2,844 research outputs found
Error-resistant Single Qubit Gates with Trapped Ions
Coherent operations constitutive for the implementation of single and
multi-qubit quantum gates with trapped ions are demonstrated that are robust
against variations in experimental parameters and intrinsically indeterministic
system parameters. In particular, pulses developed using optimal control theory
are demonstrated for the first time with trapped ions. Their performance as a
function of error parameters is systematically investigated and compared to
composite pulses.Comment: 5 pages 5 figure
Integrable dynamics of a discrete curve and the Ablowitz-Ladik hierarchy
We show that the following elementary geometric properties of the motion of a
discrete (i.e. piecewise linear) curve select the integrable dynamics of the
Ablowitz-Ladik hierarchy of evolution equations: i) the set of points
describing the discrete curve lie on the sphere S^3, ii) the distance between
any two subsequant points does not vary in time, iii) the dynamics does not
depend explicitly on the radius of the sphere. These results generalize to a
discrete context our previous work on continuous curves.Comment: LaTeX file, 14 pages + 4 figure
Modeling of diffusion of injected electron spins in spin-orbit coupled microchannels
We report on a theoretical study of spin dynamics of an ensemble of
spin-polarized electrons injected in a diffusive microchannel with linear
Rashba and Dresselhaus spin-orbit coupling. We explore the dependence of the
spin-precession and spin-diffusion lengths on the strengths of spin-orbit
interaction and external magnetic fields, microchannel width, and orientation.
Our results are based on numerical Monte Carlo simulations and on approximate
analytical formulas, both treating the spin dynamics quantum-mechanically. We
conclude that spin-diffusion lengths comparable or larger than the
precession-length occur i) in the vicinity of the persistent spin helix regime
for arbitrary channel width, and ii) in channels of similar or smaller width
than the precession length, independent of the ratio of Rashba and Dresselhaus
fields. For similar strengths of the Rashba and Dresselhaus fields, the
steady-state spin-density oscillates or remains constant along the channel for
channels parallel to the in-plane diagonal crystal directions. An oscillatory
spin-polarization pattern tilted by 45 with respect to the channel
axis is predicted for channels along the main cubic crystal directions. For
typical experimental system parameters, magnetic fields of the order of Tesla
are required to affect the spin-diffusion and spin-precession lengths.Comment: Replaced with final version (some explanations and figures improved).
8 pages, 6 figure
- âŠ