25,672 research outputs found
Robust Quantum State Transfer in Random Unpolarized Spin Chains
We propose and analyze a new approach for quantum state transfer between
remote spin qubits. Specifically, we demonstrate that coherent quantum coupling
between remote qubits can be achieved via certain classes of random,
unpolarized (infinite temperature) spin chains. Our method is robust to
coupling strength disorder and does not require manipulation or control over
individual spins. In principle, it can be used to attain perfect state transfer
over arbitrarily long range via purely Hamiltonian evolution and may be
particularly applicable in a solid-state quantum information processor. As an
example, we demonstrate that it can be used to attain strong coherent coupling
between Nitrogen-Vacancy centers separated by micrometer distances at room
temperature. Realistic imperfections and decoherence effects are analyzed.Comment: 4 pages, 2 figures. V2: Modified discussion of disorder, added
references - final version as published in Phys. Rev. Let
Quintessence Model and Observational Constraints
The recent observations of type Ia supernovae strongly support that the
universe is accelerating now and decelerated in the recent past. By assuming a
general relation between the quintessence potential and the quintessence
kinetic energy, a general relation is found between the quintessence energy
density and the scale factor. The potential includes both the hyperbolic and
the double exponential potentials. A detailed analysis of the transition from
the deceleration phase to the acceleration phase is then performed. We show
that the current constraints on the transition time, the equation of state and
the energy density of the quintessence field are satisfied in the model.Comment: update references,add acknowledgements and correct some errors,
accepted for publication in class. and quant. gra
A finite element boundary integral formulation for radiation and scattering by cavity antennas using tetrahedral elements
A hybrid finite element boundary integral formulation is developed using tetrahedral and/or triangular elements for discretizing the cavity and/or aperture of microstrip antenna arrays. The tetrahedral elements with edge based linear expansion functions are chosen for modeling the volume region and triangular elements are used for discretizing the aperture. The edge based expansion functions are divergenceless thus removing the requirement to introduce a penalty term and the tetrahedral elements permit greater geometrical adaptability than the rectangular bricks. The underlying theory and resulting expressions are discussed in detail together with some numerical scattering examples for comparison and demonstration
Temperature driven structural phase transition for trapped ions and its experimental detection
A Wigner crystal formed with trapped ion can undergo structural phase
transition, which is determined only by the mechanical conditions on a
classical level. Instead of this classical result, we show that through
consideration of quantum and thermal fluctuation, a structural phase transition
can be solely driven by change of the system's temperature. We determine a
finite-temperature phase diagram for trapped ions using the renormalization
group method and the path integral formalism, and propose an experimental
scheme to observe the predicted temperature-driven structural phase transition,
which is well within the reach of the current ion trap technology.Comment: 4 pages, 5 figure
The Pseudoscalar Meson and Heavy Vector Meson Scattering Lengths
We have systematically studied the S-wave pseudoscalar meson and heavy vector
meson scattering lengths to the third order with the chiral perturbation
theory, which will be helpful to reveal their strong interaction. For
comparison, we have presented the numerical results of the scattering lengths
(1) in the framework of the heavy meson chiral perturbation theory and (2) in
the framework of the infrared regularization. The chiral expansion converges
well in some channels.Comment: 10 pages, 1 figures, 4 tables. Corrected typos, Improved numerical
results, and More dicussions. Accepted for publication by Phys.Rev.
2*2 random matrix ensembles with reduced symmetry: From Hermitian to PT-symmetric matrices
A possibly fruitful extension of conventional random matrix ensembles is
proposed by imposing symmetry constraints on conventional Hermitian matrices or
parity-time- (PT-) symmetric matrices. To illustrate the main idea, we first
study 2*2 complex Hermitian matrix ensembles with O(2) invariant constraints,
yielding novel level-spacing statistics such as singular distributions,
half-Gaussian distribution, distributions interpolating between GOE (Gaussian
Orthogonal Ensemble) distribution and half Gaussian distributions, as well as
gapped-GOE distribution. Such a symmetry-reduction strategy is then used to
explore 2*2 PT-symmetric matrix ensembles with real eigenvalues. In particular,
PT-symmetric random matrix ensembles with U(2) invariance can be constructed,
with the conventional complex Hermitian random matrix ensemble being a special
case. In two examples of PT-symmetric random matrix ensembles, the
level-spacing distributions are found to be the standard GUE (Gaussian Unitary
Ensemble) statistics or "truncated-GUE" statistics
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