88 research outputs found
Quantum information processing based on P-31 nuclear spin qubits in a quasi-one-dimensional Si-28 nanowire
We suggest a new method of quantum information processing based on the
precise placing of P-31 isotope atoms in a quasi-one-dimensional Si-28 nanowire
using isotope engineering and neutron-transmutation doping of the grown
structures. In our structure, interqubit entanglement is based on the indirect
interaction of P-31 nuclear spins with electrons localized in a nanowire. This
allows one to control the coupling between distant qubits and between qubits
separated by non-qubit neighboring nodes. The suggested method enables one to
fabricate structures using present-day nanolithography. Numerical estimates
show the feasibility of the proposed device and method of operation.Comment: 7 pages, 4 figure
Isotopically engineered silicon/silicon-germanium nanostructures as basic elements for a nuclear spin quantum computer
The idea of quantum computation is the most promising recent developments in
the high-tech domain, while experimental realization of a quantum computer
poses a formidable challenge. Among the proposed models especially attractive
are semiconductor based nuclear spin quantum computer's (S-NSQC), where nuclear
spins are used as quantum bistable elements, ''qubits'', coupled to the
electron spin and orbital dynamics. We propose here a scheme for implementation
of basic elements for S-NSQC's which are realizable within achievements of the
modern nanotechnology. These elements are expected to be based on a
nuclear-spin-controlled isotopically engineered Si/SiGe heterojunction, because
in these semiconductors one can vary the abundance of nuclear spins by
engineering the isotopic composition. A specific device is suggested, which
allows one to model the processes of recording, reading and information
transfer on a quantum level using the technique of electrical detection of the
magnetic state of nuclear spins. Improvement of this technique for a
semiconductor system with a relatively small number of nuclei might be applied
to the manipulation of nuclear spin ''qubits'' in the future S-NSQC.Comment: 11 pages, 2 figures, PostScript, GS vie
Fluctuation-Stimulated Variable-Range Hopping
Qualitatively new transport mechanism is suggested for hopping of carriers
according to which the variable-range hopping (VRH) arises from the resonant
tunneling between transport states brought into resonance by Coulomb potentials
produced by surrounding sites with fluctuating occupations. A semiquantitative
description of the hopping transport is given based on the assumption that
fluctuations of energies of hopping sites have spectral density 1/f
Transverse "resistance overshoot" in a Si/SiGe two-dimensional electron gas in the quantum Hall effect regime
We investigate the peculiarities of the "overshoot" phenomena in the
transverse Hall resistance R_{xy} in Si/SiGe. Near the low magnetic field end
of the quantum Hall effect plateaus, when the filling factor \nu approaches an
integer i, R_{xy} overshoots the normal plateau value h/ie^2. However, if
magnetic field B increases further, R_{xy} decreases to its normal value. It is
shown that in the investigated sample n-Si/Si_{0.7}Ge_{0.3}, overshoots exist
for almost all \nu. Existence of overshoot in R_{xy} observed in different
materials and for different \nu, where splitting of the adjacent Landau bands
has different character, hints at the common origin of this effect. Comparison
of the experimental curves R_{xy}(\nu) for \nu = 3 and \nu = 5 with and without
overshoot showed that this effect exist in the whole interval between plateaus,
not only in the region where R_{xy} exceeds the normal plateau value.Comment: 3 pages, 5 EPS figure
Structure and spatial distribution of Ge nanocrystals subjected to fast neutron irradiation
The influence of fast neutron irradiation on the structure and spatial
distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has
been studied. The investigation was conducted by means of laser Raman
Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and
X-ray photoelectron spectroscopy (XPS). The irradiation of NC-Ge samples by a
high dose of fast neutrons lead to a partial destruction of the nanocrystals.
Full reconstruction of crystallinity was achieved after annealing the radiation
damage at 800 deg. C, which resulted in full restoration of the RS spectrum.
HR-TEM images show, however, that the spatial distributions of NC-Ge changed as
a result of irradiation and annealing. A sharp decrease in NC distribution
towards the SiO2 surface has been observed. This was accompanied by XPS
detection of Ge oxides and elemental Ge within both the surface and subsurface
region
Electron transport in a slot-gate Si MOSFET
The transversal and longitudinal resistance in the quantum Hall effect regime
was measured in a Si MOSFET sample in which a slot-gate allows one to vary the
electron density and filling factor in different parts of the sample. In case
of unequal gate voltages, the longitudinal resistances on the opposite sides of
the sample differ from each other because the originated Hall voltage
difference is added to the longitudinal voltage only on one side depending on
the gradient of the gate voltages and the direction of the external magnetic
field. After subtracting the Hall voltage difference, the increase in
longitudinal resistance is observed when electrons on the opposite sides of the
slot occupy Landau levels with different spin orientations.Comment: To appear in Europhys. Let
- …