Cavity QED models are analyzed in terms of field quadrature operators. We demonstrate that in such representation, the problem can be formulated in terms of effective gauge potentials. In this respect, it presents a completely new system in which gauge fields arise, possessing the advantages of purity, high control of system parameters as well as preparation and detection methods. Studying three well known models, it is shown that either Abelian or non-Abelian gauge potentials can be constructed. The non-Abelian characteristics are evidenced via numerical simulations utilizing experimental parameters.

The eigenenergies and root mean square radii of the rovibrational levels (J = 0-3) of the weakly bound bosonic van der Waals neon trimer were calculated using a full angular momentum three-dimensional finite element method. The differing results of three previous studies for zero angular momentum are discussed, explained, and compared with the results presented here.

We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H++H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, lambda_{dB}, as small as 25 fm.

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We present experimental evidence for a strong dependence on the angle between the molecular axis of H 2 and the direction of the incoming projectile ͑p͒ in the cross section for transfer excitation in fast p-H 2 collisions. For collision energies of 1.0 and 1.3 MeV we find good agreement between the observed data and an analytical expression based on a two-atomic-center description using Brinkman-Kramers amplitudes. This clearly shows that the observed angular dependence is a result of quantum mechanical interference and not a trivial geometrical effect.Experimental indications and verifications of quantum mechanical interference effects continue to spur considerable interest and discussions, although such effects are wellknown consequences of the wave description of matter ͑which has been around for almost a century͒. One example of a recent discussion concerns the observation of interference effects in electron emission from randomly oriented H 2 molecules in fast charged-particle collision ͓1-7͔. In this Rapid Communication we report on collisions between fast protons and fixed-in-space H 2 where we observe strong interferences of electron-transfer amplitudes for the two centers leading to molecular-orientation dependences in the electron transfer cross section. In 1960 Tuan and Gerjuoy ͓8͔ formulated the problem of electron transfer in atom-molecule collisions in terms of a separated-atoms picture with interfering electron-transfer amplitudes. A similar description for scattering amplitudes was employed by Deb et al. ͓9͔ in 1988 considering the "two-slit" problem of high-velocity electron capture from an oriented hydrogen molecule for which the projectile has to pass close by one of the target nuclei ͓10͔. Shingal and Lin ͓11͔ used a semiclassical approach in combination with close-coupling electron transfer amplitudes to calculate strong variations in electron transfer cross sections as functions of the molecular orientations for 1 -500 keV. Later Wang, McGuire, and Rivarola ͓12͔ deduced an analytical expression, based on Brinkman-Kramers amplitudes ͓13͔, and valid for high energies ͑ജ1 MeV͒.Due to the very small electron-transfer cross sections at high energies ͓14͔, experiments are difficult and the only earlier investigation of the molecular orientation dependence was performed with O 8+ increasing the count rate by a large factor ͓15͔ in relation to the proton projectile case. However, using O 8+ instead of protons makes comparisons with model calculations that rely on small values of the projectile charge-to-velocity parameter Z p / v p , more difficult. Further-more capture to excited projectile states becomes important as the projectile charge is increased ͓16͔. In the present paper we have utilized the unique properties of the ion storage and cooler ring CRYRING with its internal gas-jet target to improve the luminosity by orders of magnitude compared to earlier studies ͑c.f. ͓17-20͔͒. This has allowed us to investigate two-center interference effects in electron-transfer for p H 2 with Z p = 1 and v...

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A three-dimensional finite element method is applied to the ground states of the symmetric and asymmetric atomic helium trimers 4 He 3 and 4 He 2 -3 He. Three different He-He interaction potentials of hard-core nature were studied. Two extrapolation procedures based on the convergence properties of the finite element method are investigated.