1,604 research outputs found
Haldane Quantum Hall Effect for Light in a Dynamically Modulated Array of Resonators
Topological insulators have attracted abundant attention for a variety of
reasons -- notably, the possibility for lossless energy transport through edge
states `protected' against disorder. Topological effects like the Quantum Hall
state can be induced through a gauge field, which is however hard to create in
practice, especially for charge-neutral particles. One way to induce an
effective gauge potential is through a dynamic, time-periodic modulation of the
lattice confining such particles. In this way, the Haldane Quantum Hall effect
was recently observed in a cold atom system. Here, we show how this same effect
can be induced for light confined to a lattice of identical optical resonators,
using an on-site modulation of the resonant frequencies. We further demonstrate
the existence of one-directional edge states immune to back-scattering losses,
and discuss the possibilities for a practical implementation, which would
enable slow-light devices of unprecedented quality
Reduced transition probabilities for the gamma decay of the 7.8 eV isomer in Th
The reduced magnetic dipole and electric quadrupole transition probabilities
for the radiative decay of the Th 7.8 eV isomer to the ground state are
predicted within a detailed nuclear-structure model approach. We show that the
presence and decay of this isomer can only be accounted for by the Coriolis
mixing emerging from a remarkably fine interplay between the coherent
quadrupole-octupole motion of the nuclear core and the single-nucleon motion
within a reflection-asymmetric deformed potential. We find that the magnetic
dipole transition probability which determines the radiative lifetime of the
isomer is considerably smaller than presently estimated. The so-far disregarded
electric quadrupole component may have non-negligible contributions to the
internal conversion channel. These findings support new directions in the
experimental search of the Th transition frequency for the development
of a future nuclear frequency standard.Comment: 5 pages, 1 figure, supplementary material is available as pdf with
the source files, v3 includes small corrections to match the published
version, results unchange
Long-distance radiative excitation transfer between quantum dots in disordered photonic crystal waveguides
We theoretically investigate the magnitude and range of the photon-mediated
interaction between two quantum dots embedded in a photonic crystal waveguide,
including fabrication disorder both in the crystal and in the dot positioning.
We find that disorder-induced light localization has a drastic effect on the
excitation transfer rate - as compared to an ideal structure - and that this
rate varies widely among different disorder configurations. Nevertheless, we
also find that significant rates of 50 micro-eV at a range of 10 micro-meters
can be achieved in realistic systems.Comment: 5 pages, 3 figure
Radiative coupling of quantum dots in photonic crystal structures
We derive a general formalism to model the polariton states resulting from
the radiation-matter interaction between an arbitrary number of excitonic
transitions in semiconductor quantum dots and photon modes in a photonic
crystal structure in which the quantum dots are embedded. The Maxwell
equations, including the linear nonlocal susceptibility of the exciton
transitions in the quantum dots, are cast into an eigenvalue problem, which can
be applied to any structure whose photon modes can be computed with reliable
accuracy, and in addition naturally allows for disorder effects to be taken
into account. We compute realistic photon modes using Bloch-mode expansion. As
example systems, we study typical InGaAs quantum dots in a GaAs photonic
crystal structures -- an cavity or a waveguide. For a single
dot, we reproduce known analytical results, while for the two dot case, we
study the radiative excitation transfer mechanism and characterize its
strength, the dependence on the detuning between quantum dot and photon modes,
and the dependence on inter-dot distance. We find in particular that the
inter-dot radiative coupling strength can reach in a short
cavity, and its decay with distance in longer cavities and waveguides is
determined by the group velocity of the exchanged photons and their radiative
lifetime. We also show that, for an cavity of increasing length, the
radiative excitation transfer mechanism is subject to a crossover from a regime
where a single photon mode is dominating, to a multi-mode regime -- occurring
around = 150 for the system under study.Comment: 17 pages, 12 figure
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