527 research outputs found
Resonance- and Chaos-Assisted Tunneling
We consider dynamical tunneling between two symmetry-related regular islands
that are separated in phase space by a chaotic sea. Such tunneling processes
are dominantly governed by nonlinear resonances, which induce a coupling
mechanism between ``regular'' quantum states within and ``chaotic'' states
outside the islands. By means of a random matrix ansatz for the chaotic part of
the Hamiltonian, one can show that the corresponding coupling matrix element
directly determines the level splitting between the symmetric and the
antisymmetric eigenstates of the pair of islands. We show in detail how this
matrix element can be expressed in terms of elementary classical quantities
that are associated with the resonance. The validity of this theory is
demonstrated with the kicked Harper model.Comment: 25 pages, 5 figure
Resonance Tunneling in Double-Well Billiards with a Pointlike Scatterer
The coherent tunneling phenomenon is investigated in rectangular billiards
divided into two domains by a classically unclimbable potential barrier. We
show that by placing a pointlike scatterer inside the billiard, we can control
the occurrence and the rate of the resonance tunneling. The key role of the
avoided crossing is stressed.
Keywords: chaotic tunneling, quantum billiard, delta potential, diabolical
degeneracy PACS: 3.65.-w, 4.30.Nk, 5.45.+b, 73.40.GkComment: Five pages ReVTEX, two column format with epsf figure
Stress Responses in Tropical Sparrows: Comparing Tropical and Temperate Zonotrichia
Seasonal modulation of the adrenocortical response appears to be ubiquitous in mid- to high- latitude vertebrates but has not been investigated in tropical vertebrates. Previous studies demonstrate that temperate passerines show seasonality in corticosterone secretion and corticosteroid binding globulin capacities. We examined seasonal and sex differences in the stress response in an equatorial population of Zonotrichia capensis, the only Zonotrichia that breeds in the tropics, and compared the results with those of northern Zonotrichia. Seasonal differences in tropical Zonotrichia would presumably be independent of photoperiod and thus directly related to such activities as reproduction and feather molt. In addition, we investigated the possible role of binding globulin as a sex steroid binding globulin, as suggested for temperate passerines. Similar to northern congeners, Z. capensis show seasonal modulation in total corticosterone and binding globulin capacity with higher levels during breeding than molt. However, unlike many temperate passerines, there are no sex differences in corticosterone secretion or binding globulin capacity. Furthermore, the seasonal differences in total corticosterone diminish when the free levels are calculated. The contrast between equatorial and northern congeners indicates factors such as breeding environment and life-history strategy may play important roles in shaping stress response in these species
Resonance-assisted tunneling in near-integrable systems
Dynamical tunneling between symmetry related invariant tori is studied in the
near-integrable regime. Using the kicked Harper model as an illustration, we
show that the exponential decay of the wave functions in the classically
forbidden region is modified due to coupling processes that are mediated by
classical resonances. This mechanism leads to a substantial deviation of the
splitting between quasi-degenerate eigenvalues from the purely exponential
decrease with 1 / hbar obtained for the integrable system. A simple
semiclassical framework, which takes into account the effect of the resonance
substructure on the KAM tori, allows to quantitatively reproduce the behavior
of the eigenvalue splittings.Comment: 4 pages, 2 figures, gzipped tar file, to appear in Phys. Rev. Lett,
text slightly condensed compared to first versio
Semiclassical transmission across transition states
It is shown that the probability of quantum-mechanical transmission across a
phase space bottleneck can be compactly approximated using an operator derived
from a complex Poincar\'e return map. This result uniformly incorporates
tunnelling effects with classically-allowed transmission and generalises a
result previously derived for a classically small region of phase space.Comment: To appear in Nonlinearit
Scarring Effects on Tunneling in Chaotic Double-Well Potentials
The connection between scarring and tunneling in chaotic double-well
potentials is studied in detail through the distribution of level splittings.
The mean level splitting is found to have oscillations as a function of energy,
as expected if scarring plays a role in determining the size of the splittings,
and the spacing between peaks is observed to be periodic of period
{} in action. Moreover, the size of the oscillations is directly
correlated with the strength of scarring. These results are interpreted within
the theoretical framework of Creagh and Whelan. The semiclassical limit and
finite-{} effects are discussed, and connections are made with reaction
rates and resonance widths in metastable wells.Comment: 22 pages, including 11 figure
Semiclassical Trace Formulas for Noninteracting Identical Particles
We extend the Gutzwiller trace formula to systems of noninteracting identical
particles. The standard relation for isolated orbits does not apply since the
energy of each particle is separately conserved causing the periodic orbits to
occur in continuous families. The identical nature of the particles also
introduces discrete permutational symmetries. We exploit the formalism of
Creagh and Littlejohn [Phys. Rev. A 44, 836 (1991)], who have studied
semiclassical dynamics in the presence of continuous symmetries, to derive
many-body trace formulas for the full and symmetry-reduced densities of states.
Numerical studies of the three-particle cardioid billiard are used to
explicitly illustrate and test the results of the theory.Comment: 29 pages, 11 figures, submitted to PR
Semiclassical theory of spin-orbit interaction in the extended phase space
We consider the semiclassical theory in a joint phase space of spin and
orbital degrees of freedom. The method is developed from the path integrals
using the spin-coherent-state representation, and yields the trace formula for
the density of states. We discuss special cases, such as weak and strong
spin-orbit coupling, and relate the present theory to the earlier approaches.Comment: 36 pages, 8 figures. Version 2: revised Sec. 4.4 and Appendix B;
minor corrections elsewher
Near-field MIMO communication links
A procedure to achieve near-field multiple input multiple output (MIMO) communication with equally strong channels is demonstrated in this paper. This has applications in near-field wireless communications, such as Chip-to-Chip (C2C) communication or wireless links between printed circuit boards. Designing the architecture of these wireless C2C networks is, however, based on standard engineering design tools. To attain this goal, a network optimization procedure is proposed, which introduces decoupling and matching networks. As a demonstration, this optimization procedure is applied to a 2-by-2 MIMO with dipole antennas. The potential benefits and design trade-offs are discussed for implementation of wireless radio-frequency interconnects in chip-to-chip or device-to-device communication such as in an Internet-of-Things scenario
Instantons revisited: dynamical tunnelling and resonant tunnelling
Starting from trace formulae for the tunnelling splittings (or decay rates)
analytically continued in the complex time domain, we obtain explicit
semiclassical expansions in terms of complex trajectories that are selected
with appropriate complex-time paths. We show how this instanton-like approach,
which takes advantage of an incomplete Wick rotation, accurately reproduces
tunnelling effects not only in the usual double-well potential but also in
situations where a pure Wick rotation is insufficient, for instance dynamical
tunnelling or resonant tunnelling. Even though only one-dimensional autonomous
Hamiltonian systems are quantitatively studied, we discuss the relevance of our
method for multidimensional and/or chaotic tunnelling
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