Significant advances have been made towards fault-tolerant operation of silicon spin qubits, with single qubit fidelities exceeding 99.9%, several demonstrations of two-qubit gates based on exchange ...coupling, and the achievement of coherent single spin-photon coupling. Coupling arbitrary pairs of spatially separated qubits in a quantum register poses a significant challenge as most qubit systems are constrained to two dimensions with nearest neighbor connectivity. For spins in silicon, new methods for quantum state transfer should be developed to achieve connectivity beyond nearest-neighbor exchange. Here we demonstrate shuttling of a single electron across a linear array of nine series-coupled silicon quantum dots in ~50 ns via a series of pairwise interdot charge transfers. By constructing more complex pulse sequences we perform parallel shuttling of two and three electrons at a time through the array. These experiments demonstrate a scalable approach to physically transporting single electrons across large silicon quantum dot arrays.
We characterize a fluxonium qubit consisting of a Josephson junction inductively shunted with a NbTiN nanowire superinductance. We explain the measured energy spectrum by means of a multimode theory ...accounting for the distributed nature of the superinductance and the effect of the circuit nonlinearity to all orders in the Josephson potential. Using multiphoton Raman spectroscopy, we address multiple fluxonium transitions, observe multilevel Autler-Townes splitting and measure an excited state lifetime of T_{1}=20 μs. By measuring T_{1} at different magnetic flux values, we find a crossover in the lifetime limiting mechanism from capacitive to inductive losses.
We report on a quantum dot device design that combines the low disorder properties of undoped SiGe heterostructure materials with an overlapping gate stack in which each electrostatic gate has a ...dominant and unique function-control of individual quantum dot occupancies and of lateral tunneling into and between dots. Control of the tunneling rate between a dot and an electron bath is demonstrated over more than nine orders of magnitude and independently confirmed by direct measurement within the bandwidth of our amplifiers. The inter-dot tunnel coupling at the charge configuration anti-crossing is directly measured to quantify the control of a single inter-dot tunnel barrier gate. A simple exponential dependence is sufficient to describe each of these tunneling processes as a function of the controlling gate voltage.
We perform detailed magnetotransport studies on two-dimensional electron gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify the electron mobility limiting mechanisms. By ...analyzing data from 26 different heterostructures, we observe a strong correlation between the background oxygen concentration in the Si quantum well and the maximum mobility. The highest-quality wafer supports a 2DEG with mobility mu = 160 000 cm super(2)/Vs at a density n = 2.17 x 10 super(11)/cm super(2) and exhibits a metal-to-insulator transition at a critical density n sub(c)= 0.46 x 10 super(11)/cm super(2). We extract a valley splitting Delta sub()v~ 150 mu eV at a magnetic field B = 1.8 T. These results provide evidence that undoped Si/SiGe heterostructures are suitable for the fabrication of few-electron quantum dots.
Abstract Background context The multiplicity of biopsychosocial and economic facets of chronic disabling back and/or neck pain complicates the treatment outcomes measurement. Our previous work showed ...that personal functional goal achievement contributed more toward patient satisfaction with the outcome than did traditional self-reports of pain and physical function or measured strength, flexibility, and endurance among functional restoration program (FRP) graduates with chronic disabling back and/or neck pain. Purpose The primary goal was to compare the impact on patient satisfaction of pain and functional goal achievement versus self-reports of pain and physical function. Study design This was an observational study of all patients with chronic disabling back and/or neck pain completing an FRP between June 2008 and May 2009. Outcome measures Before the treatment, participants recorded personal 3-month goals for pain, work, recreation, and activities of daily living. At least 3 months later, all graduates were sent a follow-up survey displaying the patient's pretreatment functional goals and eliciting the patient's assessment of functional goal achievement; current pain magnitude, “satisfaction with the overall results for your pain problem;” and responses to the Short Form-36v2 Physical Functioning subscale (PF-10). Methods Pain goal achievement was calculated as the difference between the pretreatment pain goal and follow-up pain magnitude. Linear regression was used to evaluate the association between satisfaction and four variables (follow-up pain; PF-10; pain goal achievement; functional goal achievement), individually and then together in a full model. Results Of the 82 patients surveyed, 62 responded completely. Mean age was 44 years, with 48% female and 35% on worker's compensation. The model R2 combining all four variables explained 0.6033 of the variance in satisfaction. Each variable by itself was significantly related to patient satisfaction at p<.001, but the overlap in association was large. The unique contributions (R2 ) to the variation in satisfaction were the following: functional goal achievement: 0.0471; PF-10 score: 0.0229; pain magnitude: 0.0178; and pain goal achievement: 0.0020. Conclusions At least 3 months after the treatment, functional goal achievement had by far the greatest impact on patient satisfaction, followed by PF-10 score, pain magnitude, and, finally, pain goal achievement. Functional goal achievement has great potential as a tool for patient-centered treatment decision-making and outcomes measurement for people with chronic disabling back and/or neck pain and their health care providers.
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