1,472 research outputs found
Surface code architecture for donors and dots in silicon with imprecise and nonuniform qubit couplings
A scaled quantum computer with donor spins in silicon would benefit from a
viable semiconductor framework and a strong inherent decoupling of the qubits
from the noisy environment. Coupling neighbouring spins via the natural
exchange interaction according to current designs requires gate control
structures with extremely small length scales. We present a silicon
architecture where bismuth donors with long coherence times are coupled to
electrons that can shuttle between adjacent quantum dots, thus relaxing the
pitch requirements and allowing space between donors for classical control
devices. An adiabatic SWAP operation within each donor/dot pair solves the
scalability issues intrinsic to exchange-based two-qubit gates, as it does not
rely on sub-nanometer precision in donor placement and is robust against noise
in the control fields. We use this SWAP together with well established global
microwave Rabi pulses and parallel electron shuttling to construct a surface
code that needs minimal, feasible local control.Comment: Published version - more detailed discussions, robustness to
dephasing pointed out additionall
Rho meson decay width in SU(2) gauge theories with 2 fundamental flavours
7 pages, Proceedings of the 34th International Symposium on Lattice Field Theory (Lattice 2016)SU(2) gauge theories with two quark flavours in the fundamental representation are among the most promising theories of composite dynamics describing the electroweak sector. Three out of five Goldstone bosons in these models become the longitudinal components of the W and Z bosons giving them mass. Like in QCD, we expect a spectrum of excitations which appear as resonances in vector boson scattering, in particular the vector resonance corresponding to the rho-meson in QCD. In this talk I will present the preliminary results of the first calculation of the rho-meson decay width in this theory, which is analogous to rho to two pions decay calculation in QCD. The results presented were calculated in a moving frame with total momentum (0,0,1) on two ensembles. Future plans include using 3 moving frames on a larger set of ensembles to extract the resonance parameters more reliably and also take the chiral and continuum limits
Dynamics of drag and force distributions for projectile impact in a granular medium
Our experiments and molecular dynamics simulations on a projectile
penetrating a two-dimensional granular medium reveal that the mean deceleration
of the projectile is constant and proportional to the impact velocity. Thus,
the time taken for a projectile to decelerate to a stop is independent of its
impact velocity. The simulations show that the probability distribution
function of forces on grains is time-independent during a projectile's
penetration of the medium. At all times the force distribution function
decreases exponentially for large forces.Comment: 4 page
Higher representations on the lattice: numerical simulations. SU(2) with adjoint fermions
We discuss the lattice formulation of gauge theories with fermions in
arbitrary representations of the color group, and present in detail the
implementation of the HMC/RHMC algorithm for simulating dynamical fermions. We
discuss the validation of the implementation through an extensive set of tests,
and the stability of simulations by monitoring the distribution of the lowest
eigenvalue of the Wilson-Dirac operator. Working with two flavors of Wilson
fermions in the adjoint representation, benchmark results for realistic lattice
simulations are presented. Runs are performed on different lattice sizes
ranging from 4^3x8 to 24^3x64 sites. For the two smallest lattices we also
report the measured values of benchmark mesonic observables. These results can
be used as a baseline for rapid cross-checks of simulations in higher
representations. The results presented here are the first steps towards more
extensive investigations with controlled systematic errors, aiming at a
detailed understanding of the phase structure of these theories, and of their
viability as candidates for strong dynamics beyond the Standard model.Comment: 16 pages, 12 figures, 6 tables. Published versio
Chiral transition and deconfinement in N_f = 2 QCD
The transition is studied by means of a disorder parameter detecting
condensation of magnetic monopoles in the vacuum. The deconfining transition is
found to coincide with the chiral transition and the susceptibility \rho,
related to the disorder parameter, is consistent with a first order phase
transition.Comment: 3 pages, 2 figures. Poster presented at Lattice2004(topology),
Fermilab, June 21-26, 200
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