8,173 research outputs found
Cross-talk compensation of hyperfine control in donor qubit architectures
We theoretically investigate cross-talk in hyperfine gate control of
donor-qubit quantum computer architectures, in particular the Kane proposal. By
numerically solving the Poisson and Schr\"{o}dinger equations for the gated
donor system, we calculate the change in hyperfine coupling and thus the error
in spin-rotation for the donor nuclear-electron spin system, as the gate-donor
distance is varied. We thus determine the effect of cross-talk - the
inadvertent effect on non-target neighbouring qubits - which occurs due to
closeness of the control gates (20-30nm). The use of compensation protocols is
investigated, whereby the extent of crosstalk is limited by the application of
compensation bias to a series of gates. In light of these factors the
architectural implications are then considered.Comment: 15 pages, 22 figures, submitted to Nanotechnolog
Reducing Residual-Mass Effects for Domain-Wall Fermions
It has been suggested to project out a number of low-lying eigenvalues of the
four-dimensional Wilson--Dirac operator that generates the transfer matrix of
domain-wall fermions in order to improve simulations with domain-wall fermions.
We investigate how this projection method reduces the residual chiral
symmetry-breaking effects for a finite extent of the extra dimension. We use
the standard Wilson as well as the renormalization--group--improved gauge
action. In both cases we find a substantially reduced residual mass when the
projection method is employed. In addition, the large fluctuations in this
quantity disappear.Comment: 18 pages, 10 figures, references updated, comments adde
Multiple Stellar Populations in the Globular Cluster omega Centauri as Tracers of a Merger Event
The discovery of the Sagittarius dwarf galaxy, which is being tidally
disrupted by and merging with the Milky Way, supports the view that the halo of
the Galaxy has been built up at least partially by the accretion of similar
dwarf systems. The Sagittarius dwarf contains several distinct populations of
stars, and includes M54 as its nucleus, which is the second most massive
globular cluster associated with the Milky Way. The most massive globular
cluster is omega Centauri, and here we report that omega Centauri also has
several distinct stellar populations, as traced by red-giant-branch stars. The
most metal-rich red-giant-branch stars are about 2 Gyr younger than the
dominant metal-poor component, indicating that omega Centauri was enriched over
this timescale. The presence of more than one epoch of star formation in a
globular cluster is quite surprising, and suggests that omega Centauri was once
part of a more massive system that merged with the Milky Way, as the
Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were
much more frequent in the early history of the Galaxy and omega Centauri
appears to be a relict of this era.Comment: 7 pages, 3 figures, Latex+nature.sty (included), To appear in
November 4th issue of Natur
The states of W-class as shared resources for perfect teleportation and superdense coding
As we know, the states of triqubit systems have two important classes:
GHZ-class and W-class.
In this paper, the states of W-class are considered for teleportation and
superdense coding, and are generalized to multi-particle systems. First we
describe two transformations of the shared resources for teleportation and
superdense coding, which allow many new protocols from some known ones for
that. As an application of these transformations, we obtain a sufficient and
necessary condition for a state of W-class being suitable for perfect
teleportation and superdense coding. As another application, we find that state
can be used to
transmit three classical bits by sending two qubits, which was considered to be
impossible by P. Agrawal and A. Pati [Phys. Rev. A to be published]. We
generalize the states of W-class to multi-qubit systems and multi-particle
systems with higher dimension. We propose two protocols for teleportation and
superdense coding by using W-states of multi-qubit systems that generalize the
protocols by using proposed by P. Agrawal and A. Pati. We obtain an
optimal way to partition some W-states of multi-qubit systems into two
subsystems, such that the entanglement between them achieves maximum value.Comment: 10 pages, critical comments and suggestions are welcom
Optical study on doped polyaniline composite films
Localization driven by disorder has a strong influence on the conducting
property of conducting polymer. A class of authors hold the opinion that
disorder in the material is homogeneous and conducting polymer is disordered
metal close to Anderson-Mott Metal-Insulator transition, while others treat the
disorder as inhomogeneous and have the conclusion that conducting polymer is a
composite of ordered metallic regions and disordered insulating regions. The
morphology of conducting polymers is an important factor that have influence on
the type and extent of disorder. Different protonic acids used as dopants and
moisture have affection on polymer chain arrangement and interchain
interactions. A PANI-CSA film, two PANI-CSA/PANI-DBSA composite films with
different dopants ratio, and one of the composite films with different moisture
content are studied. Absolute reflectivity measurements are performed on the
films. Optical conductivity and the real part of dielectric function are
calculated by Kramers-Kronig(KK) relations. and
derivate from simple Drude model in low frequency range
and tendencies of the three sample are different and non-monotonic. The
Localization Modified Drude model(LMD) in the framework of Anderson-Mott theory
can not give a good fit to the experimental data. By introducing a distribution
of relaxation time into LMD, reasonable fits for all three samples are
obtained. This result supports the inhomogeneous picture.Comment: 6 figures, 7 page
Quantum teleportation via a W state
We investigate two schemes of the quantum teleportation with a state,
which belongs to a different class from a Greenberger-Horne-Zeilinger class. In
the first scheme, the state is shared by three parties one of whom, called
a sender, performs a Bell measurement. It is shown that quantum information of
an unknown state is split between two parties and recovered with a certain
probability. In the second scheme, a sender takes two particles of the
state and performs positive operator valued measurements in two ways. For two
schemes, we calculate the success probability and the average fidelity. We show
that the average fidelity of the second scheme cannot exceed that of the first
one.Comment: 7 pages, 1 figur
Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with NaI(Tl) crystal Detectors
Limits on the cross section for weakly interacting massive particles (WIMPs)
scattering off nucleons in the NaI(Tl) detectors at the Yangyang Underground
Laboratory are obtained with a 2967.4 kg*day data exposure. Nuclei recoiling
are identified by the pulse shape of scintillating photon signals. Data are
consistent with no nuclear recoil hypothesis, and 90% confidence level upper
limits are set. These limits partially exclude the DAMA/LIBRA region of
WIMP-sodium interaction with the same NaI(Tl) target detector. This 90%
confidence level upper limit on WIMP-nucleon spin-independent cross section is
3.26*10^-4 pb for a WIMP mass at 10 GeV/c^2
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