175 research outputs found
Valley interference effects on a donor electron close to a Si/SiO2 interface
We analyze the effects of valley interference on the quantum control and
manipulation of an electron bound to a donor close to a Si/SiO2 interface as a
function of the valley-orbit coupling at the interface. We find that, for
finite valley-orbit coupling, the tunneling times involved in shuttling the
electron between the donor and the interface oscillate with the interface/donor
distance in much the same way as the exchange coupling oscillates with the
interdonor distance. These oscillations disappear when the ground state at the
interface is degenerate (corresponding to zero valley-orbit coupling).Comment: 7 pages, 5 figure
Theory of one and two donors in Silicon
We provide here a roadmap for modeling silicon nano-devices with one or two
group V donors (D). We discuss systems containing one or two electrons, that
is, D^0, D^-, D_2^+ and D_2^0 centers. The impact of different levels of
approximation is discussed. The most accurate instances -- for which we provide
quantitative results -- are within multivalley effective mass including the
central cell correction and a configuration interaction account of the
electron-electron correlations. We also derive insightful, yet less accurate,
analytical approximations and discuss their validity and limitations -- in
particular, for a donor pair, we discuss the single orbital LCAO method, the
Huckel approximation and the Hubbard model. Finally we discuss the connection
between these results and recent experiments on few dopant devices.Comment: 13 pages, 6 figure
Moving frames for cotangent bundles
Cartan's moving frames method is a standard tool in riemannian geometry. We
set up the machinery for applying moving frames to cotangent bundles and its
sub-bundles defined by non-holonomic constraints.Comment: 13 pages, to appear in Rep. Math. Phy
Electric field driven donor-based charge qubits in semiconductors
We investigate theoretically donor-based charge qubit operation driven by
external electric fields. The basic physics of the problem is presented by
considering a single electron bound to a shallow-donor pair in GaAs: This
system is closely related to the homopolar molecular ion H_2^+. In the case of
Si, heteropolar configurations such as PSb^+ pairs are also considered. For
both homopolar and heteropolar pairs, the multivalley conduction band structure
of Si leads to short-period oscillations of the tunnel-coupling strength as a
function of the inter-donor relative position. However, for any fixed donor
configuration, the response of the bound electron to a uniform electric field
in Si is qualitatively very similar to the GaAs case, with no valley quantum
interference-related effects, leading to the conclusion that electric field
driven coherent manipulation of donor-based charge qubits is feasible in
semiconductors
Magnetic field-assisted manipulation and entanglement of Si spin qubits
Architectures of donor-electron based qubits in silicon near an oxide
interface are considered theoretically. We find that the precondition for
reliable logic and read-out operations, namely the individual identification of
each donor-bound electron near the interface, may be accomplished by
fine-tuning electric and magnetic fields, both applied perpendicularly to the
interface. We argue that such magnetic fields may also be valuable in
controlling two-qubit entanglement via donor electron pairs near the interface.Comment: 4 pages, 4 figures. 1 ref and 1 footnote adde
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