31 research outputs found
Phonon-induced decoherence and dissipation in donor-based charge qubits
We investigate the phonon-induced decoherence and dissipation in a
donor-based charge quantum bit realized by the orbital states of an electron
shared by two dopant ions which are implanted in a silicon host crystal. The
dopant ions are taken from the group-V elements Bi, As, P, Sb. The excess
electron is coupled to deformation potential acoustic phonons which dominate in
the Si host. The particular geometry tailors a non-monotonous frequency
distribution of the phonon modes. We determine the exact qubit dynamics under
the influence of the phonons by employing the numerically exact quasi-adiabatic
propagator path integral scheme thereby taking into account all bath-induced
correlations. In particular, we have improved the scheme by completely
eliminating the Trotter discretization error by a Hirsch-Fye extrapolation. By
comparing the exact results to those of a Born-Markov approximation we find
that the latter yields appropriate estimates for the decoherence and relaxation
rates. However, noticeable quantitative corrections due to non-Markovian
contributions appear.Comment: 8 pages, 8 figures, published online in Eur.Phys.J.B, article in
press; the original publication is avaiable at www.eurphysj.or
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure
Magnetic Field and Force Calculations for ATLAS Asymmetrical Structure
Magnetic field distortion in the assymetrical ATLAS structure are calculated. Magnetic forces in the system are estimated. 3D magnetic field simulation by the Opera3D code for symmetrical and asymmetrical systems is used
Mermaid 3D code in ATLAS applications
The paper describes the new periodic boundary condition model of ATLAS detector and changes in the Mermaid 3D code algorithms necessary to calculate it. The parallel processing modification of the Mermaid code to perform the complete Atlas model calculation is presented in comparison with this 1:10 model of the fine TileCal structure