281 research outputs found
Electrical detection of spin echoes for phosphorus donors in silicon
The electrical detection of spin echoes via echo tomography is used to
observe decoherence processes associated with the electrical readout of the
spin state of phosphorus donor electrons in silicon near a SiO interface.
Using the Carr-Purcell pulse sequence, an echo decay with a time constant of
is observed, in good agreement with theoretical modeling
of the interaction between donors and paramagnetic interface states. Electrical
spin echo tomography thus can be used to study the spin dynamics in realistic
spin qubit devices for quantum information processing.Comment: 14 pages, 3 figure
Electron Paramagnetic Resonance of Boron Acceptors in Isotopically Purified Silicon
The electron paramagnetic resonance (EPR) linewidths of B acceptors in Si are
found to reduce dramatically in isotopically purified 28Si single crystals.
Moreover, extremely narrow substructures in the EPR spectra are visible
corresponding to either an enhancement or a reduction of the absorbed microwave
on resonance. The origin of the substructures is attributed to a combination of
simultaneous double excitation and spin relaxation in the four level spin
system of the acceptors. A spin population model is developed which
qualitatively describes the experimental results.Comment: 4 pages, 3 figure
External field control of donor electron exchange at the Si/SiO2 interface
We analyze several important issues for the single- and two-qubit operations
in Si quantum computer architectures involving P donors close to a SiO2
interface. For a single donor, we investigate the donor-bound electron
manipulation (i.e. 1-qubit operation) between the donor and the interface by
electric and magnetic fields. We establish conditions to keep a donor-bound
state at the interface in the absence of local surface gates, and estimate the
maximum planar density of donors allowed to avoid the formation of a
2-dimensional electron gas at the interface. We also calculate the times
involved in single electron shuttling between the donor and the interface. For
a donor pair, we find that under certain conditions the exchange coupling (i.e.
2-qubit operation) between the respective electron pair at the interface may be
of the same order of magnitude as the coupling in GaAs-based two-electron
double quantum dots where coherent spin manipulation and control has been
recently demonstrated (for example for donors ~10 nm below the interface and
\~40 nm apart, J~10^{-4} meV), opening the perspective for similar experiments
to be performed in Si.Comment: 11 pages, 15 figures. Changes in Eq. 24 plus minor typo
Phosphorus donors in highly strained silicon
The hyperfine interaction of phosphorus donors in fully strained Si thin
films grown on virtual SiGe substrates with is
determined via electrically detected magnetic resonance. For highly strained
epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly
below the limit predicted by valley repopulation. Within a Green's function
approach, density functional theory (DFT) shows that the additional reduction
is caused by the volume increase of the unit cell and a local relaxation of the
Si ligands of the P donor.Comment: 12 pages, 3 figure
Coalescence in the 1D Cahn-Hilliard model
We present an approximate analytical solution of the Cahn-Hilliard equation
describing the coalescence during a first order phase transition. We have
identified all the intermediate profiles, stationary solutions of the noiseless
Cahn-Hilliard equation. Using properties of the soliton lattices, periodic
solutions of the Ginzburg-Landau equation, we have construct a family of ansatz
describing continuously the processus of destabilization and period doubling
predicted in Langer's self similar scenario
Using MGA to shorten the beef breeding season (2002)
Modified conventional synchronization systems for beef cows boost fertility and increase the total number of females that can be inseminated.New March 2002 -- Extension website
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