Operation of a silicon quantum processor unit cell above one kelvin.

Quantum computers are expected to outperform conventional computers in several important applications, from molecular simulation to search algorithms, once they can be scaled up to large numbers-typically millions-of quantum bits (qubits)1-3. For most solid-state qubit technologies-for example, those using superconducting circuits or semiconductor spins-scaling poses a considerable challenge because every additional qubit increases the heat generated, whereas the cooling power of dilution refrigerators is severely limited at their operating temperature (less than 100 millikelvin)4-6. Here we demonstrate the operation of a scalable silicon quantum processor unit cell comprising two qubits confined to quantum dots at about 1.5 kelvin. We achieve this by isolating the quantum dots from the electron reservoir, and then initializing and reading the qubits solely via tunnelling of electrons between the two quantum dots7-9. We coherently control the qubits using electrically driven spin resonance10,11 in isotopically enriched silicon12 28Si, attaining single-qubit gate fidelities of 98.6 per cent and a coherence time of 2 microseconds during 'hot' operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures13-16. Furthermore, we show that the unit cell can be operated at magnetic fields as low as 0.1 tesla, corresponding to a qubit control frequency of 3.5 gigahertz, where the qubit energy is well below the thermal energy. The unit cell constitutes the core building block of a full-scale silicon quantum computer and satisfies layout constraints required by error-correction architectures8,17. Our work indicates that a spin-based quantum computer could be operated at increased temperatures in a simple pumped 4He system (which provides cooling power orders of magnitude higher than that of dilution refrigerators), thus potentially enabling the integration of classical control electronics with the qubit array18,19.

Fidelity benchmarks for two-qubit gates in silicon.

Universal quantum computation will require qubit technology based on a scalable platform1, together with quantum error correction protocols that place strict limits on the maximum infidelities for one- and two-qubit gate operations2,3. Although various qubit systems have shown high fidelities at the one-qubit level4-10, the only solid-state qubits manufactured using standard lithographic techniques that have demonstrated two-qubit fidelities near the fault-tolerance threshold6 have been in superconductor systems. Silicon-based quantum dot qubits are also amenable to large-scale fabrication and can achieve high single-qubit gate fidelities (exceeding 99.9 per cent) using isotopically enriched silicon11,12. Two-qubit gates have now been demonstrated in a number of systems13-15, but as yet an accurate assessment of their fidelities using Clifford-based randomized benchmarking, which uses sequences of randomly chosen gates to measure the error, has not been achieved. Here, for qubits encoded on the electron spin states of gate-defined quantum dots, we demonstrate Bell state tomography with fidelities ranging from 80 to 89 per cent, and two-qubit randomized benchmarking with an average Clifford gate fidelity of 94.7 per cent and an average controlled-rotation fidelity of 98 per cent. These fidelities are found to be limited by the relatively long gate times used here compared with the decoherence times of the qubits. Silicon qubit designs employing fast gate operations with high Rabi frequencies16,17, together with advanced pulsing techniques18, should therefore enable much higher fidelities in the near future.

The Misinformation Susceptibility Test (MIST): A psychometrically validated measure of news veracity discernment.

Interest in the psychology of misinformation has exploded in recent years. Despite ample research, to date there is no validated framework to measure misinformation susceptibility. Therefore, we introduce Verification done, a nuanced interpretation schema and assessment tool that simultaneously considers Veracity discernment, and its distinct, measurable abilities (real/fake news detection), and biases (distrust/naïvité-negative/positive judgment bias). We then conduct three studies with seven independent samples (Ntotal = 8504) to show how to develop, validate, and apply the Misinformation Susceptibility Test (MIST). In Study 1 (N = 409) we use a neural network language model to generate items, and use three psychometric methods-factor analysis, item response theory, and exploratory graph analysis-to create the MIST-20 (20 items; completion time < 2 minutes), the MIST-16 (16 items; < 2 minutes), and the MIST-8 (8 items; < 1 minute). In Study 2 (N = 7674) we confirm the internal and predictive validity of the MIST in five national quota samples (US, UK), across 2 years, from three different sampling platforms-Respondi, CloudResearch, and Prolific. We also explore the MIST's nomological net and generate age-, region-, and country-specific norm tables. In Study 3 (N = 421) we demonstrate how the MIST-in conjunction with Verification done-can provide novel insights on existing psychological interventions, thereby advancing theory development. Finally, we outline the versatile implementations of the MIST as a screening tool, covariate, and intervention evaluation framework. As all methods are transparently reported and detailed, this work will allow other researchers to create similar scales or adapt them for any population of interest.

Combining ALS and UAV to derive the height of \textit{Araucaria angustifolia.

Quantitative data obtained from native forests is costly and time-consuming. Thus, alternative measurement methods need to be developed to provide reliable information, especially in Atlantic Rain Forests. In this study we evaluated the hypothesis that the combination of an Airborne Laser Scanner (ALS) and an Unmanned Aerial Vehicle (UAV) can provide accurate quantitative information on tree height, volume, and aboveground biomass of the Araucaria angustifolia species. The study was carried out in Atlantic Rain forest fragments in southern Brazil. We tested and evaluated 3 digital canopy height model (CHM) scenarios: 1) CHM derived from ALS models; 2) CHM derived from UAV models; and 3) CHM from a combined ALS digital terrain model and UAV digital surface model. The height value at each tree coordinate was extracted from the pixel in the three evaluated scenarios and compared with the field measured values. ALS and UAV+ALS obtained RMSE% of 6.38 and 12.82 for height estimates, while UAV was 49.91%. Volume and aboveground biomass predictions are more accurate by ALS and UAV+ALS, while the UAV produced biased estimates. Since the ALS is currently used, periodic monitoring can be carried out by a combination of active (ALS) and passive (UAV) sensors.

Acute Chagas Disease Manifesting as Orbital Cellulitis, Texas, USA.

We report a case of acute, vectorborne Chagas disease, acquired locally in central Texas, USA, manifesting as Romaña's sign, which was initially mistaken for orbital cellulitis. After the infection failed to respond to antibiotics, DNA-based next generation sequencing on plasma yielded high levels of Trypanasoma cruzi; results were confirmed by PCR.

A two-qubit logic gate in silicon.

Quantum computation requires qubits that can be coupled in a scalable manner, together with universal and high-fidelity one- and two-qubit logic gates. Many physical realizations of qubits exist, including single photons, trapped ions, superconducting circuits, single defects or atoms in diamond and silicon, and semiconductor quantum dots, with single-qubit fidelities that exceed the stringent thresholds required for fault-tolerant quantum computing. Despite this, high-fidelity two-qubit gates in the solid state that can be manufactured using standard lithographic techniques have so far been limited to superconducting qubits, owing to the difficulties of coupling qubits and dephasing in semiconductor systems. Here we present a two-qubit logic gate, which uses single spins in isotopically enriched silicon and is realized by performing single- and two-qubit operations in a quantum dot system using the exchange interaction, as envisaged in the Loss-DiVincenzo proposal. We realize CNOT gates via controlled-phase operations combined with single-qubit operations. Direct gate-voltage control provides single-qubit addressability, together with a switchable exchange interaction that is used in the two-qubit controlled-phase gate. By independently reading out both qubits, we measure clear anticorrelations in the two-spin probabilities of the CNOT gate.

Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial.

BACKGROUND: Phase 1 studies have shown potential benefit of gene replacement in RPE65-mediated inherited retinal dystrophy. This phase 3 study assessed the efficacy and safety of voretigene neparvovec in participants whose inherited retinal dystrophy would otherwise progress to complete blindness. METHODS: In this open-label, randomised, controlled phase 3 trial done at two sites in the USA, individuals aged 3 years or older with, in each eye, best corrected visual acuity of 20/60 or worse, or visual field less than 20 degrees in any meridian, or both, with confirmed genetic diagnosis of biallelic RPE65 mutations, sufficient viable retina, and ability to perform standardised multi-luminance mobility testing (MLMT) within the luminance range evaluated, were eligible. Participants were randomly assigned (2:1) to intervention or control using a permuted block design, stratified by age (<10 years and ≥10 years) and baseline mobility testing passing level (pass at ≥125 lux vs <125 lux). Graders assessing primary outcome were masked to treatment group. Intervention was bilateral, subretinal injection of 1·5 × 1011 vector genomes of voretigene neparvovec in 0·3 mL total volume. The primary efficacy endpoint was 1-year change in MLMT performance, measuring functional vision at specified light levels. The intention-to-treat (ITT) and modified ITT populations were included in primary and safety analyses. This trial is registered with ClinicalTrials.gov, number NCT00999609, and enrolment is complete. FINDINGS: Between Nov 15, 2012, and Nov 21, 2013, 31 individuals were enrolled and randomly assigned to intervention (n=21) or control (n=10). One participant from each group withdrew after consent, before intervention, leaving an mITT population of 20 intervention and nine control participants. At 1 year, mean bilateral MLMT change score was 1·8 (SD 1·1) light levels in the intervention group versus 0·2 (1·0) in the control group (difference of 1·6, 95% CI 0·72-2·41, p=0·0013). 13 (65%) of 20 intervention participants, but no control participants, passed MLMT at the lowest luminance level tested (1 lux), demonstrating maximum possible improvement. No product-related serious adverse events or deleterious immune responses occurred. Two intervention participants, one with a pre-existing complex seizure disorder and another who experienced oral surgery complications, had serious adverse events unrelated to study participation. Most ocular events were mild in severity. INTERPRETATION: Voretigene neparvovec gene replacement improved functional vision in RPE65-mediated inherited retinal dystrophy previously medically untreatable. FUNDING: Spark Therapeutics.

Prevalence and Predictors of Uncircumcised, Kenyan Men's Desire for Circumcision for Their Infant Sons.

Men are key decision makers for their son's circumcision, so understanding their beliefs is important for the uptake of early infant male circumcision in countries in sub-Saharan Africa that have high HIV prevalence. We analyzed men's preferences for circumcising their sons using data from a population-representative survey of 1501 uncircumcised men aged 25-49 years in western Kenya. Most men (59%) reported they would "definitely" want their son circumcised if a son was born to them within the next year. However, only 25% intended to become circumcised themselves. In multivariable Poisson regression models to estimate prevalence ratios, key predictors of the desire to circumcise their sons included knowledge that circumcision reduces HIV acquisition, having a supportive partner, discussing circumcision with the partner, altruism, and intention to be circumcised himself. Focusing on partner dynamics may have the greatest capacity to increase demand since 55% had not talked to their partner about circumcision.

Challenges, successes and patterns of enrolment in the INSIGHT Strategic Timing of AntiRetroviral Treatment (START) trial.

OBJECTIVES: The aim of this report is to describe the challenges, successes and patterns of enrolment in the Strategic Timing of AntiRetroviral Treatment (START) study. METHODS: START is a collaboration of many partners with central coordination provided by the protocol team, the statistical and data management centre (SDMC), the International Network for Strategic Initiatives in Global HIV Trials (INSIGHT) network leadership, international coordinating centres and site coordinating centres. The SDMC prepared reports on study accrual, baseline characteristics and site performance that allowed monitoring of enrolment and data quality and helped to ensure the successful enrolment of this large international trial. We describe the pattern of enrolment and challenges faced during the enrolment period of the trial. RESULTS: An initial pilot phase began in April 2009 and established feasibility of accrual at 101 sites. In August 2010, funding approval for an expanded definitive phase led to the successful accrual of 4688 participants from 215 sites in 35 countries by December 2013. Challenges to accrual included regulatory delays (e.g. national/local ethics approval and drug importation approval) and logistical obstacles (e.g. execution of contracts with pharmaceutical companies, setting up of a central drug repository and translation of participant materials). The personal engagement of investigators, strong central study coordination, and frequent and transparent communication with site investigators, community members and participants were key contributing factors to this success. CONCLUSIONS: Accrual into START was completed in a timely fashion despite multiple challenges. This success was attributable to the efforts of site investigators committed to maintaining study equipoise, transparent and responsive study coordination, and community involvement in problem-solving.

Oral ß-lactams vs fluoroquinolones and trimethoprim/sulfamethoxazole for step-down therapy for Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae bacteremia.

PURPOSE: To compare rates of treatment failure for patients with bloodstream infections (BSIs) due to Escherichia coli, Klebsiella pneumoniae, or Proteus mirabilis who received oral step-down antibiotic therapy with either a fluoroquinolone (FQ) or trimethoprim/sulfamethoxazole (SXT) to rates for those who received an oral ß-lactam (BL). METHODS: This retrospective, multicenter, cohort study included 397 unique adult hospitalized patients with a BSI due to E. coli, K. pneumoniae, or P. mirabilis at 6 hospitals in central Texas between July 11, 2016, and July 11, 2018. The primary outcome was a composite of treatment failure comprising 30-day readmission due to recurrence, 30-day all-cause mortality, and change in oral antibiotic. Secondary outcomes included 90-day development of Clostridioides difficile infection, 90-day colonization with a multidrug-resistant organism, 90-day all-cause readmission, hospital length of stay, and the individual components of the primary outcome. RESULTS: Of the 397 patients included, 200 received oral step-down therapy with a BL while 197 received an FQ or SXT. Most patients had an infection due to E. coli (82.8%) and a urinary source of infection (85%). Median total duration of therapy was 14 days in both groups. No difference in treatment failure was identified between the groups treated with a BL and FQ/SXT (7% vs 5.8%, P = 0.561). Median hospital length of stay was the only secondary endpoint in which there was an observed difference (6 vs 5 days, P = 0.04). CONCLUSION: We observed no difference in treatment failure rates for patients receiving an oral BL compared to an oral FQ or SXT for step-down therapy of BSIs due to E. coli, K. pneumoniae, and P. mirabilis.

Rapid screening for the detection of HLA-B57 and HLA-B58 in prevention of drug hypersensitivity.

HLA-B57 and HLA-B58 are major histocompatibility class (MHC)-I allotypes that are potentially predictive of important clinical immune phenotypes. HLA-B*5701 is strongly associated with hypersensitivity to the HIV drug abacavir, liver toxicity from the antibiotic flucloxacillin and is a marker for slow progression of HIV AIDS. HLA-B*5801 is associated with hypersensitivity to allopurinol used to treat hyperuricaemia and recurrent gout. Here we describe a monoclonal antibody (mAb) specific for HLA-B57 and HLA-B58 that provides an inexpensive and sensitive screen for these MHC-I allotypes. The usefulness of HLA-B57 screening for prediction of abacavir hypersensitivity was shown in three independent laboratories, including confirmation of the mAb sensitivity and specificity in a cohort of patients enrolled in the PREDICT-1 trial. Our data show that patients who test negative by mAb screening comprise 90%-95% of all individuals in most human populations and require no further human leukocyte antigen (HLA) typing. Patients who test positive by mAb screening should proceed to high-resolution typing to ascertain the presence of HLA-B*5701 or HLA-B*5801. Hence, mAb screening provides a low-cost alternative to high-resolution typing of all patients and lends itself to point-of-care diagnostics and rapid ascertainment of low-risk patients who can begin immediate therapy with abacavir, flucloxacillin or allopurinol.

Coherent spin qubit transport in silicon.

A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.

Genetic, epigenetic, and environmental factors controlling oxytocin receptor gene expression.

BACKGROUND: The neuropeptide oxytocin regulates mammalian social behavior. Disruptions in oxytocin signaling are a feature of many psychopathologies. One commonly studied biomarker for oxytocin involvement in psychiatric diseases is DNA methylation at the oxytocin receptor gene (OXTR). Such studies focus on DNA methylation in two regions of OXTR, exon 3 and a region termed MT2 which overlaps exon 1 and intron 1. However, the relative contribution of exon 3 and MT2 in regulating OXTR gene expression in the brain is currently unknown. RESULTS: Here, we use the prairie vole as a translational animal model to investigate genetic, epigenetic, and environmental factors affecting Oxtr gene expression in a region of the brain that has been shown to drive Oxtr related behavior in the vole, the nucleus accumbens. We show that the genetic structure of Oxtr in prairie voles resembles human OXTR. We then studied the effects of early life experience on DNA methylation in two regions of a CpG island surrounding the Oxtr promoter: MT2 and exon 3. We show that early nurture in the form of parental care results in DNA hypomethylation of Oxtr in both MT2 and exon 3, but only DNA methylation in MT2 is associated with Oxtr gene expression. Network analyses indicate that CpG sites in the 3' portion of MT2 are most highly associated with Oxtr gene expression. We also identify two novel SNPs in exon 3 of Oxtr in prairie voles and a novel alternative transcript originating from the third intron of the gene. Expression of the novel alternative transcript is associated with genotype at SNP KLW2. CONCLUSIONS: These results identify putative regulatory features of Oxtr in prairie voles which inform future studies examining OXTR in human social behaviors and disorders. These studies indicate that in prairie voles, DNA methylation in MT2, particularly in the 3' portion, is more predictive of Oxtr gene expression than DNA methylation in exon 3. Similarly, in human temporal cortex, we find that DNA methylation in the 3' portion of MT2 is associated with OXTR expression. Together, these results suggest that among the CpG sites studied, DNA methylation of MT2 may be the most reliable indicator of OXTR gene expression. We also identify novel features of prairie vole Oxtr, including SNPs and an alternative transcript, which further develop the prairie vole as a translational model for studies of OXTR.

Solid phase HLA antibody detection technology--challenges in interpretation.

The introduction into routine diagnostic laboratories of solid phase assays for human leukocyte antigen (HLA) antibody detection has resulted in the application of new laboratory matching algorithms in clinical organ transplantation which have improved pre-transplant detection of immunization, in turn resulting in avoidance of rejection in many cases which until their introduction would not have been possible using the historical complement dependent serological techniques. There have been two generations of solid phase assays introduced into routine practice, namely, the enzyme-linked immunosorbent assay (ELISA) technique and the use of fluorescent beads with HLA molecules bound to their surface which can either be used in conventional flow cytometry or in conjunction with Luminex instrumentation, the latter having become the most popular approach. The use of the fluorescent bead techniques has raised interesting questions both with respect to technical performance and the interpretation of the results obtained. The advantages of bead technology for HLA antibody determination and the technical issues requiring resolution are the subject of this review.

Coherent spin control of s-, p-, d- and f-electrons in a silicon quantum dot.

Once the periodic properties of elements were unveiled, chemical behaviour could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in semiconductor materials disrupt this analogy, so real devices seldom display a systematic many-electron arrangement. We demonstrate here an electrostatically confined quantum dot that reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. Various fillings containing a single valence electron-namely 1, 5, 13 and 25 electrons-are found to be potential qubits. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR), leading to faster Rabi rotations and higher fidelity single qubit gates at higher shell states. We investigate the impact of orbital excitations on single qubits as a function of the dot deformation and exploit it for faster qubit control.

Is Small Still Beautiful for the Strengths and Difficulties Questionnaire? Novel Findings Using Exploratory Structural Equation Modeling.

During the present decade a large body of research has employed confirmatory factor analysis (CFA) to evaluate the factor structure of the Strengths and Difficulties Questionnaire (SDQ) across multiple languages and cultures. However, because CFA can produce strongly biased estimations when the population cross-loadings differ meaningfully from zero, it may not be the most appropriate framework to model the SDQ responses. With this in mind, the current study sought to assess the factorial structure of the SDQ using the more flexible exploratory structural equation modeling approach. Using a large-scale Spanish sample composed of 67,253 youths aged between 10 and 18 years (M = 14.16, SD = 1.07), the results showed that CFA provided a severely biased and overly optimistic assessment of the underlying structure of the SDQ. In contrast, exploratory structural equation modeling revealed a generally weak factorial structure, including questionable indicators with large cross-loadings, multiple error correlations, and significant wording variance. A subsequent Monte Carlo study showed that sample sizes greater than 4,000 would be needed to adequately recover the SDQ loading structure. The findings from this study prevent recommending the SDQ as a screening tool and suggest caution when interpreting previous results in the literature based on CFA modeling.

Evolution of HIV-1 drug resistance after virological failure of first-line antiretroviral therapy in Lusaka, Zambia.

BACKGROUND: HIV viral load (VL) and resistance testing are limited in sub-Saharan Africa, so individuals may have prolonged time on failing first-line antiretroviral therapy (ART). Our objective was to describe the evolution of drug resistance mutations among adults failing first-line ART in Zambia. METHODS: We analysed data from a trial of VL monitoring in Lusaka, Zambia. From 2006 to 2011, 12 randomized sites provided either routine VL monitoring (intervention) or discretionary (control) after ART initiation. Samples were collected prospectively following the same schedule in each arm but analysed retrospectively in the control group. For those with virological failure (VF; >400 copies/ml), HIV genotyping was performed retrospectively on baseline (BL) and on all subsequent specimens until censored due to study completion, withdrawal or death. RESULTS: Of 1,973 enrollees, 165 (8.4%) developed VF. 464 genotype results were available including 132 (80%) at BL, 116 (70%) at VF and 125 (76%) had at least one result between VF and censoring. Major nucleoside reverse transcriptase inhibitor (NRTI) or non-nucleoside reverse transcriptase inhibitor (NNRTI) mutations increased from 26% (BL) to 82% (VF) to 89% at last genotype (LG). M184 mutations increased from 2% to 59% to 71%; K65R from 2% to 11% to 13%; 2 or more thymidine analogue mutations from 1% to 3% to 12%. Among those on a failing tenofovir disoproxil fumarate (TDF)-based regimen, TDF resistance increased from 42% to 58%. CONCLUSIONS: We found substantial resistance to NRTIs and NNRTIs at VF with incremental increases after VF while still on a failing first-line ART; this resistance may compromise attainment of the UNAIDS 90-90-90 goals.

Exploratory Graph Analysis of the Multidimensional Schizotypy Scale.

The present study examined the dimensional structure underlying the Multidimensional Schizotypy Scale (MSS) and its brief version (MSS-B). We used Exploratory Graph Analysis (EGA) to evaluate their dimensional structure in two large, independent samples (n = 6265 and n = 1000). We then used Confirmatory Factor Analysis (CFA) to compare the fit of the theoretical dimensions with the EGA dimensions. For the MSS, EGA identified four dimensions: positive schizotypy, two dimensions of negative schizotypy (affective and social anhedonia), and disorganized schizotypy. For the MSS-B, EGA identified three dimensions, which corresponded to the theorized positive, negative, and disorganized dimensions. Based on the MSS's EGA dimensions, we also estimated a four-factor model for the MSS-B. The CFA comparison found that the four-factor model fit significantly better than the theoretical three-factor model for both the MSS and MSS-B, providing support for the theoretical model and offering a more nuanced interpretation of the negative schizotypy factor. In addition, EGA also revealed that the positive and negative schizotypy dimensions of the MSS and MSS-B might be mediated by the disorganized dimension. Our findings offer new implications for future research on the MSS and MSS-B dimensions that may provide differential associations with interview and questionnaire measures.

Single-spin qubits in isotopically enriched silicon at low magnetic field.

Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling. This requires demanding microwave engineering for coherent spin resonance control, which limits the prospects for large scale multi-qubit systems. Alternatively, singlet-triplet readout enables high-fidelity spin-state measurements in much lower magnetic fields, without the need for reservoirs. Here, we demonstrate low-field operation of metal-oxide-silicon quantum dot qubits by combining coherent single-spin control with high-fidelity, single-shot, Pauli-spin-blockade-based ST readout. We discover that the qubits decohere faster at low magnetic fields with [Formula: see text] µs and [Formula: see text] µs at 150 mT. Their coherence is limited by spin flips of residual 29Si nuclei in the isotopically enriched 28Si host material, which occur more frequently at lower fields. Our finding indicates that new trade-offs will be required to ensure the frequency stabilization of spin qubits, and highlights the importance of isotopic enrichment of device substrates for the realization of a scalable silicon-based quantum processor.