22,918 research outputs found
Circuit QED and sudden phase switching in a superconducting qubit array
Superconducting qubits connected in an array can form quantum many-body
systems such as the quantum Ising model. By coupling the qubits to a
superconducting resonator, the combined system forms a circuit QED system.
Here, we study the nonlinear behavior in the many-body state of the qubit array
using a semiclassical approach. We show that sudden switchings as well as a
bistable regime between the ferromagnetic phase and the paramagnetic phase can
be observed in the qubit array. A superconducting circuit to implement this
system is presented with realistic parameters .Comment: 4 pages, 3 figures, submitted for publication
On the Treves theorem for the AKNS equation
According to a theorem of Treves, the conserved functionals of the AKNS
equation vanish on all pairs of formal Laurent series of a specified form, both
of them with a pole of the first order. We propose a new and very simple proof
for this statement, based on the theory of B\"acklund transformations; using
the same method, we prove that the AKNS conserved functionals vanish on other
pairs of Laurent series. The spirit is the same of our previous paper on the
Treves theorem for the KdV, with some non trivial technical differences.Comment: LaTeX, 16 page
Cosmological implications of dwarf spheroidal chemical evolution
The chemical properties of dwarf spheroidals in the local group are shown to
be inconsistent with star formation being truncated after the reionization
epoch (z~8). Enhanced levels of [Ba/Y] in stars in dwarf spheroidals like
Sculptor indicate strong s-process production from low-mass stars whose
lifetimes are comparable with the duration of the pre-reionization epoch. The
chemical evolution of Sculptor is followed using a model with SNeII and SNeIa
feedback and mass- and metallicity-dependent nucleosynthetic yields for
elements from H to Pb. We are unable to reproduce the Ba/Y ratio unless stars
formed over an interval long enough for the low-mass stars to pollute the
interstellar medium with s-elements. This robust result challenges the
suggestion that most of the local group dwarf spheroidals are fossils of
reionization and supports the case for large initial dark matter halos.Comment: 7 pages, 4 figures. Accepted for publication in ApJ. Minor changes
following referee repor
Deterministic Generation of Entangled Photons in Superconducting Resonator Arrays
We present a scheme for the deterministic generation of entangled photon
pairs in a superconducting resonator array. The resonators form a
Jaynes-Cummings lattice via the coupling to superconducting qubits, and the
Kerr-like nonlinearity arises due to the coupling.We show that entangled
photons can be generated on demand by applying spectroscopic techniques and
exploiting the nonlinearity and symmetry in the resonators. The scheme is
robust against small parameter spreads due to fabrication errors. Our findings
can be used as a key element for quantum information processing in
superconducting quantum circuits.Comment: 4 pages, 3 figure
Microstructure and Fe-vacancy ordering in the KFexSe2 superconducting system
Structural investigations by means of transmission electron microscopy (TEM)
on KFexSe2 with 1.5 \leq x \leq 1.8 have revealed a rich variety of
microstructure phenomena, the KFe1.5Se2 crystal often shows a superstructure
modulation along the [310] zone-axis direction, this superstructure can be well
interpreted by the Fe-vacancy order within the a-b plane. Increase of
Fe-concentration in the KFexSe2 materials could not only result in the
appearance of superconductivity but also yield clear alternations of
microstructure. Structural inhomogeneity, the complex superstructures and
defect structures in the superconducting KFe1.8Se2 sample have been
investigated based on the high-resolution TEM.Comment: 13 pages, 4 figure
Two-qubit Quantum Logic Gate in Molecular Magnets
We proposed a scheme to realize a controlled-NOT quantum logic gate in a
dimer of exchange coupled single-molecule magnets, . We
chosen the ground state and the three low-lying excited states of a dimer in a
finite longitudinal magnetic field as the quantum computing bases and
introduced a pulsed transverse magnetic field with a special frequency. The
pulsed transverse magnetic field induces the transitions between the quantum
computing bases so as to realize a controlled-NOT quantum logic gate. The
transition rates between the quantum computing bases and between the quantum
computing bases and other excited states are evaluated and analyzed.Comment: 7 pages, 2 figure
Flat bidifferential ideals and semihamiltonian PDEs
In this paper we consider a class of semihamiltonian systems characterized by
the existence of a special conservation law.
The density and the current of this conservation law satisfy a second order
system of PDEs which has a natural interpretation in the theory of flat
bifferential ideals. The class of systems we consider contains important
well-known examples of semihamiltonian systems. Other examples, like genus 1
Whitham modulation equations for KdV, are related to this class by a
reciprocal trasformation.Comment: 18 pages. v5: formula (36) corrected; minor change
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