11,851 research outputs found

    Understanding Caregiver Factors Influencing Childhood Influenza Vaccination

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    Influenza is a contagious disease that affects approximately 30% to 40% of American children yearly, and all children 18 and under are recommended to be vaccinated. Through the use of a survey tool, 119 responses were collected about the factors that influence the decisions of caregivers whether or not to vaccinate their children against influenza. The knowledge generated from the survey may be used to formulate education programs to increase vaccination rates

    Anisotropic Stark Effect and Electric-Field Noise Suppression for Phosphorus Donor Qubits in Silicon

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    We report the use of novel, capacitively terminated coplanar waveguide (CPW) resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them

    Addressing spin transitions on 209Bi donors in silicon using circularly-polarized microwaves

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    Over the past decade donor spin qubits in isotopically enriched 28^{28}Si have been intensely studied due to their exceptionally long coherence times. More recently bismuth donor electron spins have become popular because Bi has a large nuclear spin which gives rise to clock transitions (first-order insensitive to magnetic field noise). At every clock transition there are two nearly degenerate transitions between four distinct states which can be used as a pair of qubits. Here it is experimentally demonstrated that these transitions are excited by microwaves of opposite helicity such that they can be selectively driven by varying microwave polarization. This work uses a combination of a superconducting coplanar waveguide (CPW) microresonator and a dielectric resonator to flexibly generate arbitrary elliptical polarizations while retaining the high sensitivity of the CPW

    Developments in electromagnetic tomography instrumentation.

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    A new EMT sensor and instrumentation is described which combines the best features of previous systems and has a modular structure to allow for future system expansion and development

    Spin relaxation and coherence times for electrons at the Si/SiO2 interface

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    While electron spins in silicon heterostructures make attractive qubits, little is known about the coherence of electrons at the Si/SiO2 interface. We report spin relaxation (T1) and coherence (T2) times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1 and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by a factor of two. The quantum dot T2 is shorter than T1, indicating that T2 is not controlled by T1 at 350 mK but is instead limited by an extrinsic mechanism. The evidence suggests that this extrinsic mechanism is an exchange interaction between electrons in neighboring dots.Comment: Extended with more experiments and rewritten. 6 pages, 5 figures, to be submitted to Phys. Rev.

    Spin Coherence and 14^{14}N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR

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    Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV^-) in diamonds at X-band magnetic fields (280-400 mT) and low temperatures (2-70 K). The NV^- centers in synthetic type IIb diamonds (nitrogen impurity concentration <1<1~ppm) are prepared with bulk concentrations of 210132\cdot 10^{13} cm3^{-3} to 410144\cdot 10^{14} cm3^{-3} by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000^\circC for 60 mins) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV^-s. After the annealing, spin coherence times of T2=0.74_2 = 0.74~ms at 5~K are achieved, being only limited by 13^{13}C nuclear spectral diffusion in natural abundance diamonds. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central 14^{14}N nucleus. The ESEEM spectral analysis allows for accurate determination of the 14^{14}N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal 13^{13}C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective 13^{13}C hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure