic field. The field is oriented in the plane of the two-dimensional electron gas in which the dot is electrostatically defined. By combining the observation of Zeeman splitting with our knowledge of the absolute number of electrons, we are able to determine the ground state spin configuration for one to five electrons occupying the dot. For four electrons, we find a ground state spin configuration with total spin S=1, in agreement with Hund's first rule. The electron g-factor is observed to be independent of magnetic field and electron number.Comment: 11 pages, 7 figures, submitted to New Journal of Physics, focus issue on Solid State Quantum Informatio

Calibration of the LIGO displacement actuators via laser frequency modulation

We present a frequency modulation technique for calibration of the displacement actuators of the LIGO 4-km-long interferometric gravitational-wave detectors. With the interferometer locked in a single-arm configuration, we modulate the frequency of the laser light, creating an effective length variation that we calibrate by measuring the amplitude of the frequency modulation. By simultaneously driving the voice coil actuators that control the length of the arm cavity, we calibrate the voice coil actuation coefficient with an estimated 1-sigma uncertainty of less than one percent. This technique enables a force-free, single-step actuator calibration using a displacement fiducial that is fundamentally different from those employed in other calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit

The influence of facies heterogeneity on the doublet performance in low-enthalpy geothermal sedimentary reservoirs

AbstractA three-dimensional model is used to study the influence of facies heterogeneity on energy production under different operational conditions of low-enthalpy geothermal doublet systems. Process-based facies modelling is utilised for the Nieuwerkerk sedimentary formation in the West Netherlands Basin to construct realistic reservoir models honouring geological heterogeneity. A finite element based reservoir simulator is used to model the fluid flow and heat transfer over time. A series of simulations is carried out to examine the effects of reservoir heterogeneity (Net-to-Gross ratio, N/G) on the life time and the energy recovery rate for different discharge rates and the production temperature (Tmin) above which the doublet is working. With respect to the results, we propose a design model to estimate the life time and energy recovery rate of the geothermal doublet. The life time is estimated as a function of N/G, Tmin and discharge rate, while the design model for the energy recovery rate is only a function of N/G and Tmin. Both life time and recovery show a positive relation with an increasing N/G. Further our results suggest that neglecting details of process-based facies modelling may lead to significant errors in predicting the life time of low-enthalpy geothermal systems for N/G values below 70%

Failing Homeostasis of Quadriceps Muscle Energy- and pH Balance During Bicycling in a Young Patient With a Fontan Circulation

Aims: Patients with a congenital heart condition palliated with a Fontan circulation generally present with decreased exercise capacity due to impaired cardiopulmonary function. Recently, a study in patients with a Fontan circulation reported evidence for abnormal vascular endothelial function in legmuscle. We investigated if abnormal skeletal muscle hemodynamics during exercise play a role in the limited exercise tolerance of Fontan patients. If so, abnormalities in intramuscular energy metabolism would be expected both during exercise as well as during post-exercise metabolic recovery. Methods: In a young patient with a Fontan circulation and his healthy twin brother we studied the in vivo dynamics of energy-and pH-balance in quadriceps muscle during and after a maximal in-magnet bicycling exercise challenge using 31-phosphorus magnetic resonance spectroscopy. An unrelated age-matched boy was also included as independent control. Results: Quadriceps phosphocreatine (PCr) depletion during progressive exercise was more extensive in the Fontan patient than in both controls (95% vs. 80%, respectively). Importantly, it failed to reach an intermittent plateau phase observed in both controls. Quadriceps pH during exercise in the Fontan patient fell 0.3 units at low to moderate workloads, dropping to pH 6.6 at exhaustion. In both controls quadriceps acidification during exercise was absent but for the maximal workload in the twin brother (pH 6.8). Post-exercise, the rate of metabolic recovery in the Fontan patient and both controls was identical (time constant of PCr recovery 32 +/- 4, 31 +/- 2, and 28 +/- 4 s, respectively). Conclusion: Homeostasis of quadriceps energy- and pH-balance during a maximal exercise test failed in the Fontan patient in comparison to his healthy twin brother and an age-matched independent control. Post-exercise metabolic recovery was normal which does not support the contribution of significant endothelial dysfunction affecting adequate delivery of oxidative substrates to the muscle to the lower exercise capacity in this particular Fontan patient. These results suggest that mitochondrial ATP synthetic capacity of the quadriceps muscle was intact but cardiac output to the leg muscles during exercise was insufficient to meet the muscular demand for oxygen. Therefore, improving cardiac output remains the main therapeutic target to improve exercise capacity in patients with a Fontan circulation

Resonant tunnelling features in the transport spectroscopy of quantum dots

We present a review of features due to resonant tunnelling in transport spectroscopy experiments on quantum dots and single donors. The review covers features attributable to intrinsic properties of the dot as well as extrinsic effects, with a focus on the most common operating conditions. We describe several phenomena that can lead to apparently identical signatures in a bias spectroscopy measurement, with the aim of providing experimental methods to distinguish between their different physical origins. The correct classification of the resonant tunnelling features is an essential requirement to understand the details of the confining potential or predict the performance of the dot for quantum information processing.Comment: 18 pages, 7 figures. Short review article submitted to Nanotechnology, special issue on 'Quantum Science and Technology at the Nanoscale