Femtosecond filamentation in transparent media

There is growing interest in states of matter with topological order. These are characterized by highly stable ground states robust to perturbations that preserve the topology, and which support excitations with so-called anyonic statistics. Topologically ordered states can arise in two-dimensional lattice-spin models, which were proposed as the basis for a new class of quantum computation. Here, we show that the relevant hamiltonians for such spin lattice models can be systematically engineered with polar molecules stored in optical lattices, where the spin is represented by a single-valence electron of a heteronuclear molecule. The combination of microwave excitation with dipole–dipole interactions and spin–rotation couplings enables building a complete toolbox for effective two-spin interactions with designable range, spatial anisotropy and coupling strengths significantly larger than relevant decoherence rates. Finally, we illustrate two models: one with an energy gap providing for error-resilient qubit encoding, and another leading to topologically protected quantum memory.

https://arxiv.org/pdf/quant-ph/0512222.pdf

A toolbox for lattice-spin models with polar molecules

The authors review progress in understanding the nature of atomic collisions occurring at temperatures ranging from the millidegrees Kelvin to the nanodegrees Kelvin regime. The review includes advances in experiments with atom beams, light traps, and purely magnetic traps. Semiclassical and fully quantal theories are described and their appropriate applicability assessed. The review divides the subject into two principal categories: collisions in the presence of one or more light fields and ground-state collisions in the dark.

Experiments and theory in cold and ultracold collisions

Photoassociation is the process in which two colliding atoms absorb a photon to form an excited molecule. The development of laser-cooling techniques for producing gases at ultracold !!1 mK" temperatures allows photoassociation spectroscopy to be performed with very high spectral resolution. Of particular interest is the investigation of molecular states whose properties can be related, with high precision, to the properties of their constituent atoms with the “complications” of chemical binding accounted for by a few parameters. These include bound long-range or purely long-range vibrational states in which two atoms spend most or all of their time at large internuclear separations. Low-energy atomic scattering states also share this characteristic. Photoassociation techniques have made important contributions to the study of all of these. This review describes what is special about photoassociation spectroscopy at ultracold temperatures, how it is performed, and a sampling of results including the determination of scattering lengths, their control via optical Feshbach resonances, precision determinations of atomic lifetimes from molecular spectra, limits on photoassociation rates in a Bose-Einstein condensate, and briefly, production of cold molecules. Discussions are illustrated with examples on alkali-metal atoms as well as other species. Progress in the field is already past the point where this review can be exhaustive, but an introduction is provided on the capabilities of photoassociation spectroscopy and the techniques presently in use.

/pdf/ultracold-photoassociation-spectroscopy-long-range-molecules-31d6x6vqxx.pdf

Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering

Summary: Carbazole-based oligomeric and polymeric materials have been studied for almost 25 years for their unique electrical, electrochemical and optical properties. Interestingly, carbazole units can be linked in two different ways leading to either poly(3,6-carbazole) or poly(2,7-carbazole) derivatives. While the former class seems to be very interesting for electrochemical and phosphorescence applications, the latter shows very promising optical properties in the visible range for light emitting diodes (LED). The major intrinsic difference between these two classes is the effective conjugation length: poly(2,7-carbazole) materials having the longer one, due to their poly(p-phenylene)-like structure. Using different synthetic strategies and substitution patterns, the physico-chemical properties of both classes can be fine-tuned, leading to high performance materials for a large number electronic applications.

Chemical structures for poly(3,6-carbazole) and poly(2,7-carbazole) and the materials used as the starting points for their respective syntheses.

Polycarbazoles: 25 Years of Progress

Dye-laser, tuned over the self-broadened wings of the sodiumD-lines, was used for the excitation of sodium dimer diffuse bands in the region from 400 nm to 455 nm. The fluorescence and selected excitation spectra for various spectral phenomena at different experimental conditions have been obtained and analyzed. The models for the qualitative explanation of the excitation mechanism are discussed.

A study of Na2 diffuse bands in violet by the excitation through self-broadenedD-lines

We investigated emission spectrum of LiH molecules from an electric discharge in a heat-pipe oven. The optimal conditions for the most intense LiH emission regarding the vapour pressures of helium, hydrogen and lithium were found to be 2.5 Torr, 8.5 Torr and 0.9 mTorr, respectively. The important role of helium gas in increasing the LiH emission intensity is described. The number density of the lithium atoms in the first excited state, Li(2p) and the LiH emission, was measured for different hydrogen pressures and currents through the discharge. We found that one part of the LiH molecules formed in the discharge is created in chemical quenching of excited lithium atoms by H2 . We performed the theoretical simulations for observed LiH A 1 + -X 1 + emission band. The rotational temperature and the population distribution of vibrational levels in the LiH A 1 + state were determined. We also describe the search for emission from the LiH C 1 + electronic state in the spectrum, which at present is unsuccessful.

http://iopscience.iop.org/article/10.1088/0022-3727/33/4/313/pdf

LiH emission spectrum from the glow discharge in a heat-pipe oven

/pdf/kolorimetrijska-prosudba-ucinkovitosti-razlicitih-postupaka-2usard2zbp.pdf

Kolorimetrijska prosudba učinkovitosti različitih postupaka izbjeljivanja zuba

We report absorption measurements in pure cesium vapor at high temperatures, when triplet absorption bands in the spectral interval 540–560 nm emerge within the singlet molecular bands which slowly diminish due to efficient thermal dissociation. The absorption bands have been identified as stemming from extrema in the Cs2 3 3Πg-a 3Σu+ difference potential curve. We performed a quasiclassical simulation which agrees well with experimental observation. Since the Cs2 a 3Σu+ state is only weakly bound, the observed absorption bands at 543.5 and 557 nm represent free-bound transitions or the photoassociation process.

/pdf/photoassociation-of-cesium-atoms-into-cs2-3-3pg-state-at-543-4zv4yoyj5z.pdf

Photoassociation of cesium atoms into Cs2 3 3Πg state at 543.5 nm

We present experimental and theoretical studies of the absorption spectrum of Na–K–He mixture. Semiclassical spectral simulations in the 400–850 nm wavelength range were performed, on the basis of available interaction potential curves for Na2, K2, NaK, NaHe and KHe molecules. Calculated absorption spectra were analysed and compared to the experimental absorption spectrum of Na–K–He mixture generated in a gravitational heat pipe oven.

https://iopscience.iop.org/article/10.1088/0953-4075/38/17/003/pdf

Goran Pichler

Papers

A study of Na2 diffuse bands in violet by the excitation through self-broadenedD-lines

LiH emission spectrum from the glow discharge in a heat-pipe oven

Kolorimetrijska prosudba učinkovitosti različitih postupaka izbjeljivanja zuba

Photoassociation of cesium atoms into Cs2 3 3Πg state at 543.5 nm

Absorption spectrum of Na-K-He mixture : experiment and theory