990 research outputs found
Surface code architecture for donors and dots in silicon with imprecise and nonuniform qubit couplings
A scaled quantum computer with donor spins in silicon would benefit from a
viable semiconductor framework and a strong inherent decoupling of the qubits
from the noisy environment. Coupling neighbouring spins via the natural
exchange interaction according to current designs requires gate control
structures with extremely small length scales. We present a silicon
architecture where bismuth donors with long coherence times are coupled to
electrons that can shuttle between adjacent quantum dots, thus relaxing the
pitch requirements and allowing space between donors for classical control
devices. An adiabatic SWAP operation within each donor/dot pair solves the
scalability issues intrinsic to exchange-based two-qubit gates, as it does not
rely on sub-nanometer precision in donor placement and is robust against noise
in the control fields. We use this SWAP together with well established global
microwave Rabi pulses and parallel electron shuttling to construct a surface
code that needs minimal, feasible local control.Comment: Published version - more detailed discussions, robustness to
dephasing pointed out additionall
Spin Coherence and N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR
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 ~ppm) are prepared with
bulk concentrations of cm to cm
by high-energy electron irradiation and subsequent annealing. We find that a
proper post-radiation anneal (1000C for 60 mins) is critically
important to repair the radiation damage and to recover long electron spin
coherence times for NVs. After the annealing, spin coherence times of T~ms at 5~K are achieved, being only limited by 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 N nucleus. The ESEEM spectral analysis allows for accurate
determination of the N nuclear hypefine and quadrupole tensors. In
addition, the ESEEM effects from two proximal C sites (second-nearest
neighbor and fourth-nearest neighbor) are resolved and the respective C
hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure
Critical issues in the formation of quantum computer test structures by ion implantation
The formation of quantum computer test structures in silicon by ion
implantation enables the characterization of spin readout mechanisms with
ensembles of dopant atoms and the development of single atom devices. We
briefly review recent results in the characterization of spin dependent
transport and single ion doping and then discuss the diffusion and segregation
behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy
implantations as characterized through depth profiling by secondary ion mass
spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the
SiO2/Si interface during activation anneals, while antimony diffusion is found
to be minimal. An effect of the ion charge state on the range of antimony ions,
121Sb25+, in SiO2/Si is also discussed
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Emission of secondary particles from metals and insulators at impact of slow highly charged ions
Emission of secondary electrons and ions from clean Au, CxHy-Au, and SiO{sub 2} surfaces at impact of slow (v{approx}0.3 v{sub Bohr}) ions were measured as function of incident ion charge for 1+{le}q{le}75+. Electron yields from thermal SiO{sub 2} films (150 mm on Si) were found to be lower than those from the other two for q>3+. Yields of negative secondary ions from SiO{sub 2} and CxHy-Au were recorded in parallel with electron emission data and exhibit a q{sub 4} dependency on incident ion charge. Direct comparison of collisional and electronic contributions to secondary ion production from SiO{sub 2} films using a beam of charge state equilibrated Xe (at 2.75 keV/u) shows positive and negative secondary ion yield increases with incident ion charge of >400. Results are discussed in relation to key signatures of electronic sputtering by Coulomb explosions
Detection of low energy single ion impacts in micron scale transistors at room temperature
We report the detection of single ion impacts through monitoring of changes
in the source-drain currents of field effect transistors (FET) at room
temperature. Implant apertures are formed in the interlayer dielectrics and
gate electrodes of planar, micro-scale FETs by electron beam assisted etching.
FET currents increase due to the generation of positively charged defects in
gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel
regions. Implant damage is repaired by rapid thermal annealing, enabling
iterative cycles of device doping and electrical characterization for
development of single atom devices and studies of dopant fluctuation effects
Process improvement in SMEs: The impact of harmonious passion for entrepreneurship, employee creative self-efficacy, and time spent innovating
Harmonious passion, creative self-efficacy, and time spent innovating are examined as antecedents to innovative process improvement suggestions in a field study of 213 employees in an SME. Results show that time spent innovating, or thinking about and experimenting with new ideas, predicts the number of process improvement suggestions. Time spent innovating is, itself, influenced by the employee’s level of harmonious passion for entrepreneurship, moderated by creative self-efficacy. Counter to expectations, the moderation was negative; such that the positive relationship between harmonious passion and time spent innovating became weaker as creative self-efficacy became stronger. The results provide insight into the complex relationships between passion, competency, and entrepreneurial behavior and suggest the need for additional focus on the processes employees follow to engage in workplace innovation. In doing so, this study makes three specific contributions. First, it provides a fundamental step toward understanding the role harmonious passion plays in innovation in an SME context. Second, it begins to explain the relationship between individuals’ thoughts, behaviors, and outcomes in the nascent stages of innovation in SMEs. Finally, it provides insight into the heretofore unexplored link between passion and creative self-efficacy in fostering innovative behavior. 
Processing Issues in Top-Down Approaches to Quantum Computer Development in Silicon
We describe critical processing issues in our development of single atom
devices for solid-state quantum information processing. Integration of single
31P atoms with control gates and single electron transistor (SET) readout
structures is addressed in a silicon-based approach. Results on electrical
activation of low energy (15 keV) P implants in silicon show a strong dose
effect on the electrical activation fractions. We identify dopant segregation
to the SiO2/Si interface during rapid thermal annealing as a dopant loss
channel and discuss measures of minimizing it. Silicon nanowire SET pairs with
nanowire width of 10 to 20 nm are formed by electron beam lithography in SOI.
We present first results from Coulomb blockade experiments and discuss issues
of control gate integration for sub-40nm gate pitch levels
Absolute calibration of GafChromic film for very high flux laser driven ion beams.
We report on the calibration of GafChromic HD-v2 radiochromic film in the extremely high dose regime up to 100 kGy together with very high dose rates up to 7 × 1011 Gy/s. The absolute calibration was done with nanosecond ion bunches at the Neutralized Drift Compression Experiment II particle accelerator at Lawrence Berkeley National Laboratory (LBNL) and covers a broad dose dynamic range over three orders of magnitude. We then applied the resulting calibration curve to calibrate a laser driven ion experiment performed on the BELLA petawatt laser facility at LBNL. Here, we reconstructed the spatial and energy resolved distributions of the laser-accelerated proton beams. The resulting proton distribution is in fair agreement with the spectrum that was measured with a Thomson spectrometer in combination with a microchannel plate detector
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