54,339 research outputs found
What we can learn from magnetic Compton scattering : application to the determination of spin polarization
Studies of spin-resolved electron momentum densities involve the measurement of the so-called magnetic Compton profile. This is a one-dimensional projection of the electron momentum distribution of only those electrons that contribute to the spin moment of a sample. The technique is applicable to ferri- and ferromagnetic materials. The profile is obtained via the inelastic 'Compton' scattering of high energy X-rays. Since electrons originating from different atomic orbitals have specific momentum densities, it is often possible to determine the origin of the magnetism present. Typically, interpretation requires the use of electronic structure calculations using molecular orbital and band structure approaches. Here, we highlight the application of the technique to the determination of the Fermi level spin polarization, the knowledge of which is important to the development of novel spintronic materials
Towards topological quantum computer
One of the principal obstacles on the way to quantum computers is the lack of
distinguished basis in the space of unitary evolutions and thus the lack of the
commonly accepted set of basic operations (universal gates). A natural choice,
however, is at hand: it is provided by the quantum R-matrices, the entangling
deformations of non-entangling (classical) permutations, distinguished from the
points of view of group theory, integrable systems and modern theory of
non-perturbative calculations in quantum field and string theory. Observables
in this case are (square modules of) the knot polynomials, and their pronounced
integrality properties could provide a key to error correction. We suggest to
use R-matrices acting in the space of irreducible representations, which are
unitary for the real-valued couplings in Chern-Simons theory, to build a
topological version of quantum computing.Comment: 14 page
Phase stability, ordering tendencies, and magnetism in single-phase fcc Au-Fe nanoalloys
Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but
L1 and L1 orderings were reported in single-phase Au-Fe nanoparticles.
Motivated by these observations, we study the structural and ordering
energetics in this alloy by combining density functional theory (DFT)
calculations with effective Hamiltonian techniques: a cluster expansion with
structural filters, and the configuration-dependent lattice deformation model.
The phase separation tendency in Au-Fe persists even if the fcc-bcc
decomposition is suppressed. The relative stability of disordered bcc and fcc
phases observed in nanoparticles is reproduced, but the fully ordered L1
AuFe, L1 AuFe, and L1 AuFe structures are unstable in DFT.
However, a tendency to form concentration waves at the corresponding [001]
ordering vector is revealed in nearly-random alloys in a certain range of
concentrations. This incipient ordering requires enrichment by Fe relative to
the equiatomic composition, which may occur in the core of a nanoparticle due
to the segregation of Au to the surface. Effects of magnetism on the chemical
ordering are also discussed.Comment: 23 pages, 11 figure
Controlled and combined remote implementations of partially unknown quantum operations of multiqubits using GHZ states
We propose and prove protocols of controlled and combined remote
implementations of partially unknown quantum operations belonging to the
restricted sets [An Min Wang: PRA, \textbf{74}, 032317(2006)] using GHZ states.
We detailedly describe the protocols in the cases of one qubit, respectively,
with one controller and with two senders. Then we extend the protocols to the
cases of multiqubits with many controllers and two senders. Because our
protocols have to demand the controller(s)'s startup and authorization or two
senders together working and cooperations, the controlled and combined remote
implementations of quantum operations definitely can enhance the security of
remote quantum information processing and potentially have more applications.
Moreover, our protocol with two senders is helpful to farthest arrive at the
power of remote implementations of quantum operations in theory since the
different senders perhaps have different operational resources and different
operational rights in practice.Comment: 26 pages, the submitted versio
production off the proton in a Regge-plus-chiral quark approach
A chiral constituent quark model approach, embodying s- and u-channel
exchanges,complemented with a Reggeized treatment for t-channel is presented. A
model is obtained allowing data for and to be describe satisfactorily. For the latter reaction, recently released
data by CLAS and CBELSA/TAPS Collaborations in the system total energy range
GeV are well reproduced due to the inclusion of
Reggeized trajectories instead of simple and poles.
Contribution from "missing" resonances is found to be negligible in the
considered processes.Comment: 23 pages.4 figures,4 tables, to appear in Phys.Rev.
Observation of sub-Poisson photon statistics in the cavity-QED microlaser
We have measured the second-order correlation function of the cavity-QED
microlaser output and observed a transition from photon bunching to
antibunching with increasing average number of intracavity atoms. The observed
correlation times and the transition from super- to sub-Poisson photon
statistics can be well described by gain-loss feedback or enhanced/reduced
restoring action against fluctuations in photon number in the context of a
quantum microlaser theory and a photon rate equation picture. However, the
theory predicts a degree of antibunching several times larger than that
observed, which may indicate the inadequacy of its treatment of atomic velocity
distributions.Comment: 4 pages, 4 figure
Strong decays of in an extended chiral quark model
The strong decays of the resonance are investigated in an
extended chiral quark model by including the low-lying components
in addition to the component. The results show that these five-quark
components in contribute significantly to the and decays. The contributions to the decay
come from both the lowest energy and the next-to-lowest energy five-quarks
components, while the contributions to the decay come from only the
latter one. Taking these contributions into account, the description for the
strong decays of is improved, especially, for the puzzling large
ratio of the decays to and .Comment: 6 pages, 1 figur
- …