2,826 research outputs found
Radiative Corrections to Multi-Level Mollow-Type Spectra
This paper is concerned with two rather basic phenomena: the incoherent
fluorescence spectrum of an atom driven by an intense laser field and the
coupling of the atom to the (empty) modes of the radiation field. The sum of
the many-photon processes gives rise to the inelastic part of the atomic
fluorescence, which, for a two-level system, has a well-known characteristic
three-peak structure known as the Mollow spectrum. From a theoretical point of
view, the Mollow spectrum finds a natural interpretation in terms of
transitions among laser-dressed states which are the energy eigenstates of a
second-quantized two-level system strongly coupled to a driving laser field. As
recently shown, the quasi-energies of the laser-dressed states receive
radiative corrections which are nontrivially different from the results which
one would expect from an investigation of the coupling of the bare states to
the vacuum modes. In this article, we briefly review the basic elements
required for the analysis of the dynamic radiative corrections, and we
generalize the treatment of the radiative corrections to the incoherent part of
the steady-state fluorescence to a three-level system consisting of 1S, 3P and
2S states.Comment: Dedicated to Prof. H. Walther on the occasion of his 70th birthda
An optical diode made from a `flying' photonic crystal
Optical diodes controlling the flow of light are of principal significance
for optical information processing 1. They transmit light from an input to an
output, but not in reverse direction. This breaking of time reversal symmetry
is typically achieved via non-linear 2,3 or magnetic effects 4, which imposes
limits to all-optical control 5-7, on-chip integration 7-11, or single-photon
operation 12. Here, we propose an optical diode which requires neither magnetic
fields nor strong input fields. It is based on a flying photonic crystal. Due
to the Doppler effect, the crystal has a band gap with frequency depending on
the light propagation direction relative to the crystal motion.
Counter-intuitively, our setup does not involve the movement of any material
parts. Rather, the flying photonic crystal is realized by optically inducing a
spatially periodic but moving modulation of the optical properties of a
near-resonant medium. The flying crystal not only opens perspectives for
optical diodes operating at low light levels or integrated in small solid state
devices, but also enables novel photonic devices such as optically tunable
mirrors and cavities.Comment: 13 pages, 4 figures, presented in PQE 201
Analysis of the effects of baffles on combustion instability
An analytical model has been developed for predicting the effects of baffles on combustion instability. This model has been developed by coupling an acoustic analysis of the wave motion within baffled chambers with a model for the oscillatory combustion response of a propellant droplet developed by Heidmann. A computer program was developed for numerical solution of the resultant coupled equations. Diagnostic calculations were made to determine the reasons for the improper prediction. These calculations showed that the chosen method of representing the combustion response was a very poor approximation. At the end of the program, attempts were made to minimize this effect but the model still improperly predicts the stability trends. Therefore, it is recommended that additional analysis be done with an improved approximation
Strong-field spatial interference in a tailored electromagnetic bath
Light scattered by a regular structure of atoms can exhibit interference
signatures, similar to the classical double-slit. These first-order
interferences, however, vanish for strong light intensities, restricting
potential applications. Here, we show how to overcome these limitations to
quantum interference in strong fields. First, we recover the first-order
interference in strong fields via a tailored electromagnetic bath with a
suitable frequency dependence. At strong driving, the optical properties for
different spectral bands are distinct, thus extending the set of observables.
We further show that for a two-photon detector as, e.g., in lithography,
increasing the field intensity leads to twice the spatial resolution of the
second-order interference pattern compared to the weak-field case.Comment: final versio
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Effects of Nuclear Structure on Quasi-fission
The quasi-fission mechanism hinders fusion of heavy systems because of a mass
flow between the reactants, leading to a re-separation of more symmetric
fragments in the exit channel. A good understanding of the competition between
fusion and quasi-fission mechanisms is expected to be of great help to optimize
the formation and study of heavy and superheavy nuclei. Quantum microscopic
models, such as the time-dependent Hartree-Fock approach, allow for a treatment
of all degrees of freedom associated to the dynamics of each nucleon. This
provides a description of the complex reaction mechanisms, such as
quasi-fission, with no parameter adjusted on reaction mechanisms. In
particular, the role of the deformation and orientation of a heavy target, as
well as the entrance channel magicity and isospin are investigated with
theoretical and experimental approaches.Comment: Invited talk to NSRT12. To be published in Eur. Phys. J. Web of Con
Novel insights into transfer processes in the reaction 16O+208Pb at sub-barrier energies
The collision of the doubly-magic nuclei O+Pb is a benchmark
in nuclear reaction studies. Our new measurements of back-scattered
projectile-like fragments at sub-barrier energies show show that transfer of 2
protons () is much more probable than -particle transfer.
transfer probabilities are strongly enhanced compared to expectations for the
sequential transfer of two uncorrelated protons; at energies around the fusion
barrier absolute probabilities for two proton transfer are similar to those for
one proton transfer. This strong enhancement indicates strong pairing
correlations in O, and suggests evidence for the occurrence of a nuclear
supercurrent of two-proton Cooper pairs in this reaction, already at energies
well below the fusion barrier.Comment: 5 pages, 3 figure
Multifractality at the spin quantum Hall transition
Statistical properties of critical wave functions at the spin quantum Hall
transition are studied both numerically and analytically (via mapping onto the
classical percolation). It is shown that the index characterizing the
decay of wave function correlations is equal to 1/4, at variance with the
decay of the diffusion propagator. The multifractality spectra of
eigenfunctions and of two-point conductances are found to be
close-to-parabolic, and .Comment: 4 pages, 3 figure
A Problematic Set of Two-Loop Self-Energy Corrections
We investigate a specific set of two-loop self-energy corrections involving
squared decay rates and point out that their interpretation is highly
problematic. The corrections cannot be interpreted as radiative energy shifts
in the usual sense. Some of the problematic corrections find a natural
interpretation as radiative nonresonant corrections to the natural line shape.
They cannot uniquely be associated with one and only one atomic level. While
the problematic corrections are rather tiny when expressed in units of
frequency (a few Hertz for hydrogenic P levels) and do not affect the
reliability of quantum electrodynamics at the current level of experimental
accuracy, they may be of importance for future experiments. The problems are
connected with the limitations of the so-called asymptotic-state approximation
which means that atomic in- and out-states in the S-matrix are assumed to have
an infinite lifetime.Comment: 12 pages, 3 figures (New J. Phys., in press, submitted 28th May
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