68 research outputs found
The parity-violating asymmetry in the 3He(n,p)3H reaction
The longitudinal asymmetry induced by parity-violating (PV) components in the
nucleon-nucleon potential is studied in the charge-exchange reaction 3He(n,p)3H
at vanishing incident neutron energies. An expression for the PV observable is
derived in terms of T-matrix elements for transitions from the {2S+1}L_J=1S_0
and 3S_1 states in the incoming n-3He channel to states with J=0 and 1 in the
outgoing p-3H channel. The T-matrix elements involving PV transitions are
obtained in first-order perturbation theory in the hadronic weak-interaction
potential, while those connecting states of the same parity are derived from
solutions of the strong-interaction Hamiltonian with the
hyperspherical-harmonics method. The coupled-channel nature of the scattering
problem is fully accounted for. Results are obtained corresponding to realistic
or chiral two- and three-nucleon strong-interaction potentials in combination
with either the DDH or pionless EFT model for the weak-interaction potential.
The asymmetries, predicted with PV pion and vector-meson coupling constants
corresponding (essentially) to the DDH "best values" set, range from -9.44 to
-2.48 in units of 10^{-8}, depending on the input strong-interaction
Hamiltonian. This large model dependence is a consequence of cancellations
between long-range (pion) and short-range (vector-meson) contributions, and is
of course sensitive to the assumed values for the PV coupling constants.Comment: 19 pages, 15 tables, revtex
Comment on "Imaging the Local Density of States of Optical Corrals"
In a recent letter Chicanne {\em et al.} [1] reported the experimental
observation of the electromagnetic local density of states LDOS established by
gold nanostructures. The obtained images have been compared with combinations
of partial LDOSs defined in terms of the imaginary part of the Green-tensor
calculated at the tip position.
Moreover just this comparison was the criterion for the choice of the optimum
tip design. These results support the point of view that ( is the unit vector used to define the effective
dipole associated to the illuminating tip) is the key quantity to interpret
SNOM images in analogy with the electronic LDOS measured by the scanning
tunneling microscope (STM). Rigorous Green-tensor analysis shows that (that is also the key quantity determining spontaneous decay rates
of molecular transitions) is not the correct key quantity, and that
measurements in Ref. [1] should have been compared with a different quantity.
Moreover the identification of with the detected SNOM signal
can lead to unphysical results
Nonequilibrium Langevin Approach to Quantum Optics in Semiconductor Microcavities
Recently the possibility of generating nonclassical polariton states by means
of parametric scattering has been demonstrated. Excitonic polaritons propagate
in a complex interacting environment and contain real electronic excitations
subject to scattering events and noise affecting quantum coherence and
entanglement. Here we present a general theoretical framework for the realistic
investigation of polariton quantum correlations in the presence of coherent and
incoherent interaction processes. The proposed theoretical approach is based on
the {\em nonequilibrium quantum Langevin approach for open systems} applied to
interacting-electron complexes described within the dynamics controlled
truncation scheme. It provides an easy recipe to calculate multi-time
correlation functions which are key-quantities in quantum optics. As a first
application, we analyze the build-up of polariton parametric emission in
semiconductor microcavities including the influence of noise originating from
phonon induced scattering.Comment: some corrections in the presentation mad
Near-field light emission from semiconductor macroatoms
We present a microscopic theoretical analysis of time and spatially resolved photoluminescence of naturally occurring quantum dots induced by monolayer fluctuations in the thickness of semiconductor quantum wells. In particular we
study the carrier dynamics and the emission properties of a semiconductor quantum dot under both continuous-wave and pulsed excitations resonant with the barrier energy levels. We show that collection-mode near-field optical microscopy allows the detection of light emission from excitonic dark states. We find that, at low temperature, the second (dark) energy level displays a carrier density significantly larger
than that of the lowest energy level. This behaviour is a consequence of carrier trapping due to the symmetry-induced suppression of radiative recombination
Decoherence-Free Emergence of Macroscopic Local Realism for entangled photons in a cavity
We investigate the influence of environmental noise on polarization entangled
light generated by parametric emission in a cavity. By adopting a recently
developed separability criterion, we show that: i) self-stimulation may
suppress the detrimental influence of noise on entanglement; ii) when
self-stimulation becomes effective, a classical model of parametric emission
incorporating noise provides the same results of quantum theory for the
expectation values involved in the separability criterion. Moreover we show
that, in the macroscopic limit, it is impossible to observe violations of local
realism with measurements of -particle correlations, whatever n but finite.
These results provide an interesting example of the emergence of macroscopic
local realism in the presence of strong entanglement even in the absence of
decoherence.Comment: 1 figur
Dynamics-Controlled Truncation Scheme for Nonlinear Dynamics in Semiconductor Microcavities
We present a systematic theory of Coulomb-induced correlation effects in the
nonlinear optical processes within the strong-coupling regime. In this paper we
shall set a dynamics controlled truncation scheme \cite{Axt Stahl} microscopic
treatment of nonlinear parametric processes in SMCs including the
electromagnetic field quantization. It represents the starting point for the
microscopic approach to quantum optics experiments in the strong coupling
regime without any assumption on the quantum statistics of electronic
excitations (excitons) involved. We exploit a previous technique, used in the
semiclassical context, which, once applied to four-wave mixing in quantum
wells, allowed to understand a wide range of observed phenomena \cite{Sham
PRL95}. We end up with dynamical equations for exciton and photon operators
which extend the usual semiclassical description of Coulomb interaction
effects, in terms of a mean-field term plus a genuine non-instantaneous
four-particle correlation, to quantum optical effects.Comment: preprint version, no figures an entire section adde
Error estimates for pi-pi scattering threshold parameters in Chiral Perturbation Theory to two loops
Using the analysis of ChPT to two loops, we perform an error analysis of the
threshold and low energy parameters, based on the uncertainties for the one
loop low energy parameters and the resonance saturation mechanism. Different
sets of one loop low energy constants have been considered.Thus, the predictive
power of the effective field theory is quantified on the basis of the present
experimental uncertainties.Comment: 12 pages, 2 tables, 3 figures. Numerics upgraded to v2 of ref.(8).
New reference added. Typos corrected. New figure for SU(3) parameters
include
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