5,361 research outputs found
Exact quantum dynamics of XXZ central spin problems
We obtain analytically close forms of benchmark quantum dynamics of the
collapse and revival (CR), reduced density matrix, Von Neumann entropy, and
fidelity for the XXZ central spin problem. These quantities characterize the
quantum decoherence and entanglement of the system with few to many bath spins,
and for a short to infinitely long time evolution. For the homogeneous central
spin problem, the effective magnetic field , coupling constant and
longitudinal interaction significantly influence the time scales of
the quantum dynamics of the central spin and the bath, providing a tunable
resource for quantum metrology. Under the resonance condition , the
location of the -th revival peak in time reaches a simple relation for a large . For , and a
small polarization in the initial spin coherent state, our analytical result
for the CR recovers the known expression found in the Jaynes-Cummings model,
thus building up an exact dynamical connection between the central spin
problems and the light-matter interacting systems in quantum nonlinear optics.
In addition, the CR dynamics is robust to a moderate inhomogeneity of the
coupling amplitudes, while disappearing at strong inhomogeneity.Comment: added new result on inhomogeneous central spin problem and added new
references and supplementary material, 6 pages + 15 pages; 4 figures + 14
figure
Remarks on the Theory of Cosmological Perturbation
It is shown that the power spectrum defined in the Synchronous Gauge can not
be directly used to calculate the predictions of cosmological models on the
large-scale structure of universe, which should be calculated directly by a
suitable gauge-invariant power spectrum or the power spectrum defined in the
Newtonian Gauge.Comment: 13 pages, 1 figure, minor changes, to be published in Chinese Physics
Letter
(Benzoato-κO)bis(1,10-phenanthroline-κ2 N,N′)copper(II) chloride benzoic acid disolvate
In the title complex, [Cu(C7H5O2)(C12H8N2)2]Cl·2C6H5COOH, the CuII ion is coordinated by one carboxylate O atom from a benzoate anion and four N atoms from two phenantroline ligands in a distorted five-coordinate trigonal-bipyramidal CuON4 chromophore. The Cu2+ and the Cl− ion are imposed by a twofold rotation axiss which also bisects the equally disordered benzoate anion. In the crystal, the molecules are assembled into chains along [010] by C—H⋯Cl, O—H⋯Cl and C—H⋯O hydrogen-bonding interactions. The resulting chains are further connected into two-dimensional supramolecular layers parallel to [100] by interchain π⋯π stacking interactions [centroid–centroid distance = 3.823 (5) Å] between the phenanthroline ligands and the benzoic acid molecules, and by C—H⋯O hydrogen-bonding interactions. Strong π⋯π stacking interactions between adjacent phenantroline ligands [3.548 (4) Å] assemble the layers into a three-dimensional supramolecular architecture
Flemingia macrophylla Extract Ameliorates Experimental Osteoporosis in Ovariectomized Rats
Flemingia macrophylla (Leguminosae), a native plant of Taiwan, is used as folk medicine. An in vitro study showed that a 75% ethanolic extract of F. macrophylla (FME) inhibited osteoclast differentiation of cultured rat bone marrow cells, and the active component, lespedezaflavanone A (LDF-A), was isolated. It was found that oral administration of FME for 13 weeks suppressed bone loss in ovariectomized rats, an experimental model of osteoporosis. In addition, FME decreased urinary deoxypyridinoline concentrations but did not inhibit serum alkaline phosphatase activities, indicating that it ameliorated bone loss via inhibition of bone resorption. These results suggest that FME may represent a useful remedy for the treatment of bone resorption diseases, such as osteoporosis. In addition, LDF-A could be used as a marker compound to control the quality of FME
- …