Nickel as a co-catalyst for photocatalytic hydrogen evolution on graphitic-carbon nitride (sg-CN): what is the nature of the active species?

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The nature of a nickel-based co-catalyst deposited on a sol-gel prepared porous graphitic-carbon nitride (sg-CN), for photocatalytic H-2 production from water, has been investigated. The formation of the active catalytic species, charge separation and recombination of the photogenerated electrons and holes during photochemical H-2 evolution has been determined for the first time using in situ EPR spectroscopy.DFG, EXC 314, Unifying Concepts in CatalysisBMBF, 03IS2071D, Light2Hydroge

Protective intraoperative ventilation with higher versus lower levels of positive end-expiratory pressure in obese patients (PROBESE): study protocol for a randomized controlled trial

Background: Postoperative pulmonary complications (PPCs) increase the morbidity and mortality of surgery in obese patients. High levels of positive end-expiratory pressure (PEEP) with lung recruitment maneuvers may improve intraoperative respiratory function, but they can also compromise hemodynamics, and the effects on PPCs are uncertain. We hypothesized that intraoperative mechanical ventilation using high PEEP with periodic recruitment maneuvers, as compared with low PEEP without recruitment maneuvers, prevents PPCs in obese patients. Methods/design The PRotective Ventilation with Higher versus Lower PEEP during General Anesthesia for Surgery in OBESE Patients (PROBESE) study is a multicenter, two-arm, international randomized controlled trial. In total, 2013 obese patients with body mass index ≥35 kg/m2 scheduled for at least 2 h of surgery under general anesthesia and at intermediate to high risk for PPCs will be included. Patients are ventilated intraoperatively with a low tidal volume of 7 ml/kg (predicted body weight) and randomly assigned to PEEP of 12 cmH2O with lung recruitment maneuvers (high PEEP) or PEEP of 4 cmH2O without recruitment maneuvers (low PEEP). The occurrence of PPCs will be recorded as collapsed composite of single adverse pulmonary events and represents the primary endpoint. Discussion To our knowledge, the PROBESE trial is the first multicenter, international randomized controlled trial to compare the effects of two different levels of intraoperative PEEP during protective low tidal volume ventilation on PPCs in obese patients. The results of the PROBESE trial will support anesthesiologists in their decision to choose a certain PEEP level during general anesthesia for surgery in obese patients in an attempt to prevent PPCs. Trial registration ClinicalTrials.gov identifier: NCT02148692. Registered on 23 May 2014; last updated 7 June 2016. Electronic supplementary material The online version of this article (doi:10.1186/s13063-017-1929-0) contains supplementary material, which is available to authorized users

Relaxation and decoherence of a 28Si/SiGe spin qubit with large valley splitting

Electron spin qubits in gate defined Si/SiGe quantum dots have become one of the most promising platforms for spin based quantum computation. Single-qubit gate fidelities higher than the error correcting threshold and two-qubit gates have been demonstrated. Applying industrial fabrication processes and integrating conventional silicon electronics opens up the perspective of a highly scalable and dense quantum computing architecture. However, quantum dots in Si/SiGe heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. In this work we demonstrate a robust and large valley splitting exceeding 200$\,\mu$eV in a gate-defined quantum dot, hosted in molecular-beam epitaxy-grown $^{28}$Si/SiGe with a residual $^{29}$Si contribution of only 60 ppm. We model the spin relaxation mechanisms and observe static spin relaxation times $T_1>1$ s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, $T_1$ is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking. The large valley splittings with reproducible stability represent a step forward for the realisation of multi-qubit devices and qubits at elevated temperature. We demonstrate single-shot spin read-out and electric dipole spin resonance control with a single domain nanomagnet. The maximal Rabi-frequency of 1 MHz is limited by unintentional electron exchange with the reservoir. We measure a dephasing time of $T_2^*= (19.14\pm 0.40)\,\mu\text{s}$ for a measurement time of four minutes and discuss possible measurements to discriminate the underlying dephasing mechanisms in this device. The measured record spin echo time of $T_2^\text{echo} =(131\pm4)\,\mu\text{s}$ is not effected by the voltage bias and current of the near-by charge sensor. Quantum error correction requires millions of physical qubits and therefore a scalable quantum computer architecture. To solve signal-line bandwidth and fan-out problems, microwave sources required for qubit manipulation might be embedded close to the qubit chip. In this context, we perform the first low temperature measurements of a 130 nm BiCMOS based SiGe voltage controlled oscillator at cryogenic temperature that maintains its full functionality from 300 K to 4 K. We determined the frequency and power dependence on temperature and magnetic field up to 5 T and measured the temperature influence on its noise performance

30 GHz-voltage controlled oscillator operating at 4 K

Solid-state qubit manipulation and read-out fidelities are reaching fault-tolerance, but quantum error correction requires millions of physical qubits and therefore a scalable quantum computer architecture. To solve signal-line bandwidth and fan-out problems, microwave sources required for qubit manipulation might be embedded close to the qubit chip, typically operating at temperatures below 4 K. Here, we perform the first low temperature measurements of a 130 nm BiCMOS based SiGe voltage controlled oscillator at cryogenic temperature. We determined the frequency and output power dependence on temperature and magnetic field up to 5 T and measured the temperature influence on its noise performance. The device maintains its full functionality from 300 K to 4 K. The carrier frequency at 4 K increases by 3% with respect to the carrier frequency at 300 K, and the output power at 4 K increases by 10 dB relative to the output power at 300 K. The frequency tuning range of approximately 20% remains unchanged between 300 K and 4 K. In an in-plane magnetic field of 5 T, the carrier frequency shifts by only 0.02% compared to the frequency at zero magnetic field

Robust and fast post-processing of single-shot spin qubit detection events with a neural network

Establishing low-error and fast detection methods for qubit readout is crucial for efficient quantum error correction. Here, we test neural networks to classify a collection of single-shot spin detection events, which are the readout signal of our qubit measurements. This readout signal contains a stochastic peak, for which a Bayesian inference filter including Gaussian noise is theoretically optimal. Hence, we benchmark our neural networks trained by various strategies versus this latter algorithm. Training of the network with 10$^{6}$ experimentally recorded single-shot readout traces does not improve the post-processing performance. A network trained by synthetically generated measurement traces performs similar in terms of the detection error and the post-processing speed compared to the Bayesian inference filter. This neural network turns out to be more robust to fluctuations in the signal offset, length and delay as well as in the signal-to-noise ratio. Notably, we find an increase of 7 % in the visibility of the Rabi-oscillation when we employ a network trained by synthetic readout traces combined with measured signal noise of our setup. Our contribution thus represents an example of the beneficial role which software and hardware implementation of neural networks may play in scalable spin qubit processor architectures

Large, Tunable Valley Splitting and Single-Spin Relaxation Mechanisms in a Si / Si x Ge 1 − x Quantum Dot

Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in Si/SixGe1−x heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 μeV in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown 68Si/SixGe1−x. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times T1>1 s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, T1 is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking

Author Correction: Low-frequency spin qubit energy splitting noise in highly purified 28Si/SiGe (npj Quantum Information, (2020), 6, 1, (40), 10.1038/s41534-020-0276-2)

The original version of this Article omitted the following from the Acknowledgements: “This work has also been funded by the National Science Centre, Poland under QuantERA program, Grant No. 2017/25/Z/ST3/03044.” This has now been corrected in both the PDF and HTML versions of the Article. © 2020, The Author(s)