64,320 research outputs found
Inconsistences in Interacting Agegraphic Dark Energy Models
It is found that the origin agegraphic dark energy tracks the matter in the
matter-dominated epoch and then the subsequent dark-energy-dominated epoch
becomes impossible. It is argued that the difficulty can be removed when the
interaction between the agegraphic dark energy and dark matter is considered.
In the note, by discussing three different interacting models, we find that the
difficulty still stands even in the interacting models. Furthermore, we find
that in the interacting models, there exists the other serious inconsistence
that the existence of the radiation/matter-dominated epoch contradicts the
ability of agegraphic dark energy in driving the accelerated expansion. The
contradiction can be avoided in one of the three models if some constraints on
the parameters hold.Comment: 12 pages, no figure; analysis is added; conclusion is unchange
Geometric Phase, Hannay's Angle, and an Exact Action Variable
Canonical structure of a generalized time-periodic harmonic oscillator is
studied by finding the exact action variable (invariant). Hannay's angle is
defined if closed curves of constant action variables return to the same curves
in phase space after a time evolution. The condition for the existence of
Hannay's angle turns out to be identical to that for the existence of a
complete set of (quasi)periodic wave functions. Hannay's angle is calculated,
and it is shown that Berry's relation of semiclassical origin on geometric
phase and Hannay's angle is exact for the cases considered.Comment: Submitted to Phys. Rev. Lett. (revised version
Coherent output of photons from coupled superconducting transmission line resonators controlled by charge qubits
We study the coherent control of microwave photons propagating in a
superconducting waveguide consisting of coupled transmission line resonators,
each of which is connected to a tunable charge qubit. While these coupled line
resonators form an artificial photonic crystal with an engineered photonic band
structure, the charge qubits collectively behave as spin waves in the low
excitation limit, which modify the band-gap structure to slow and stop the
microwave propagation. The conceptual exploration here suggests an
electromagnetically controlled quantum device based on the on-chip circuit QED
for the coherent manipulation of photons, such as the dynamic creation of
laser-like output from the waveguide by pumping the artificial atoms for
population inversion.Comment: 8 pages, 3 figure
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