Operating semiconductor quantum processors with hopping spins.

Qubits that can be efficiently controlled are essential for the development of scalable quantum hardware. Although resonant control is used to execute high-fidelity quantum gates, the scalability is challenged by the integration of high-frequency oscillating signals, qubit cross-talk, and heating. Here, we show that by engineering the hopping of spins between quantum dots with a site-dependent spin quantization axis, quantum control can be established with discrete signals.

Coherent spin qubit shuttling through germanium quantum dots.

Quantum links can interconnect qubit registers and are therefore essential in networked quantum computing. Semiconductor quantum dot qubits have seen significant progress in the high-fidelity operation of small qubit registers but establishing a compelling quantum link remains a challenge. Here, we show that a spin qubit can be shuttled through multiple quantum dots while preserving its quantum information.

Bichromatic Rabi Control of Semiconductor Qubits.

Electrically driven spin resonance is a powerful technique for controlling semiconductor spin qubits. However, it faces challenges in qubit addressability and off-resonance driving in larger systems. We demonstrate coherent bichromatic Rabi control of quantum dot hole spin qubits, offering a spatially selective approach for large qubit arrays.

Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold.

Practical Quantum computing hinges on the ability to control large numbers of qubits with high fidelity. Quantum dots define a promising platform due to their compatibility with semiconductor manufacturing. Moreover, high-fidelity operations above 99.

Universal control of a six-qubit quantum processor in silicon.

Future quantum computers capable of solving relevant problems will require a large number of qubits that can be operated reliably. However, the requirements of having a large qubit count and operating with high fidelity are typically conflicting. Spins in semiconductor quantum dots show long-term promise but demonstrations so far use between one and four qubits and typically optimize the fidelity of either single- or two-qubit operations, or initialization and readout.

A four-qubit germanium quantum processor.

The prospect of building quantum circuits using advanced semiconductor manufacturing makes quantum dots an attractive platform for quantum information processing. Extensive studies of various materials have led to demonstrations of two-qubit logic in gallium arsenide, silicon and germanium. However, interconnecting larger numbers of qubits in semiconductor devices has remained a challenge.

Spin Relaxation Benchmarks and Individual Qubit Addressability for Holes in Quantum Dots.

We investigate hole spin relaxation in the single- and multihole regime in a 2 × 2 germanium quantum dot array. We find spin relaxation times as high as 32 and 1.2 ms for quantum dots with single- and five-hole occupations, respectively, setting benchmarks for spin relaxation times for hole quantum dots.

A single-hole spin qubit.

Qubits based on quantum dots have excellent prospects for scalable quantum technology due to their compatibility with standard semiconductor manufacturing. While early research focused on the simpler electron system, recent demonstrations using multi-hole quantum dots illustrated the favourable properties holes can offer for fast and scalable quantum control. Here, we establish a single-hole spin qubit in germanium and demonstrate the integration of single-shot readout and quantum control.

Universal quantum logic in hot silicon qubits.

Quantum computation requires many qubits that can be coherently controlled and coupled to each other. Qubits that are defined using lithographic techniques have been suggested to enable the development of scalable quantum systems because they can be implemented using semiconductor fabrication technology. However, leading solid-state approaches function only at temperatures below 100 millikelvin, where cooling power is extremely limited, and this severely affects the prospects of practical quantum computation.

Tunable Coupling and Isolation of Single Electrons in Silicon Metal-Oxide-Semiconductor Quantum Dots.

Extremely long coherence times, excellent single-qubit gate fidelities, and two-qubit logic have been demonstrated with silicon metal-oxide-semiconductor spin qubits, making it one of the leading platforms for quantum information processing. Despite this, a long-standing challenge in this system has been the demonstration of tunable tunnel coupling between single electrons. Here we overcome this hurdle with gate-defined quantum dots and show couplings that can be tuned on and off for quantum operations.

Metabolites in ventricular cerebrospinal fluid detected by proton magnetic resonance spectroscopic imaging.

Normally, ventricular cerebrospinal fluid (CSF) contains low levels of all metabolite signals on proton magnetic resonance spectroscopic imaging (MRSI). We present here three cases (two with seizure disorders, one with a central nervous system lymphoma) who presented with unusually elevated CSF signals on MRSI. Based on chemical shifts and in vitro studies (in one case), the signals were assigned to propan-1,2-diol (PD), acetone, and lactate, respectively.

Diffusion tensor imaging of periventricular leukomalacia shows affected sensory cortex white matter pathways.

The authors used diffusion-tensor imaging to examine central white matter pathways in two children with spastic quadriplegic cerebral palsy. Corticospinal tracts projecting from cortex to brainstem resembled controls. In contrast, posterior regions of the corpus callosum, internal capsule, and corona radiata were markedly reduced, primarily in white matter fibers connected to sensory cortex.

Acute and late radiotherapy toxicity in patients with inflammatory bowel disease.

Purpose: To evaluate the incidence of gastrointestinal complications in patients with inflammatory bowel disease (IBD) receiving radiotherapy (RT) and to identify possibly avoidable factors associated with these complications.

Methods And Materials: Twenty-four patients were identified and their records reviewed; all had a history of IBD before receiving RT to fields encompassing some portion of the gastrointestinal tract (Crohn's disease) or to the abdomen or pelvis (ulcerative colitis or IBD not otherwise specified).

Results: Five of 24 patients (21%) experienced Grade > or =3 acute gastrointestinal toxicity; all 5 received concurrent chemotherapy.

Age-dependent effects of trihexyphenidyl in extrapyramidal cerebral palsy.

Trihexyphenidyl (Artane) is a centrally active muscarinic antagonist commonly used to treat patients with generalized dystonia. In a retrospective survey of 22 consecutive children with extrapyramidal cerebral palsy, we evaluated trihexyphenidyl on upper extremity and lower extremity function, expressive language, and drooling. Functional changes were assessed using a parental questionnaire (rating scale 1-5: from 1 = little or no change to 5 = tremendous change, with scores in either a positive or negative direction).

Determination of radium-226 in environmental and personal monitoring samples.

Radium-226 is a member of the Uranium-238 natural decay series and is the most hazardous radionuclide released to the environment from uranium mining and milling. Due to its long half-life (1600 years) and radiological effects it is one of the most important isotopes to be determined among the naturally occurring nuclides in environmental samples. It is also among the most toxic long-lived alpha-emitters present in environmental samples, as well as one of the most widespread.

1H NMR as a non-invasive probe of amniotic fluid in insulin dependent diabetes mellitus.

Ten amniotic fluid samples obtained from third trimester pregnant women suffering from insulin dependant diabetes mellitus were analysed by 1H-NMR and compared to ten samples from a group of normal volunteers. A subset of the metabolites identified; valine, lactate, alanine, acetate, citrate and glucose were quantitated using standard addition methods. Apart from valine and citrate, a general diminution in the concentration of each of these species was found, especially glucose, in the diabetic group.