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

Using the DFWM technique we determined rotational and vibrational temperatures of NaH molecules in a dynamical system consisting of NaH, Na, H and H2 for several heat-pipe oven temperatures. We applied a new way to determine the dependence of the DFWM signalIcint on the power of the transition dipole momentµ without previous knowledge of the temperature. The revealed dependence isIcintαµ4. In this case the laser intensities were found to be of the same order as the saturation intensity in accordance with simple DFWM theory. A usual Boltzmann plot was employed for the determination of the relevant rotational temperatures, which displayed higher values than the oven temperature.

Rotational and vibrational temperature determination by dfwm spectroscopy

We present an iterative analytic solution for the time dynamics of the $^{87}\text{R}\text{b}$ four-level atoms excited by a train of ultrashort pulses. It enables fast and accurate calculation of the system time evolution circumventing the use of time-consuming numerical procedures. The obtained solution is used to study the complex interaction of atoms with the pulse-train electric field, both in time and frequency domain. We investigate the influence of pulse-train physical parameters, such as the pulse peak power, the repetition frequency and the central laser wavelength on the accumulation of population and coherence in the system characterized by relaxation times larger than the pulse repetition period.

Time dynamics of a multilevel system excited by a train of ultrashort pulses

We present a simple model of ultracold cesium dimer formation in which the photoassociation into rovibrational levels of the double-minimum Cs{sub 2} 3 {sup 1}{sigma}{sub u}{sup +} state above its internal barrier enables spontaneous or stimulated emission into the lowest rovibrational levels of the Cs{sub 2} 1(X) {sup 1}{sigma}{sub g}{sup +} ground electronic state. The transition dipole moment should be sufficiently large for observation of such spectral transitions. The use of the Cs{sub 2} 3 {sup 1}{sigma}{sub u}{sup +} double-minimum potential could be extended to molecular Bose-Einstein condensates in which an optical trap can be employed for trapping of both atomic and molecular species.

Formation of ultracold Cs{sub 2} molecules through the double-minimum Cs{sub 2} 3 {sup 1}{sigma}{sub u}{sup +} state

We calculated the approximate form of absorption bands of RbCs molecules in the 450–1000 nm wavelength range. The manifold of potential curves for the Hund’s coupling case a was used to predict the absorption spectra assuming constant transition dipole moments, which can serve as a first approximation for the comparison with experimental results and their interpretation. Any substantial departure of an observed spectrum from the predicted one would point to the need of more complex calculations comprising transition-dipole-moment functions and spin–orbit interaction. Comparison with RbCs absorption bands from hot vapor is discussed. The band at 717 nm is identified as the 11Σ+→11Π transition (B–X band) and the diffuse band at 563 nm as the 11Σ+→31Π transition.

Goran Pichler

Papers

Rotational and vibrational temperature determination by dfwm spectroscopy

Time dynamics of a multilevel system excited by a train of ultrashort pulses

Formation of ultracold Cs{sub 2} molecules through the double-minimum Cs{sub 2} 3 {sup 1}{sigma}{sub u}{sup +} state

RbCs bands observation and interpretation

Photoassociation and bound-bound excitation into the 2 2pi state of lizn,licd, and nazn molecules