505 research outputs found
Quantum theory of photonic crystal polaritons
We formulate a full quantum mechanical theory of the interaction between
electromagnetic modes in photonic crystal slabs and quantum well excitons
embedded in the photonic structure. We apply the formalism to a high index
dielectric layer with a periodic patterning suspended in air. The strong
coupling between electromagnetic modes lying above the cladding light line and
exciton center of mass eigenfunctions manifests itself with the typical
anticrossing behavior. The resulting band dispersion corresponds to the
quasi-particles coming from the mixing of electromagnetic and material
excitations, which we call photonic crystal polaritons. We compare the results
obtained by using the quantum theory to variable angle reflectance spectra
coming from a scattering matrix approach, and we find very good quantitative
agreement.Comment: Proceedings of the "8th Conference on Optics of Excitons in Confined
Systems" (OECS-8), 15-17 September 2003, Lecce (Italy
A proposed study of multiple scattering through clouds up to 1 THz
A rigorous computation of the electromagnetic field scattered from an atmospheric liquid water cloud is proposed. The recent development of a fast recursive algorithm (Chew algorithm) for computing the fields scattered from numerous scatterers now makes a rigorous computation feasible. A method is presented for adapting this algorithm to a general case where there are an extremely large number of scatterers. It is also proposed to extend a new binary PAM channel coding technique (El-Khamy coding) to multiple levels with non-square pulse shapes. The Chew algorithm can be used to compute the transfer function of a cloud channel. Then the transfer function can be used to design an optimum El-Khamy code. In principle, these concepts can be applied directly to the realistic case of a time-varying cloud (adaptive channel coding and adaptive equalization). A brief review is included of some preliminary work on cloud dispersive effects on digital communication signals and on cloud liquid water spectra and correlations
Energy- and temperature-dependent transport of integral proteins to the inner nuclear membrane via the nuclear pore
Resident integral proteins of the inner nuclear membrane (INM) are synthesized as membrane-integrated proteins on the peripheral endoplasmic reticulum (ER) and are transported to the INM throughout interphase using an unknown trafficking mechanism. To study this transport, we developed a live cell assay that measures the movement of transmembrane reporters from the ER to the INM by rapamycin-mediated trapping at the nuclear lamina. Reporter constructs with small (<30 kD) cytosolic and lumenal domains rapidly accumulated at the INM. However, increasing the size of either domain by 47 kD strongly inhibited movement. Reduced temperature and ATP depletion also inhibited movement, which is characteristic of membrane fusion mechanisms, but pharmacological inhibition of vesicular trafficking had no effect. Because reporter accumulation at the INM was inhibited by antibodies to the nuclear pore membrane protein gp210, our results support a model wherein transport of integral proteins to the INM involves lateral diffusion in the lipid bilayer around the nuclear pore membrane, coupled with active restructuring of the nuclear pore complex
Organellar proteomics: the prizes and pitfalls of opening the nuclear envelope
Proteomic studies have the potential to comprehensively define the composition of organelles but are limited by the organellar cross-contamination that arises during subcellular fractionation. Comparative proteomics of organellar subfractions can mitigate these problems, as demonstrated by a recent study involving the nuclear envelope
Optimizing band-edge slow light in silicon-on-insulator waveguide gratings
A systematic analysis of photonic bands and group index in silicon grating waveguides is performed, in order to optimize band-edge slow-light behavior in integrated structures with low losses. A combination of numerical methods and perturbation theory is adopted. It is shown that a substantial increase of slow light bandwidth is achieved when decreasing the internal width of the waveguide and the silicon thickness in the cladding region. It is also observed that a reduction of the internal width does not undermine the performance of an adiabatic taper
YBCO microwave resonators for strong collective coupling with spin ensembles
Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have
been realized and characterized in a wide temperature (, 2-100 K) and
magnetic field (, 0-7 T) range. The quality factor exceeds 10
below 55 K and it slightly decreases for increasing fields, remaining 90 of
for T and K. These features allow the coherent coupling
of resonant photons with a spin ensemble at finite temperature and magnetic
field. To demonstrate this, collective strong coupling was achieved by using
DPPH organic radical placed at the magnetic antinode of the fundamental mode:
the in-plane magnetic field is used to tune the spin frequency gap splitting
across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings
are observed with a splitting as large as MHz at K. The
spin-cavity collective coupling rate is shown to scale as the square root of
the number of active spins in the ensemble.Comment: to appear in Appl. Phys. Let
Optimal condition to probe strong coupling of two-dimensional excitons and zero-dimensional cavity modes
The light-matter interaction associated with a two-dimensional excitonic transition coupled to a zero-dimensional photonic cavity is fundamentally different from cavity-coupled localized excitations in quantum dots or color centers, which have negligible spatial extent compared to the cavity-confined mode profile. We provide a succinct expression for calculating the light-matter interaction of a two-dimensional optical transition coupled to a zero-dimensional confined cavity mode. From this expression, we found there is an optimal spatial extent of the excitonic transition that maximizes such an interaction strength due to the competition between minimizing the excitonic envelope function area and maximizing the total integrated field. We also found that at near zero exciton-cavity detuning, the direct transmission efficiency of a waveguide-integrated cavity can be severely suppressed, which suggests performing experiments using a side-coupled cavity
Exciton polaritons in two-dimensional photonic crystals
Experimental evidence of strong coupling between excitons confined in a
quantum well and the photonic modes of a two-dimensional dielectric lattice is
reported. Both resonant scattering and photoluminescence spectra at low
temperature show the anticrossing of the polariton branches, fingerprint of
strong coupling regime. The experiments are successfully interpreted in terms
of a quantum theory of exciton-photon coupling in the investigated structure.
These results show that the polariton dispersion can be tailored by properly
varying the photonic crystal lattice parameter, which opens the possibility to
obtain the generation of entangled photon pairs through polariton stimulated
scattering.Comment: 5 pages, 4 figure
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