2,929 research outputs found
Entanglement of hard-core bose gas in degenerate levels under local noise
Quantum entanglement properties of the pseudo-spin representation of the BCS model is investigated. In case of degenerate energy levels, where wave functions take a particularly simple form, spontaneous breaking of exchange symmetry under local noise is studied. Even if the Hamiltonian has the same symmetry, it is shown that there is a non-zero probability to end up with a non-symmetric final state. For small systems, total probability for symmetry breaking is found to be inversely proportional to the system size
Quantum phase in nanoscopic superconductors
Using the pseudospin representation and the SU(2) phase operators we introduce a complex parameter to characterize both infinite and finite superconducting systems.While in the bulk limit the parameter becomes identical to the conventional order parameter, in the nanoscopic limit its modulus reduces to the number parity effect parameter and its phase takes discrete values. We evaluate the Josephson coupling energy and show that in bulk superconductor it reproduces the conventional expression and in the nanoscopic limit it leads to quantized Josephson effect. Finally, we study the phase flow or dual Josephson effect in a superconductor with fixed number of electrons
Quantum Phase in Nanoscopic Superconductors
Using the pseudospin representation and the SU(2) phase operators we
introduce a complex parameter to characterize both infinite and finite
superconducting systems. While in the bulk limit the parameter becomes
identical to the conventional order parameter, in the nanoscopic limit its
modulus reduces to the number parity effect parameter and its phase takes
discrete values. We evaluate the Josephson coupling energy and show that in
bulk superconductor it reproduces the conventional expression and in the
nanoscopic limit it leads to quantized Josephson effect. Finally, we study the
phase flow or dual Josephson effect in a superconductor with fixed number of
electrons.Comment: 11 page
Multiplicative and additive methods for the decomposition of the migration rates to/from Tokyo ma., 1985-90
My reserch will be about building and empirically testing the model exlaining the net migration to/from the Tokyo Metropolitan Area during 1985-90. This will be interms of interplay of three factors. Firstly, the effects of the "national economic vitality" will be considered. Various studies indicate that not only the national mobility rates, but also the mobility rates to/from the largest metropolitan areas are very sensitive to the changes in the national economy. Secondly, I would like to test the effects of the inter-prefectural disparities between Tokyo M.A. and other prefectures in terms of (mainly): per capita incomes, the differences in the economic structure, supply of higher education. Thirdly, I would like to test the effects of "demographic" factors which will be briefly the age structure of the population and the age-specific mobility rates, and thus the consequent supply of the potential in- and out-migrants to/from the Tokyo M.A. The study of experience of Japan, with very high level of urbanization, with give very valuable and necessary insights to countries with lower level of urbanization in order for them to plan and predict the growth of their largest cities in future.
Energy spectrum for two-dimensional potentials in very high magnetic fields
A method, analogous to supersymmetry transformation in quantum mechanics, is
developed for a particle in the lowest Landau level moving in an arbitrary
potential. The method is applied to two-dimensional potentials formed by Dirac
delta scattering centers. In the periodic case, the problem is solved exactly
for rational values of the magnetic flux (in units of flux quantum) per unit
cell. The spectrum is found to be self-similar, resembling the Hofstadter
butterfly.Comment: 9 pages, 3 figures, REVTEX, to appear in Phys. Rev. B, Sep. 1
Suppression of superconductivity in high- cuprates due to nonmagnetic impurities: Implications for the order parameter symmetry
We studied the effects of nonmagnetic impurities on high-temperature
superconductors by solving the Bogoliubov-de Gennes equations on a
two-dimensional lattice via exact diagonalization technique in a fully
self-consistent way. We found that s-wave order parameter is almost unaffected
by impurities at low concentrations while -wave order parameter
exhibits a strong linear decrease with impurity concentration. We evaluated the
critical impurity concentration at which superconductivity ceases to be
0.1 which is in good agreement with experimental values. We also investigated
how the orthorhombic nature of the crystal structure affects the suppression of
superconductivity and found that anisotropy induces an additional s-wave
component. Our results support -wave symmetry for tetragonal and
-wave symmetry for orthorhombic structure.Comment: LaTeX, 5 pages, 4 figures, uses grafik.sty (included
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