No abstract

The triplet s-wave scattering length of 6 Li is determined using two-photon photoassociative spectroscopy of the diatomic a 3 ⌺ u ϩ state of 6 Li 2 . The measured binding energy of the highest-lying bound state, combined with knowledge of the potential, determines the s-wave scattering length to be ͑Ϫ2160Ϯ250)a 0 , where a 0 is the Bohr radius. This extraordinarily large scattering length signifies a near-threshold resonance. A complete table of singlet and triplet scattering lengths for collisions involving 6 Li and 7 Li determined from this and our previous spectroscopic investigations is given.

We initiate the study of relaxation to quantum equilibrium over long timescales in pilot-wave theory. We simulate the time evolution of the coarse-grained H-functionH(t) for a two-dimensional harmonic oscillator. For a (periodic) wave function that is a superposition of the first 25 energy states we confirm an approximately exponential decay ofH over five periods. For a superposition of only the first four energy states we are able to calculateH(t) over 50 periods. We find that, depending on the set of phases in the initial wave function,H can decay to a large nonequilibrium residue exceeding 10% of its initial value or it can become indistinguishable from zero (the equilibrium value). We show that a large residue inH is caused by a tendency for the trajectories to be confined to sub-regions of configuration space for some wave functions, and that this is less likely to occur for larger numbers of energy states (if the initial phases are chosen randomly). Possible cosmological implications are briefly discussed.

We determine the radial dipole moment between the 2S and 2 P states of atomic lithium by analyzing the long-range vibrational eigenenergies of the singly excited diatomic molecule. The result can be expressed in terms of the 2 P 1/2 radiative lifetime of 7 Li, which is found to be 27.102(2)(7) ns. This result agrees with most current atomic-structure calculations and resolves the long-standing disagreement with previous experiment. The current level of precision is sensitive to relativistic effects in the atomic-structure calculation and to non-Born-Oppenheimer and radiation retardation effects in the molecule. ͓S1050-2947͑96͒50307-0͔ PACS number͑s͒: 32.70. Cs, 34.20.Cf, 31.30.Jv Atomic radiative lifetimes are known to be sensitive tests of atomic-structure calculations. The relatively simple structure of atomic lithium makes it a viable candidate for testing the various ab initio techniques which, in recent years, have grown in both sophistication and accuracy ͓1-8͔. A recent calculation of the 2S↔2 P nonrelativistic oscillator strength by Yan and Drake ͓8͔ has an estimated uncertainty of only 1.0ϫ10 Ϫ6 . Experimentally, the most precisely stated measurement of a radiative lifetime for a multielectron atom is the measurement of the 2 P lifetime of lithium by Gaupp et al. ͓9͔, with a one standard deviation uncertainty of 1.5ϫ10 Ϫ3 . Unfortunately, the experimental result and most calculations disagree by more than four standard deviations. Resolution of this large discrepancy is motivated by the need to apply atomic-structure calculations to more complicated atoms. In particular, atomic theory is crucial for interpreting parity violation in experiments with cesium ͓10͔. Clearly, there is a strong need for finding alternative methods of precisely measuring this value.Radiative dipole moments can be determined by analyzing the spectra of long-range, singly excited diatomic molecules. Photoassociative spectroscopy of ultracold atoms is a powerful tool for probing these high-lying molecular vibrational states ͓11͔. In previous work, we used this technique to observe the highest vibrational levels of the A 1 ⌺ u ϩ state of 6 Li 2 and 7 Li 2 ͓12͔. The long-range portion of this potential arises from a resonant dipole-dipole interaction that has the functional form V(R)ϭϪC 3 /R 3 . The coefficient C 3 is inversely proportional to the 2 P atomic radiative lifetime, , by ͓13͔where is the wavelength of the atomic transition.In a previous publication, we constructed a model potential for the 1 3 ⌺ g ϩ manifold from a variety of ab initio and experimental sources ͓14͔. Eigenvalues from this model were calculated as a function of C 3 and fitted to the corresponding data. The estimated uncertainty of 6ϫ10 Ϫ3 was due to systematic uncertainties associated with parts of the model known only through ab initio calculation. However, since then, Linton et al. ͓15͔ have used Fourier transform spectroscopy of the A 1 ⌺ u ϩ state to measure a range of vibrational levels for which the highest-lying ones overlap the lower part of the...

Optical bistability is a general title for a number of static and dynamic phenomena that result from the interplay of optical non-linearity and feedback. The object of this review is to give a broad description of optical bistability: from practical applications, as an optical transistor or optical memory element, to its phase transition interpretation. The theory is divided into three parts. The first is a simple discussion that covers most of the basic experimental effects and concepts of practical importance. The second part applies to atomic systems where a semiclassical as well as a quantummechanical approach is possible. The third one discusses the mechanisms compatible with large non-linearities observed in InSb and GaAs as semiconductors constitute the most promising materials for applications. Current experimental progress in all-optical and hybrid devices is also discussed and finally a scaling example is presented to indicate the possibilities in high-speed all-optical signal processing.