2,963 research outputs found

### Radiation 'damping' in atomic photonic crystals

The force exerted on a material by an incident beam of light is dependent
upon the material's velocity in the laboratory frame of reference. This
velocity dependence is known to be diffcult to measure, as it is proportional
to the incident optical power multiplied by the ratio of the material velocity
to the speed of light. Here we show that this typically tiny effect is greatly
amplified in multilayer systems composed of resonantly absorbing atoms (e.g.
optically trapped 87Rb), which may exhibit ultra-narrow photonic band gaps. The
amplification of the effect is shown to be three orders of magnitude greater
than previous estimates for conventional photonic-band-gap materials, and
significant for material velocities of a few ms/s.Comment: 5 pages, 3 figure

### Exciton-phonon scattering and photo-excitation dynamics in J-aggregate microcavities

We have developed a model accounting for the photo-excitation dynamics and
the photoluminescence of strongly coupled J-aggregate microcavities. Our model
is based on a description of the J-aggregate film as a disordered Frenkel
exciton system in which relaxation occurs due to the presence of a thermal bath
of molecular vibrations. In a strongly coupled microcavity exciton-polaritons
are formed, mixing superradiant excitons and cavity photons. The calculation of
the microcavity steady-state photoluminescence, following a CW non resonant
pumping, is carried out. The experimental photoluminescence intensity ratio
between upper and lower polariton branches is accurately reproduced. In
particular both thermal activation of the photoluminescence intensity ratio and
its Rabi splitting dependence are a consequence of the bottleneck in the
relaxation, occurring at the bottom of the excitonic reservoir. The effects due
to radiative channels of decay of excitons and to the presence of a
paritticular set of discrete optical molecular vibrations active in relaxation
processes are investigared.Comment: 8 pages, 6 figure

### Interacting social processes on interconnected networks

We propose and study a model for the interplay between two different
dynamical processes --one for opinion formation and the other for decision
making-- on two interconnected networks $A$ and $B$. The opinion dynamics on
network $A$ corresponds to that of the M-model, where the state of each agent
can take one of four possible values ($S=-2,-1,1,2$), describing its level of
agreement on a given issue. The likelihood to become an extremist ($S=\pm 2$)
or a moderate ($S=\pm 1$) is controlled by a reinforcement parameter $r \ge 0$.
The decision making dynamics on network $B$ is akin to that of the
Abrams-Strogatz model, where agents can be either in favor ($S=+1$) or against
($S=-1$) the issue. The probability that an agent changes its state is
proportional to the fraction of neighbors that hold the opposite state raised
to a power $\beta$. Starting from a polarized case scenario in which all agents
of network $A$ hold positive orientations while all agents of network $B$ have
a negative orientation, we explore the conditions under which one of the
dynamics prevails over the other, imposing its initial orientation. We find
that, for a given value of $\beta$, the two-network system reaches a consensus
in the positive state (initial state of network $A$) when the reinforcement
overcomes a crossover value $r^*(\beta)$, while a negative consensus happens
for $r<r^*(\beta)$. In the $r-\beta$ phase space, the system displays a
transition at a critical threshold $\beta_c$, from a coexistence of both
orientations for $\beta<\beta_c$ to a dominance of one orientation for
$\beta>\beta_c$. We develop an analytical mean-field approach that gives an
insight into these regimes and shows that both dynamics are equivalent along
the crossover line $(r^*,\beta^*)$.Comment: 25 pages, 6 figure

### Coherent perfect absorption in one-sided reflectionless media

In optical experiments one-sided reflectionless (ORL) and coherent perfect absorption (CPA) are unusual scattering properties yet fascinating for their fundamental aspects and for their practical interest. Although these two concepts have so far remained separated from each other, we prove that the two phenomena are indeed strictly connected. We show that a CPA-ORL connection exists between pairs of points lying along lines close to each other in the 3D space-parameters of a realistic lossy atomic photonic crystal. The connection is expected to be a generic feature of wave scattering in non-Hermitian optical media encompassing, as a particular case, wave scattering in parity-time (PT) symmetric media

### Non-Hermitian Degeneracies and Unidirectional Reflectionless Atomic Lattices

Light propagation in optical lattices of driven cold atoms exhibits non-Hermitian degeneracies when the first-order modulation amplitudes of real and imaginary parts of the probe susceptibility are manipulated to be balanced. At these degeneracies, one may observe complete unidirectional reflectionless light propagation. This strictly occurs with no gain and can be easily tuned and fully reversed as supported by the transfer-matrix calculations and explained via a coupled-mode analysis

### Polarization-selective optical nonlinearities in cold Rydberg atoms

We study the interaction between a probe and a trigger weak fields in a sample of cold rubidium atoms in the presence of a coupling and a dressing strong fields. Dipole Rydberg blockade may occur and can be set to depend on the probe and trigger polarizations giving rise to diverse regimes of electromagnetically induced transparency (EIT) with a concomitant small probe and trigger absorption and dispersion. This is shown to be relevant to the implementation of polarization conditional probe and trigger cross nonlinearities in cold Rydberg atoms

### Perfect absorption and no reflection in disordered photonic crystals

Understanding the effects of disorder on the light propagation in
photonic devices is of major importance from both fundamental and
applied points of view. Unidirectional reflectionless and coherent
perfect absorption of optical signals are unusual yet fascinating
phenomena that have recently sparked an extensive research effort in
photonics. These two phenomena, which arise from topological
deformations of the scattering matrix S parameters space, behave
differently in the presence of different types of disorder, as we show
here for a lossy photonic crystal prototype with a parity-time
antisymmetric susceptibility or a more general non-Hermitian one

### Role of anisotropy in the F\"orster energy transfer from a semiconductor quantum well to an organic crystalline overlayer

We consider the non-radiative resonant energy transfer from a two-dimensional
Wannier exciton (donor) to a Frenkel exciton of a molecular crystal overlayer
(acceptor). We characterize the effect of the optical anisotropy of the organic
subsystem on this process. Using realistic values of material parameters, we
show that it is possible to change the transfer rate within typically a factor
of two depending on the orientation of the crystalline overlayer. The resonant
matching of donor and acceptor energies is also partly tunable via the organic
crystal orientation.Comment: 6 pages, 8 figure

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