A silicon singlet-triplet qubit driven by spin-valley coupling.

Spin-orbit effects, inherent to electrons confined in quantum dots at a silicon heterointerface, provide a means to control electron spin qubits without the added complexity of on-chip, nanofabricated micromagnets or nearby coplanar striplines. Here, we demonstrate a singlet-triplet qubit operating mode that can drive qubit evolution at frequencies in excess of 200 MHz. This approach offers a means to electrically turn on and off fast control, while providing high logic gate orthogonality and long qubit dephasing times. We utilize this operational mode for dynamical decoupling experiments to probe the charge noise power spectrum in a silicon metal-oxide-semiconductor double quantum dot. In addition, we assess qubit frequency drift over longer timescales to capture low-frequency noise. We present the charge noise power spectral density up to 3 MHz, which exhibits a 1/fα dependence consistent with α ~ 0.7, over 9 orders of magnitude in noise frequency.

Spin-orbit Interactions for Singlet-Triplet Qubits in Silicon.

Spin-orbit coupling is relatively weak for electrons in bulk silicon, but enhanced interactions are reported in nanostructures such as the quantum dots used for spin qubits. These interactions have been attributed to various dissimilar interface effects, including disorder or broken crystal symmetries. In this Letter, we use a double-quantum-dot qubit to probe these interactions by comparing the spins of separated singlet-triplet electron pairs. We observe both intravalley and intervalley mechanisms, each dominant for [110] and [100] magnetic field orientations, respectively, that are consistent with a broken crystal symmetry model. We also observe a third spin-flip mechanism caused by tunneling between the quantum dots. This improved understanding is important for qubit uniformity, spin control and decoherence, and two-qubit gates.

Weak anti-localization of two-dimensional holes in germanium beyond the diffusive regime.

Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than ∼6 × 1011 cm-2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.

A silicon metal-oxide-semiconductor electron spin-orbit qubit.

The silicon metal-oxide-semiconductor (MOS) material system is a technologically important implementation of spin-based quantum information processing. However, the MOS interface is imperfect leading to concerns about 1/f trap noise and variability in the electron g-factor due to spin-orbit (SO) effects. Here we advantageously use interface-SO coupling for a critical control axis in a double-quantum-dot singlet-triplet qubit. The magnetic field-orientation dependence of the g-factors is consistent with Rashba and Dresselhaus interface-SO contributions. The resulting all-electrical, two-axis control is also used to probe the MOS interface noise. The measured inhomogeneous dephasing time, [Formula: see text], of 1.6 µs is consistent with 99.95% 28Si enrichment. Furthermore, when tuned to be sensitive to exchange fluctuations, a quasi-static charge noise detuning variance of 2 µeV is observed, competitive with low-noise reports in other semiconductor qubits. This work, therefore, demonstrates that the MOS interface inherently provides properties for two-axis qubit control, while not increasing noise relative to other material choices.

Breast cancer survivor's perspectives on the role different providers play in follow-up care.

IMPORTANCE: Significant variation in the number and types of oncologists that provide breast cancer follow-up exists. However, there is limited understanding regarding breast cancer survivors' preferences for who provides their follow-up. Our objective was to explore breast cancer survivors' perspectives on the goals of breast cancer follow-up, the preferred role for primary care providers, and the perceived roles of different types of oncologists during follow-up. METHODS: A convenience sample of stage 0-III breast cancer survivors was identified and in-depth one-on-one interviews conducted. Data were analyzed using inductive content analysis. RESULTS: Survivors cited a strong preference for oncology-based follow-up within the first 5 years after diagnosis, driven by their need for reassurance that cancer had not recurred. Survivors also thought that their primary care provider needed to be involved. Survivors assumed that oncology follow-up was directed by a standard protocol that included streamlining the follow-up team. Survivors recognized that patients with more complex cancers or challenging treatment courses may require more intensive follow-up and deviate from the standard protocol. Most survivors were comfortable deferring decisions regarding who participated in follow-up to the oncology team. CONCLUSIONS: Most patients think a streamlined approach to oncology-based breast cancer follow-up already occurs, driven by a standard protocol. The use of a standard protocol to provide guidance for which types of oncology providers should participate in breast cancer follow-up will streamline care and represents a significant opportunity to reduce unnecessary variation. This approach is especially critical given patients' strong preferences for oncology-based follow-up.

Computational and Experimental Study of Thermodynamics of the Reaction of Titania and Water at High Temperatures.

Gaseous titanium hydroxide and oxyhydroxide species were studied with quantum chemical methods. The results are used in conjunction with an experimental transpiration study of titanium dioxide (TiO2) in water vapor-containing environments at elevated temperatures to provide a thermodynamic description of the Ti(OH)4(g) and TiO(OH)2(g) species. The geometry and harmonic vibrational frequencies of these species were computed using the coupled-cluster singles and doubles method with a perturbative correction for connected triple substitutions [CCSD(T)]. For the OH bending and rotation, the B3LYP density functional theory was used to compute corrections to the harmonic approximations. These results were combined to determine the enthalpy of formation. Experimentally, the transpiration method was used with water contents from 0 to 76 mol % in oxygen or argon carrier gases for 20-250 h exposure times at 1473-1673 K. Results indicate that oxygen is not a key contributor to volatilization, and the primary reaction for volatilization in this temperature range is TiO2(s) + H2O(g) = TiO(OH)2(g). Data were analyzed with both the second and third law methods using the thermal functions derived from the theoretical calculations. The third law enthalpy of formation at 298.15 K for TiO(OH)2(g) at 298 K was -838.9 ± 6.5 kJ/mol, which compares favorably to the theoretical calculation of -838.7 ± 25 kJ/mol. We recommend the experimentally derived third law enthalpy of formation at 298.15 K for TiO(OH)2, the computed entropy of 320.67 J/mol·K, and the computed heat capacity [149.192 + (-0.02539)T + (8.28697 × 10-6)T2 + (-15614.05)/T + (-5.2182 × 10-11)/T2] J/mol-K, where T is the temperature in K.

Coherent coupling between a quantum dot and a donor in silicon.

Individual donors in silicon chips are used as quantum bits with extremely low error rates. However, physical realizations have been limited to one donor because their atomic size causes fabrication challenges. Quantum dot qubits, in contrast, are highly adjustable using electrical gate voltages. This adjustability could be leveraged to deterministically couple donors to quantum dots in arrays of qubits. In this work, we demonstrate the coherent interaction of a 31P donor electron with the electron of a metal-oxide-semiconductor quantum dot. We form a logical qubit encoded in the spin singlet and triplet states of the two-electron system. We show that the donor nuclear spin drives coherent rotations between the electronic qubit states through the contact hyperfine interaction. This provides every key element for compact two-electron spin qubits requiring only a single dot and no additional magnetic field gradients, as well as a means to interact with the nuclear spin qubit.

Implementing Child-focused Activity Meter Utilization into the Elementary School Classroom Setting Using a Collaborative Community-based Approach.

INTRODUCTION: The prevalence of pediatric obesity has increased over the past 3 decades and is a pressing public health program. New technology advancements that can encourage more physical in children are needed. The Zamzee program is an activity meter linked to a motivational website designed for children 8-14 years of age. The objective of the study was to use a collaborative approach between a medical center, the private sector and local school staff to assess the feasibility of using the Zamzee Program in the school-based setting to improve physical activity levels in children. METHODS: This was a pilot 8-week observational study offered to all children in one fifth grade classroom. Body mass index (BMI), the amount of physical activity by 3-day recall survey, and satisfaction with usability of the Zamzee Program were measured pre- and post-study. RESULTS: Out of 11 children who enrolled in the study, 7 completed all study activities. In those who completed the study, the median (interquartile range) total activity time by survey increased by 17 (1042) minutes and the BMI percentile change was 0 (8). Both children and their caregivers found the Zamzee Activity Meter (6/7) and website (6/7) "very easy" or "easy" to use. CONCLUSION: The Zamzee Program was found to be usable but did not significantly improve physical activity levels or BMI. Collaborative obesity intervention projects involving medical centers, the private sector and local schools are feasible but the effectiveness needs to be evaluated in larger-scale studies.

Unicompartmental knee replacement after high tibial osteotomy: Invalidating a contraindication.

The outcome of high tibial osteotomy (HTO) deteriorates with time, and additional procedures may be required. The aim of this study was to compare the clinical and radiological outcomes between unicompartmental knee replacement (UKR) and total knee replacement (TKR) after HTO as well as after primary UKR. A total of 63 patients (63 knees) were studied retrospectively and divided into three groups: UKR after HTO (group A; n = 22), TKR after HTO (group B; n = 18) and primary UKR (group C; n = 22). The Oxford knee score (OKS), Knee Society score (KSS), hip-knee-ankle angles, mechanical axis and patellar height were evaluated pre- and post-operatively. At a mean of 64 months (19 to 180) post-operatively the mean OKS was 43.8 (33 to 49), 43.3 (30 to 48) and 42.5 (29 to 48) for groups A, B and C, respectively (p = 0.73). The mean KSS knee score was 88.8 (54 to 100), 88.11 (51 to 100) and 85.3 (45 to 100) for groups A, B and C, respectively (p = 0.65), and the mean KSS function score was 85.0 (50 to 100) in group A, 85.8 (20 to 100) in group B and 79.3 (50 to 100) in group C (p = 0.48). Radiologically the results were comparable for all groups except for patellar height, with a higher incidence of patella infra following a previous HTO (p = 0.02).

Exact infinite-time statistics of the Loschmidt echo for a quantum quench.

The equilibration dynamics of a closed quantum system is encoded in the long-time distribution function of generic observables. In this Letter we consider the Loschmidt echo generalized to finite temperature, and show that we can obtain an exact expression for its long-time distribution for a closed system described by a quantum XY chain following a sudden quench. In the thermodynamic limit the logarithm of the Loschmidt echo becomes normally distributed, whereas for small quenches in the opposite, quasicritical regime, the distribution function acquires a universal double-peaked form indicating poor equilibration. These findings, obtained by a central limit theorem-type result, extend to completely general models in the small-quench regime.

Transition to chaos of coupled oscillators: an operator fidelity susceptibility study.

The operator fidelity is a measure of the information-theoretic distinguishability between perturbed and unperturbed evolutions. The response of this measure to the perturbation may be formulated in terms of the operator fidelity susceptibility (OFS), a quantity which has been used to investigate the parameter spaces of quantum systems in order to discriminate their regular and chaotic regimes. In this work we numerically study the OFS for a pair of nonlinearly coupled two-dimensional harmonic oscillators, a model which is equivalent to that of a hydrogen atom in a uniform external magnetic field. We show how the two terms of the OFS, being linked to the main properties that differentiate regular from chaotic behavior, allow for the detection of this model's transition between the two regimes. In addition, we find that the parameter interval where perturbation theory applies is delimited from above by a local minimum of one of the analyzed terms.

Fidelity approach to the disordered quantum XY model.

We study the random XY spin chain in a transverse field by analyzing the susceptibility of the ground state fidelity, numerically evaluated through a standard mapping of the model onto quasifree fermions. It is found that the fidelity susceptibility and its scaling properties provide useful information about the phase diagram. In particular it is possible to determine the Ising critical line and the Griffiths phase regions, in agreement with previous analytical and numerical results.

Comparison of long-term outcomes after allogeneic hematopoietic stem cell transplantation from matched sibling and unrelated donors.

Long-term survivors of hematopoietic stem cell transplants remain at risk of potentially fatal complications that detract from life quality. Long-term morbidity and mortality were compared between matched recipient cohorts surviving 2 or more years and defined by donor type, HLA matched sibling donor (MSD) or volunteer unrelated donor (URD). Patients were previously entered into the prospective multicenter International Unrelated Search and Transplant Study. Thirty-nine centers provided data on 108 URD and 355 MSD recipients surviving more than 2 years. Long-term survival, performance status, chronic GvHD (c-GvHD), secondary malignancy, endocrine dysfunction, cataracts, bone necrosis and dental pathology were compared between cohorts. Twelve year survival was 77+/-5% for the MSD and 67+/-11% for the URD cohort (P=0.1). Late death occurred in 105 of 463 recipients alive at 2 years, 73 after 355 (21%) MSD and 32 after 108 (30%) URD transplants, P=0.10. Of 105 deaths, the cause was relapse in 60 and unrelated to relapse in 45 cases. Cumulative incidence of extensive c-GvHD (P=0.002), cataracts (P=0.02) and bone necrosis (P=0.02) was higher after URD transplants. No long-term difference in endocrine dysfunction, secondary malignancy and major dental pathology was detected. This landmark study will assist physicians counseling patients pre-transplant and with their long-term care post transplant.

Nanowire acting as a superconducting quantum interference device.

We present the results from an experimental study of the magnetotransport of superconducting wires of amorphous indium-oxide having widths in the range 40-120 nm. We find that, below the superconducting transition temperature, the wires exhibit clear, reproducible, oscillations in their resistance as a function of magnetic field. The oscillations are reminiscent of those that underlie the operation of a superconducting quantum interference device.

Van der Waals density functional for layered structures.

To understand sparse systems, we must account for both strong local atom bonds and weak nonlocal van der Waals forces between atoms separated by empty space. A fully nonlocal functional form [Phys. Rev. B 62, 6997 (2000)]] of density-functional theory (DFT) is applied here to the layered systems graphite, boron nitride, and molybdenum sulfide to compute bond lengths, binding energies, and compressibilities. These key examples show that the DFT with the generalized-gradient approximation does not apply for calculating properties of sparse matter, while use of the fully nonlocal version appears to be one way to proceed.

Delayed secondary glucocorticoid responsiveness of MYOC in human trabecular meshwork cells.

PURPOSE: To characterize the glucocorticoid responsiveness of the glaucoma gene MYOC (myocilin/TIGR) in cultured human trabecular meshwork (TM) cells. METHODS: MYOC expression in two independently derived human TM cell lines was quantified by Western immunoblot analysis of protein levels and quantitative PCR analysis of mRNA levels. Promoter activity was measured indirectly with the luciferase reporter gene in a dual luciferase reporter assay. RESULTS: Application of the synthetic glucocorticoid dexamethasone (Dex) to cultured TM cells at 100 nM resulted in a delayed (8-16 hours) induction of myocilin. The concentration dependence (median effective concentration [EC(50)], approximately 10 nM) and reversal by the glucocorticoid antagonist, RU486, implicates the glucocorticoid receptor (GR). In an interesting observation, RU486 alone acted as a partial agonist to MYOC expression. Treatment of TM cells with the protein synthesis inhibitor cycloheximide abolished the Dex induction, suggesting an indirect effect of the GR on MYOC expression. In addition, the RNA synthesis inhibitor actinomycin D also blocked Dex induction, indicating that the Dex effect was due to increased MYOC transcription. Analysis of up to 2700 nucleotides (nt) of the MYOC gene 5'-flanking region in luciferase reporter constructs showed no Dex induction, despite the presence of multiple putative glucocorticoid response element (GRE)-like half-sites in the MYOC promoter and the presence of an intact cellular GR-mediated signaling system. CONCLUSIONS: MYOC is a delayed secondary glucocorticoid-responsive gene. Characterization of the transcription factors that mediate the secondary response will shed new light on the pathophysiology of steroid-induced ocular hypertension and glaucoma.

Care-as-service, care-as-relating, care-as-comfort: understanding nursing home residents' definitions of quality.

PURPOSE: This study explored how nursing home residents define quality of care. DESIGN AND METHODS: Data were collected through in-depth interviews and were analyzed using grounded dimensional analysis. RESULTS: Residents defined quality in three ways: (a) Care-as-service residents focused on instrumental aspects of care. They assessed quality using the parameters of efficiency, competence, and value. (b) Care-as-relating residents emphasized the affective aspects of care, defining quality as care that demonstrated friendship and allowed them to show reciprocity with their caregivers. (c) Care-as-comfort residents defined quality as care that allowed them to maintain their physical comfort, a state that required minute and often repetitive adjustments in response to their bodily cues. IMPLICATIONS: Residents' perceptions of care quality have implications for long-term care practice. The integration of these perceptions into quality assurance instruments could improve the usefulness of tools designed to obtain resident input.

Glucocorticoid induction of the glaucoma gene MYOC in human and monkey trabecular meshwork cells and tissues.

PURPOSE: To examine the intracellular and extracellular expression of myocilin in the human and primate trabecular meshwork (TM) in the presence and absence of glucocorticoids. METHODS: Myocilin expression was examined in cultured human TM cells by Northern blot analysis and myocilin antibody-mediated immunoprecipitation. Myocilin expression was quantified using high-resolution two-dimensional polyacrylamide gel electrophoresis of radiolabeled proteins from human TM cells, TM tissue explants, and perfused human anterior segments cultured with and without dexamethasone (DEX) for 14 to 21 days, as well as TM tissue from pigtailed monkeys treated orally for 1 year with cortisone acetate. Immunofluorescence with anti-myocilin antibodies was used to localize cellular and extracellular expression of myocilin in cultured human TM cells. RESULTS: Glucocorticoid treatment caused a significant induction of myocilin mRNA, a tetrad of cell-associated proteins, and 8 to 20 secreted proteins (molecular mass [M(r)] 56 and 59 kDa and isoelectric point [pI] 5.2 and 5.3) in some, but not all the cultured human TM cells and explanted tissues. Western immunoblot analysis using anti-myocilin peptide antibodies identified these proteins as encoded by the MYOC gene. There was significant induction of the myocilin proteins in three perfusion-cultured human eyes, in which DEX-induced elevated intraocular pressure developed. Monkeys treated 1 year with cortisol acetate showed steroid glaucoma-like morphologic changes in the TM that correlated with the induction of myocilin in the TM. Immunofluorescence analysis of cultured TM cells localized myocilin intracellularly in discrete perinuclear and cytoplasmic vesicular deposits as well as extracellularly on the cell surface associated with the extracellular matrix. In several DEX-treated TM cell lines, there were significant levels of myocilin secreted into the media. Enzymatic deglycosylation of proteins in the TM media converted the higher molecular weight isoforms of myocilin (approximately 57 kDa) to the lower molecular weight isoforms ( approximately 55 kDa). CONCLUSIONS: Although the function of myocilin is unknown, induction of these TM proteins was found in eyes in which glucocorticoid-induced ocular hypertension developed. Therefore, myocilin may play an important pathogenic role in ocular hypertension in addition to its role in certain forms of POAG.