53 research outputs found
Collective states in highly symmetric atomic configurations, and single-photon traps
Abbreviated Abstract: We study correlated states in a circular and
linear-chain configuration of identical two-level atoms containing the energy
of a single quasi-resonant photon in the form of a collective excitation, where
the collective behaviour is mediated by exchange of transverse photons between
the atoms. For a circular configuration of atoms the effective Hamiltonian on
the radiationless subspace of the system can be diagonalized analytically. In
this case, the radiationless energy eigenstates carry a quantum
number which is analogous to the angular momentum quantum
number , carried by particles propagating in a central potential,
such as a hydrogen-like system. Just as the hydrogen s-states are the only
electronic wave functions which can occupy the central region of the Coulomb
potential, the quasi-particle corresponding to a collective excitation of the
circular atomic sample can occupy the central atom only for vanishing
quantum number . For large numbers of atoms in a maximally
subradiant state, a critical interatomic distance of emerges both
in the linear-chain and the circular configuration of atoms. The spontaneous
decay rate of the linear configuration exhibits a jump-like "critical"
behaviour for next-neighbour distances close to a half-wavelength. Furthermore,
both the linear-chain and the circular configuration exhibit exponential photon
trapping once the next-neighbour distance becomes less than a half-wavelength,
with the suppression of spontaneous decay being particularly pronounced in the
circular system. In this way, circular configurations containing sufficiently
many atoms may be natural candidates for {\it single-photon traps}.Comment: Invited contribution to "Xth International Conference on Quantum
Optics ICQO 2004" in Minsk, Belarus. To be published in Optics and
Spectroscop
Digalactosyl-diacylglycerol-deficiency lowers the thermal stability of thylakoid membranes
We investigated the effects of digalactosyl-diacylglycerol (DGDG) on the organization and thermal stability of thylakoid membranes, using wild-type Arabidopsis thaliana and the DGDG-deficient mutant, dgd1. Circular-dichroism measurements reveal that DGDG-deficiency hampers the formation of the chirally organized macrodomains containing the main chlorophyll a/b light-harvesting complexes. The mutation also brings about changes in the overall chlorophyll fluorescence lifetimes, measured in whole leaves as well as in isolated thylakoids. As shown by time-resolved measurements, using the lipophylic fluorescence probe Merocyanine 540 (MC540), the altered lipid composition affects the packing of lipids in the thylakoid membranes but, as revealed by flash-induced electrochromic absorbance changes, the membranes retain their ability for energization. Thermal stability measurements revealed more significant differences. The disassembly of the chiral macrodomains around 55°C, the thermal destabilization of photosystem I complex at 61°C as detected by green gel electrophoresis, as well as the sharp drop in the overall chlorophyll fluorescence lifetime above 45°C (values for the wild type—WT) occur at 4–7°C lower temperatures in dgd1. Similar differences are revealed in the temperature dependence of the lipid packing and the membrane permeability: at elevated temperatures MC540 appears to be extruded from the dgd1 membrane bilayer around 35°C, whereas in WT, it remains lipid-bound up to 45°C and dgd1 and WT membranes become leaky around 35 and 45°C, respectively. It is concluded that DGDG plays important roles in the overall organization of thylakoid membranes especially at elevated temperatures
Precision experiments on muonium 3 Ramsey resonance in zero field
Journals published by the American Physical Society can be found at http://publish.aps.org
Amplitude squeezing in a Mach-Zehnder fiber interferometer: Numerical analysis of experiments with microstructure fiber”, Opt
Abstract: We study a Mach-Zehnder nonlinear fiber interferometer for the generation of amplitude-squeezed light. Numerical simulations of experiments with microstructure fiber are performed using linearization of the quantum nonlinear Shrödinger equation. We include in our model the effect of distributed linear losses in the fiber
Successful transvaginal ultrasound-guided ablation of a cervical pregnancy in a patient with simultaneous intrauterine pregnancy after in vitro
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