1,555 research outputs found
Spontaneous Decay in the Presence of Absorbing Media
After giving a summary of the basic-theoretical concept of quantization of
the electromagnetic field in the presence of dispersing and absorbing
(macroscopic) bodies, their effect on spontaneous decay of an excited atom is
studied. Various configurations such as bulk material, planar half space media,
spherical cavities, and microspheres are considered. In particular, the
influence of material absorption on the local-field correction, the decay rate,
the line shift, and the emission pattern are examined. Further, the interplay
between radiative losses and losses due to material absorption is analyzed.
Finally, the possibility of generating entangled states of two atoms coupled by
a microsphere-assisted field is discussed.Comment: 32 pages, 15 eps figures, contribution to Recent Research
Developments in Optics, to be published by Research Signpos
Physical Properties of the Narrow-Line Region of Low-Mass Active Galaxies
We present spectroscopic observations of 27 active galactic nuclei (AGN) with
some of the lowest black hole (BH) masses known. We use the high spectral
resolution and small aperture of our Keck data, taken with the Echellette
Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these
low-mass BHs. We investigate their emission-line properties and compare them
with those of AGN with higher-mass black holes. While we are unable to
determine absolute metallicities, some of our objects plausibly represent
examples of the low-metallicity AGN described by Groves et al. (2006), based on
their [N II]/H_alpha ratios and their consistency with the Kewley & Ellison
(2008) mass-metallicity relation. We find tentative evidence for steeper far-UV
spectral slopes in lower-mass systems. Overall, NLR emission lines in these
low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs,
such as increasing blueshifts and broadening with increasing ionization
potential. Additionally, we see evidence of an intermediate line region whose
intensity correlates with L/L_Edd, as seen in higher-mass AGN. We highlight the
interesting trend that, at least in these low-mass AGN, the [O III] equivalent
width (EW) is highest in symmetric NLR lines with no blue wing. This trend of
increasing [O III] EW with line symmetry could be explained by a high covering
factor of lower ionization gas in the NLR. In general, low-mass AGN preserve
many well-known trends in the structure of the NLR, while exhibiting steeper
ionizing continuum slopes and somewhat lower gas-phase metallicities.Comment: 46 pages, 14 figures, 7 table
Generation of long-living entanglement between two separate atoms
A scheme for non-conditional generation of long-living maximally entangled
states between two spatially well separated atoms is proposed. In the scheme,
-type atoms pass a resonator-like equipment of dispersing and
absorbing macroscopic bodies giving rise to body-assisted electromagnetic field
resonances of well-defined heights and widths. Strong atom-field coupling is
combined with weak atom-field coupling to realize entanglement transfer from
the dipole-allowed transitions to the dipole-forbidden transitions, thereby the
entanglement being preserved when the atoms depart from the bodies and from
each other. The theory is applied to the case of the atoms passing by a
microsphere.Comment: 13 pages, 5 figure
Efficiency of tunable band-gap structures for single-photon emission
The efficiency of recently proposed single-photon emitting sources based on
tunable planar band-gap structures is examined. The analysis is based on the
study of the total and ``radiative'' decay rates, the expectation value of
emitted radiation energy and its collimating cone. It is shown that the scheme
operating in the frequency range near the defect resonance of a defect band-gap
structure is more efficient than the one operating near the band edge of a
perfect band-gap structure.Comment: 9 pages, 7 figure
Chiral zero modes in non local domain walls
We study a generalization of the Callan-Harvey mechanism to the case of a non
local mass. Using a 2+1 model as a concrete example, we show that both the
existence and properties of localized zero modes can also be consistently
studied when the mass is non local. After dealing with some general properties
of the resulting integral equations, we show how non local masses naturally
arise when radiative corrections are included. We do that for a 2+1 dimensional
example, and also evaluate the zero mode of the resulting non local Dirac
operator.Comment: 20 pages, LaTeX, 4 figures; typos and content of sections 2 and 3
correcte
gl(N|N) Super-Current Algebras for Disordered Dirac Fermions in Two Dimensions
We consider the non-hermitian 2D Dirac Hamiltonian with (A): real random
mass, imaginary scalar potential and imaginary gauge field potentials, and (B)
arbitrary complex random potentials of all three kinds. In both cases this
Hamiltonian gives rise to a delocalization transition at zero energy with
particle-hole symmetry in every realization of disorder. Case (A) is in
addition time-reversal invariant, and can also be interpreted as the
random-field XY Statistical Mechanics model in two dimensions. The
supersymmetric approach to disorder averaging results in current-current
perturbations of super-current algebras. Special properties of the
algebra allow the exact computation of the beta-functions, and of the
correlation functions of all currents. One of them is the Edwards-Anderson
order parameter. The theory is `nearly conformal' and possesses a
scale-invariant subsector which is not a current algebra. For N=1, in addition,
we obtain an exact solution of all correlation functions. We also study the
delocalization transition of case (B), with broken time reversal symmetry, in
the Gade-Wegner (Random-Flux) universality class, using a GL(N|N;C)/U(N|N)
sigma model, as well as its PSL(N|N) variant, and a corresponding generalized
random XY model. For N=1 the sigma model is shown to be identical to the
current-current perturbation. For the delocalization transitions (case (A) and
(B)) a density of states, diverging at zero energy, is found.Comment: LaTeX, 40 page
Critical behavior of two-dimensional random hopping fermions with \pi-flux
A two dimensional random hopping model with N-species and \pi-flux is
studied. The field theory at the band center is shown to be in the universality
class of GL(4m,R)/O(4m) nonlinear sigma model. Vanishing beta function suggests
delocalised states at the band center. Contrary to the similar universality
class with broken time reversal symmetry, the present class is expected to have
at least two fixed point. Large N-systems are shown to be in the weak-coupling
fixed point, which is characterized by divergent density of state, while small
N systems may be in the strong-coupling fixed point.Comment: 12 pages, revtex, 1 figur
Input-output relations at dispersing and absorbing planar multilayers for the quantized electromagnetic field containing evanescent components
By using the Green-function concept of quantization of the electromagnetic
field in dispersing and absorbing media, the quantized field in the presence of
a dispersing and absorbing dielectric multilayer plate is studied.
Three-dimensional input-output relations are derived for both amplitude
operators in the -space and the field operators in the coordinate
space. The conditions are discussed, under which the input-output relations can
be expressed in terms of bosonic operators. The theory applies to both
(effectively) free fields and fields, created by active atomic sources inside
and/or outside the plate, including also evanescent-field components.Comment: 14 pages, 1 figur
Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, equations of motion and an effective Hamiltonian for treating both the
resonant dipole-dipole interaction between two-level atoms and the resonant
atom-field interaction are derived, which can suitably be used for studying the
influence of arbitrary dispersing and absorbing material surroundings on these
interactions. The theory is applied to the study of the transient behavior of
two atoms that initially share a single excitation, with special emphasis on
the role of the two competing processes of virtual and real photon exchange in
the energy transfer between the atoms. In particular, it is shown that for weak
atom-field interaction there is a time window, where the energy transfer
follows a rate regime of the type obtained by ordinary second-order
perturbation theory. Finally, the resonant dipole-dipole interaction is shown
to give rise to a doublet spectrum of the emitted light for weak atom-field
interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE
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