281 research outputs found
Valley and spin polarization from graphene line defect scattering
Quantum transport calculations describing electron scattering off an extended
line defect in graphene are presented. The calculations include potentials from
local magnetic moments recently predicted to exist on sites adjacent to the
line defect. The transmission probability is derived and expressed as a
function of valley, spin, and angle of incidence of an electron at the Fermi
level being scattered. It is shown that the previously predicted valley
polarization in a beam of transmitted electrons is not significantly influenced
by the presence of the magnetic moments. These moments, however, do introduce
some spin polarization, in addition to the valley polarization, albeit no more
than about 20%.Comment: 6 pages, 4 figure
Graphene valley filter using a line defect
With its two degenerate valleys at the Fermi level, the band structure of
graphene provides the opportunity to develop unconventional electronic
applications. Herein, we show that electron and hole quasiparticles in graphene
can be filtered according to which valley they occupy without the need to
introduce confinement. The proposed valley filter is based on scattering off a
recently observed line defect in graphene. Quantum transport calculations show
that the line defect is semitransparent and that quasiparticles arriving at the
line defect with a high angle of incidence are transmitted with a valley
polarization near 100%.Comment: 5 pages, 4 figure
Room-temperature ballistic transport in narrow graphene strips
We investigate electron-phonon couplings, scattering rates, and mean free
paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our
calculations for these graphene nanostrips show both the expected similarity
with single-wall carbon nanotubes (SWNTs) and the suppression of the
electron-phonon scattering due to a Dirichlet boundary condition that prohibits
one major backscattering channel present in SWNTs. Low-energy acoustic phonon
scattering is exponentially small at room temperature due to the large phonon
wave vector required for backscattering. We find within our model that the
electron-phonon mean free path is proportional to the width of the nanostrip
and is approximately 70 m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure
Entanglement between static and flying qubits in a semiconducting carbon nanotube
Entanglement can be generated by two electrons in a spin-zero state on a
semiconducting single-walled carbon nanotube. The two electrons, one weakly
bound in a shallow well in the conduction band, and the other injected into the
conduction band, are coupled by the Coulomb interaction. Both transmission and
entanglement are dependent on the well characteristics, which can be controlled
by a local gate, and on the kinetic energy of the injected electron. Regimes
with different degrees of electron correlation exhibit full or partial
entanglement. In the latter case, the maximum entanglement can be estimated as
a function of width and separation of a pair of singlet-triplet resonances.Comment: 17 pages and 12 figures, accepted to J. Phys. Cond. Ma
Cascaded variational quantum eigensolver algorithm
We present a cascaded variational quantum eigensolver algorithm that only
requires the execution of a set of quantum circuits once rather than at every
iteration during the parameter optimization process, thereby reducing the
number of needed circuit executions. This algorithm lets a quantum processing
unit probe all the needed probability mass functions and a classical processing
unit perform all the remaining calculations, including the variational
optimization. The ansatz form does not restrict the solution space and provide
full control over the parameter space, including the implementation of symmetry
and other physically motivated constraints.Comment: 5 pages, 2 figure
Implementing Jastrow--Gutzwiller operators on a quantum computer using the cascaded variational quantum eigensolver algorithm
A Jastrow--Gutzwiller operator adds many-body correlations to a quantum
state. However, the operator is non-unitary, making it difficult to implement
directly on a quantum computer. We present a novel implementation of the
Jastrow--Gutzwiller operator using the cascaded variational quantum eigensolver
algorithm. We demonstrate the method on IBM Q Lagos for a Hubbard model
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