753 research outputs found
Quantum register based on structured diamond waveguide with NV centers
We propose a scheme of quantum information processing with NV-centers
embedded inside diamond nanostructure. Single NV-center placed in the cavity
plays role of an electron spin qubit which evolution is controlled by microwave
pulses. Besides, it couples to the cavity field via optical photon exchange. In
their turn, neighbor cavities are coupled to each other through the photon
hopping to form a bus waveguide mode. This waveguide mode overlaps with all
NV-centers. Entanglement between distant centers is organized by appropriate
tuning of their optical frequency relative to the waveguide frequency via
electrostatic control without lasers. We describe the controlled-Z operation
that is by one order of magnitude faster than in off-resonant laser-assisted
schemes proposed earlier. Spectral characteristics of the one-dimensional chain
of microdisks are calculated by means of numerical modeling, using the approach
analogous to the tight-binding approximation in the solid-state physics. The
data obtained allow to optimize the geometry of the microdisk array for the
effective implementation of quantum operations.Comment: to be published in Proc. of SPI
Comparison of radiative energy loss models in a hot QCD medium
The suppression of high hadron production in heavy ion collisions is
thought to be due to energy loss by gluon radiation off hard partons in a QCD
medium. Existing models of QCD radiative energy loss in a color-charged medium
give estimates of the coupling strength of the parton to the medium which
differ by a factor of . We will present a side-by-side comparison of two
different formalisms to calculate the energy loss of light quarks and gluons:
the multiple soft scattering approximation (ASW-MS) and the opacity expansion
formalism (ASW-SH and WHDG-rad). A common time-temperature profile is used to
characterize the medium. The results are compared to the single hadron
suppression at RHIC energies. In addition the influcence of
homogeneous and non-homogeneous distribution of scattering centers is
discussed. We find that using an equivalent brick overestimates the energy loss
for long parton trajectories.Comment: Proceedings Hard Probes 2010, October 10-15, Eilat (Israel
Addressing the Transition Needs of Youth with Disabilities through the WIA System
Interagency collaboration has been repeatedly cited as one of the most important strategies in helping youth with disabilities move successfully from school into employment and adult life. However, often the primary focus of the collaboration and planning between school personnel and community service providers has been on disability-specific services and not on other, more generically available programs and services.The passage of the Workforce Investment Act (WIA) of 1998 offers new options and opportunities for youth in transition. WIA has challenged communities to create opportunities for all youth that moved beyond traditional vocational rehabilitation and related services. WIA represents expanded opportunities to prepare youth with disabilities for the transition to employment by assuring both access to and participation in WIA-funded youth and adult services. These services may benefit youth with disabilities as they plan for and make the transition from school to work
Lyapunov exponent for a gas of soft scatterers
For a fast particle moving within a two-dimensional array of soft scatterers
- centers of weak and short-range potential - the dependence of the Lyapunov
exponent on the system parameters is studied. The use of the linearized
equations for variations of the propagation angles and impact parameters of
consequent collisions reduces the problem to that of calculation of the
Lyapunov exponent of an ensemble of strongly correlated random matrices with
given statistics of matrix elements. In the simplest approximation this
Lyapunov exponent is proportional to the interaction strength and inversely
proportional to the square root of the interaction range. The model
satisfactorily describes the intensity of chaos in a system of two weakly
interacting particles moving in a two-dimensional regular confining potential.Comment: 3 pages, 3 figure
Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe(AsP)
We present a comprehensive overview of vortex pinning in single crystals of
the isovalently substituted iron-based superconductor
BaFe(AsP), a material that qualifies as an
archetypical clean superconductor, containing only sparse strong point-like
pins [in the sense of C.J. van der Beek {\em et al.}, Phys. Rev. B {\bf 66},
024523 (2002)]. Widely varying critical current values for nominally similar
compositions show that flux pinning is of extrinsic origin. Vortex
configurations, imaged using the Bitter decoration method, show less density
fluctuations than those previously observed in charge-doped
Ba(FeCo)As single crystals. Analysis reveals that the
pinning force and -energy distributions depend on the P-content . However,
they are always much narrower than in Ba(FeCo)As, a
result that is attributed to the weaker temperature dependence of the
superfluid density on approaching in
BaFe(AsP). Critical current density measurements and
pinning force distributions independently yield a mean distance between
effective pinning centers nm, increasing with
increasing P-content . This evolution can be understood as being the
consequence of the P-dependence of the London penetration depth. Further
salient features are a wide vortex free "Meissner belt", observed at the edge
of overdoped crystals, and characteristic chain-like vortex arrangements,
observed at all levels of P-substitution.Comment: 11 page
Modified reaction centers from Rhodobacter sphaeroides R26
Incubation of photosynthetic reaction centers from Rhodobacter sphaeroides R26 with exogenous 132-OH-bacteriochlorophyll ap or aGG according to Scheer et al. (1987) results in the exchange of endogenous bacteriochlorophyll ap. The exchange amounts to less-than-or-equals, slant 50% according to HPLC analysis, corresponding to a complete replacement of the ‘monomeric’ bacteriochlorophylls, bm and bl, by exogenous pigment. The absorption spectra show small, but distinct changes in the Qx-region of the bacteriochlorophylls, and bleaching of the modified reaction centers is retained. The corresponding binding sites must be accessible from the exterior, and allow for the introduction of a polar residue at C-132. This is supported by the observation of side reactions of the endogenous ‘monomeric’ bacteriochlorophylls within the reaction center pigments, e.g. epimerization and hydroxylation at C-132
Energetics of the primary electron transfer reaction revealed by ultrafast spectroscopy on modified bacterial reaction centers
The modification of reaction centers from Rhodobacter sphaeroides by the introduction of pheophytins instead of bacteriopheophytins leads to interesting changes in the primary photosynthetic reaction: long-living populations of the excited electronic state of the special pair P* and the bacteriochlorophyll anion B−A show up. The data allow the determination of the energetics in the reaction center. The free energy of the first intermediate P+B−A, where the electron has reached the accessory bacteriochlorophyll BA lies ≈ 450 cm−1 below the initially excited special pair P*
Four-wave mixing, quantum control and compensating losses in doped negative-index photonic metamaterials
The possibility of compensating absorption in negative-index metatamterials
(NIMs) doped by resonant nonlinear-optical centers is shown. The role of
quantum interference and extraordinary properties of four-wave parametric
amplification of counter-propagating electromagnetic waves in NIMs are
discussed.Comment: 3 pages, 3 figures, LaTeX, corrected typos in eqs. (1) and (2
- …