5,664 research outputs found
Experimental demonstration of four-party quantum secret sharing
Secret sharing is a multiparty cryptographic task in which some secret
information is splitted into several pieces which are distributed among the
participants such that only an authorized set of participants can reconstruct
the original secret. Similar to quantum key distribution, in quantum secret
sharing, the secrecy of the shared information relies not on computational
assumptions, but on laws of quantum physics. Here, we present an experimental
demonstration of four-party quantum secret sharing via the resource of
four-photon entanglement
Spin-Gap Phase in the One-Dimensional t-J-J' Model
The spin-gap phase of the one-dimensional t-J-J' model is studied by the
level-crossing of the singlet and the triplet excitation spectra.
The phase boundary obtained between the Tomonaga-Luttinger and the spin-gap
phases is remarkably consistent with the analytical results at the
and the low-density limits discussed by Ogata et al.
The spin-gap phase has a single domain in the phase diagram even if the spin
gap opens at half-filling.
The phase boundary coincides with the line where the
Tomonaga-Luttinger liquid behaves as free electrons, in the low-density region.
The relation between our method and the solution of the two-electron problem
is also discussed.Comment: 4 pages(JPSJ.sty), 5 figures(EPS), to appear in J. Phys. Soc. Jpn.
67, No.3 (1998
Dissociation of Relativistic Projectiles with the Continuum-Discretized Coupled-Channels Method
Relativistic effects in the breakup of weakly-bound nuclei at intermediate
energies are studied by means of the continuum-discretized coupled-channels
method with eikonal approximation. Nuclear coupling potentials with Lorentz
contraction are newly included and those effects on breakup cross sections are
investigated. We show that relativistic corrections lead to larger breakup
cross sections. Coupled-channel effects on the breakup cross sections are also
discussed.Comment: 9 pages, 7 figures, to be published in Prog. Theo. Phy
Recent developments in the eikonal description of the breakup of exotic nuclei
The study of exotic nuclear structures, such as halo nuclei, is usually
performed through nuclear reactions. An accurate reaction model coupled to a
realistic description of the projectile is needed to correctly interpret
experimental data. In this contribution, we briefly summarise the assumptions
made within the modelling of reactions involving halo nuclei. We describe
briefly the Continuum-Discretised Coupled Channel method (CDCC) and the
Dynamical Eikonal Approximation (DEA) in particular and present a comparison
between them for the breakup of 15C on Pb at 68AMeV. We show the problem faced
by the models based on the eikonal approximation at low energy and detail a
correction that enables their extension down to lower beam energies. A new
reaction observable is also presented. It consists of the ratio between angular
distributions for two different processes, such as elastic scattering and
breakup. This ratio is completely independent of the reaction mechanism and
hence is more sensitive to the projectile structure than usual reaction
observables, which makes it a very powerful tool to study exotic structures far
from stability.Comment: Contribution to the proceedings of the XXI International School on
Nuclear Physics and Applications & the International Symposium on Exotic
Nuclei, dedicated to the 60th Anniversary of the JINR (Dubna) (Varna,
Bulgaria, 6-12 September 2015), 7 pages, 4 figure
Variational Study of the Spin-Gap Phase of the One-Dimensional t-J Model
We propose a correlated spin-singlet-pairs wave function to describe the
spin-gap phase of the one-dimensional model at low density. Adding a
Jastrow factor with a variational parameter, , first introduced by
Hellberg and Mele, is shown to correctly describe the long-range behavior
expected for the Luther-Emery phase. Using the variational Monte Carlo method
we establish a relation between and the Luttinger exponent ,
.Comment: 4 pages (LaTex), 3 figures attache
Is there spin-charge separation in the 2D Hubbard and t-J models at low electronic densities?
The spin and density correlation functions of the two-dimensional Hubbard
model at low electronic density are calculated in the ground state by
using the power method, and at finite temperatures by using the quantum Monte
Carlo technique. Both approaches produce similar results, which are in close
agreement with numerical and high temperature expansion results for the
two-dimensional model. Using perturbative approximations, we show
that the examination of the density correlation function alone is not enough to
support recent claims in the literature that suggested spin and charge
separation in the low electronic density regime of the model.Comment: 11 pages, tex, 3 figures upon request, NTHU - preprin
Luttinger Liquid Instability in the One Dimensional t-J Model
We study the t-J model in one dimension by numerically projecting the true
ground state from a Luttinger liquid trial wave function. We find the model
exhibits Luttinger liquid behavior for most of the phase diagram in which
interaction strength and density are varied. However at small densities and
high interaction strengths a new phase with a gap to spin excitations and
enhanced superconducting correlations is found. We show this phase is a
Luther-Emery liquid and study its correlation functions.Comment: REVTEX, 11 pages. 4 Figures available on request from
[email protected]
Superconductivity in a Quasi One Dimensional Spin Liquid
The single rung t-J ladder is analyzed in a mean field theory using
Gutzwiller renormalization of the matrix elements to account for strong
correlation. The spin liquid (RVB) state at half-filling evolves into a
superconducting state upon doping. The order parameter has a modified d-wave
character. A lattice of weakly coupled ladders should show a superconducting
phase transition.Comment: 9 pages + 4 postscript files appende
Possibility of f-wave spin-triplet superconductivity in the CoO superconductor: a case study on a 2D triangular lattice in the repulsive Hubbard model
Stimulated by the recent finding of NaCoO.1.3HO
superconductor, we investigate superconducting instabilities on a 2D triangular
lattice in the repulsive Hubbard model. Using the third-order perturbation
expansion with respect to the on-site repulsion , we evaluate the linearized
Dyson-Gor'kov equation. We find that an -wave spin-triplet pairing is the
most stable in a wide range of the next nearest neighbor hopping integral
and an electron number density . The introduction of is crucial to
adjust the van Hove singularities to the neighborhood of the Fermi surface
crossing around K point. In this case, the bare spin susceptibility shows the
broad peak around point. These conditions stabilize the -wave
pairing. Although the -wave pairing is also given by the
fluctuation-exchange approximation, the transition temperature is too low to be
observed. This is because the depairing effect by the spin fluctuation is
over-estimated. Thus, the third-order vertex corrections are important for the
spin-triplet superconductivity, like the case in SrRuO.Comment: 4 pages, 7 figure
The Phase Diagram of Correlated Electrons in a Lattice of Berry Molecules
A model for correlated electrons in a lattice with local additional spin--1
degrees of freedom inducing constrained hopping, is studied both in the low
density limit and at quarter filling. We show that in both 1D and 2D two
particles form a bound state even in presence of a repulsive U<U_c. A picture
of a dilute Bose gas, leading to off-diagonal long range order (LRO) in 2D
(quasi-LRO in 1D), is supported by quantitative calculations in 1D which allow
for a determination of the phase diagram.Comment: 7 pages + 2 ps figures, published versio
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