821 research outputs found
Donor Electron Wave Functions for Phosphorus in Silicon: Beyond Effective Mass Theory
We calculate the electronic wave-function for a phosphorus donor in silicon
by numerical diagonalisation of the donor Hamiltonian in the basis of the pure
crystal Bloch functions. The Hamiltonian is calculated at discrete points
localised around the conduction band minima in the reciprocal lattice space.
Such a technique goes beyond the approximations inherent in the effective-mass
theory, and can be modified to include the effects of altered donor impurity
potentials, externally applied electro-static potentials, as well as the
effects of lattice strain. Modification of the donor impurity potential allows
the experimentally known low-lying energy spectrum to be reproduced with good
agreement, as well as the calculation of the donor wavefunction, which can then
be used to calculate parameters important to quantum computing applications.Comment: 10 pages, 5 figure
Valley Splitting Theory of SiGe/Si/SiGe Quantum Wells
We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an
emphasis on calculating the valley splitting. The theory introduces a valley
coupling parameter, , which encapsulates the physics of the quantum well
interface. The new effective mass parameter is computed by means of a tight
binding theory. The resulting formalism provides rather simple analytical
results for several geometries of interest, including a finite square well, a
quantum well in an electric field, and a modulation doped two-dimensional
electron gas. Of particular importance is the problem of a quantum well in a
magnetic field, grown on a miscut substrate. The latter may pose a numerical
challenge for atomistic techniques like tight-binding, because of its
two-dimensional nature. In the effective mass theory, however, the results are
straightforward and analytical. We compare our effective mass results with
those of the tight binding theory, obtaining excellent agreement.Comment: 13 pages, 7 figures. Version submitted to PR
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
The negatively charged nitrogen-vacancy centre is a unique defect in diamond
that possesses properties highly suited to many applications, including quantum
information processing, quantum metrology, and biolabelling. Although the
unique properties of the centre have been extensively documented and utilised,
a detailed understanding of the physics of the centre has not yet been
achieved. Indeed there persists a number of points of contention regarding the
electronic structure of the centre, such as the ordering of the dark
intermediate singlet states. Without a sound model of the centre's electronic
structure, the understanding of the system's unique dynamical properties can
not effectively progress. In this work, the molecular model of the defect
centre is fully developed to provide a self consistent model of the complete
electronic structure of the centre. The application of the model to describe
the effects of electric, magnetic and strain interactions, as well as the
variation of the centre's fine structure with temperature, provides an
invaluable tool to those studying the centre and a means to design future
empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table
Loss of Spin Entanglement For Accelerated Electrons in Electric and Magnetic Fields
Using an open quantum system we calculate the time dependence of the
concurrence between two maximally entangled electron spins with one accelerated
uniformly in the presence of a constant magnetic field and the other at rest
and isolated from fields. We find at high Rindler temperature the proper time
for the entanglement to be extinguished is proportional to the inverse of the
acceleration cubed.Comment: 10 pages, 4 figures, appendix and other discussion added, fixed some
typographical errors and some references were correcte
High speed quantum gates with cavity quantum electrodynamics
Cavity quantum electrodynamic schemes for quantum gates are amongst the
earliest quantum computing proposals. Despite continued progress, and the
dramatic recent demonstration of photon blockade, there are still issues with
optimal coupling and gate operation involving high-quality cavities. Here we
show dynamic control techniques that allow scalable cavity-QED based quantum
gates, that use the full bandwidth of the cavities. When applied to quantum
gates, these techniques allow an order of magnitude increase in operating
speed, and two orders of magnitude reduction in cavity Q, over passive
cavity-QED architectures. Our methods exploit Stark shift based Q-switching,
and are ideally suited to solid-state integrated optical approaches to quantum
computing.Comment: 4 pages, 3 figures, minor revision
Precision characterisation of two-qubit Hamiltonians via entanglement mapping
We show that the general Heisenberg Hamiltonian with non-uniform couplings
can be characterised by mapping the entanglement it generates as a function of
time. Identification of the Hamiltonian in this way is possible as the
coefficients of each operator control the oscillation frequencies of the
entanglement function. The number of measurements required to achieve a given
precision in the Hamiltonian parameters is determined and an efficient
measurement strategy designed. We derive the relationship between the number of
measurements, the resulting precision and the ultimate discrete error
probability generated by a systematic mis-characterisation, when implementing
two-qubit gates for quantum computing.Comment: 6 Pages, 3 figure
Two-Body Random Ensembles: From Nuclear Spectra to Random Polynomials
The two-body random ensemble (TBRE) for a many-body bosonic theory is mapped
to a problem of random polynomials on the unit interval. In this way one can
understand the predominance of 0+ ground states, and analytic expressions can
be derived for distributions of lowest eigenvalues, energy gaps, density of
states and so forth. Recently studied nuclear spectroscopic properties are
addressed.Comment: 8 pages, 4 figures. To appear in Physical Review Letter
Relation of amino acid transport to sodium-ion concentration
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31964/1/0000006.pd
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