An integrated framework of coastal flood modelling under the failures of sea dikes: a case study in Shanghai

Climate change leads to sea level rise worldwide, as well as increases in the intensity and frequency of tropical cyclones (TCs). Storm surge induced by TC’s, together with spring tides, threatens to cause failure of flood defenses, resulting in massive flooding in low-lying coastal areas. However, limited research has been done on the...

Spatial noise correlations in a Si/SiGe two-qubit device from Bell state coherences

We study spatial noise correlations in a Si/SiGe two-qubit device with integrated micromagnets. Our method relies on the concept of decoherence-free subspaces, whereby we measure the coherence time for two different Bell states, designed to be sensitive only to either correlated or anticorrelated noise, respectively. From these measurements...

Repetitive Quantum Nondemolition Measurement and Soft Decoding of a Silicon Spin Qubit

Quantum error correction is of crucial importance for fault-tolerant quantum computers. As an essential step toward the implementation of quantum error-correcting codes, quantum nondemolition measurements are needed to efficiently detect the state of a logical qubit without destroying it. Here we implement quantum nondemolition measurements...

Benchmarking Gate Fidelities in a Si/SiGe Two-Qubit Device

We report the first complete characterization of single-qubit and two-qubit gate fidelities in silicon-based spin qubits, including cross talk and error correlations between the two qubits. To do so, we use a combination of standard randomized benchmarking and a recently introduced method called character randomized benchmarking, which allows...

Stealth Technologies to Reduce the Impact of Wind Turbines on Radar Systems

QinetiQ has investigated the topic of wind farm radar interference since for over 15 years, undertaking research activities and providing consultancy services. Principles of radar cross-section (RCS) reduction using stealth technologies are discussed. The strengths and weaknesses are considered in the context of other mitigation approaches. The...

The critical role of substrate disorder in valley splitting in Si quantum wells

Atomic-scale disorder at the top interface of a Si quantum well is known to suppress valley splitting. Such disorder may be inherited from the underlying substrate and relaxed buffer growth, but can also arise at the top quantum well interface due to the random SiGe alloy. Here, we perform activation energy (transport) measurements in the...

A programmable two-qubit quantum processor in silicon

Now that it is possible to achieve measurement and control fidelities for individual quantum bits (qubits) above the threshold for fault tolerance, attention is moving towards the difficult task of scaling up the number of physical qubits to the large numbers that are needed for fault-tolerant quantum computing. In this context, quantum-dot...

Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet

The gate fidelity and the coherence time of a quantum bit (qubit) are important benchmarks for quantum computation. We construct a qubit using a single electron spin in an Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of ∼99% using...

Second-Harmonic Coherent Driving of a Spin Qubit in a Si/SiGe Quantum Dot

We demonstrate coherent driving of a single electron spin using second-harmonic excitation in a Si/SiGe quantum dot. Our estimates suggest that the anharmonic dot confining potential combined with a gradient in the transverse magnetic field dominates the second-harmonic response. As expected, the Rabi frequency depends quadratically on the...

Single-Shot Readout of Singlet-Triplet Qubit States in a Si/SiGe Double Quantum Dot

The spin singlet and triplet states of a two-electron double quantum dot can be used to form a logical qubit that combines fast manipulation and a spin readout mechanism. We demonstrate single-shot readout of the two-electron states of a Si/SiGe double quantum dot using a quantum-point-contact charge sensor and spin-to-charge conversion. From...

Single-Shot Readout of Singlet-Triplet Qubit States in a Si/SiGe Double Quantum Dot (abstract)

Single-Shot Measurement of Triplet-Singlet Relaxation in a Si/SiGe Double Quantum Dot

We investigate the lifetime of two-electron spin states in a few-electron Si/SiGe double dot. At the transition between the (1,1) and (0,2) charge occupations, Pauli spin blockade provides a readout mechanism for the spin state. We use the statistics of repeated single-shot measurements to extract the lifetimes of multiple states simultaneously....