Research on matter waves is a thriving field of quantum physics and has recently stimulated many investigations with electrons 1 , neutrons 2 , atoms 3 , Bose-condensed ensembles 4 , cold clusters 5 and hot molecules 6 . Coherence experiments with complex objects are of interest for exploring the transition to classical physics 7-9 , for measuring molecular properties 10 , and they have even been proposed for testing new models of space-time 11 . For matter-wave experiments with complex molecules, the strongly dispersive effect of the interaction between the diffracted molecule and the grating wall is a major challenge because it imposes enormous constraints on the velocity selection of the molecular beam 12 . Here, we describe the first experimental realization of a new set-up that solves this problem by combining the advantages of a so-called Talbot-Lau interferometer 13 with the benefits of an optical phase grating.Several methods have been developed in the past for the coherent manipulation of matter waves with de Broglie wavelengths in the nanometre and picometre range. For instance, free-standing material gratings were used in the diffraction of electrons 14 , atoms 15,16 and molecules 5,6,17 . In addition, coherent beam splitting at non-resonant standing light waves, often designated the KapitzaDirac effect, has been observed for all of these species [18][19][20] . Recent implementations of near-field interferometry 13,[21][22][23] underlined the particular advantages of the Talbot-Lau concept for experiments with massive objects: the required grating period scales only weakly (d ∼ √ l) with the de Broglie wavelength, and the design accepts beams of low spatial coherence, which makes high signals possible even for weak sources.A symmetric Talbot-Lau interferometer (TLI) consists of three identical gratings. The first one prepares the transverse coherence of the weakly collimated beam. Quantum near-field diffraction at the second nanostructure generates a periodic molecular density distribution at the position of the third mask, which represents a self-image of the second grating, if the grating separation equals a multiple of the Talbot length L T = d 2 /l. The mask can be laterally shifted to transform the molecular interference pattern into a modulation of the molecular beam intensity that is recorded behind the interferometer.In the established TLI design with three nanofabricated gratings 23 , the molecule-wall interaction with the grating bars imprints a further phase shift ϕ on the matter wave, which depends on the molecular polarizability α, the velocity v z and the distance r to the wall within the grating slit. Because of its strongly nonlinear r-dependence, this interaction restricts the interference contrast to very narrow bands of de Broglie wavelengths, as we show in Fig. 1a for the example of the fullerene C 70 . In this simulation, we use the full Casimir-Polder potential 24 , even though the long-distance (retarded) approximation, decaying as α/r 4 , closely reproduces the results. The sha...

Photodetachment microscopy of the negative ions Si- and F- has made it possible to measure the electron affinities of silicon and fluorine with improved accuracy. The new recommended electron affinities of 28Si and 19F are 11 207.252(18) and 27 432.446(19) cm-1, i.e. 1.389 5220(24) and 3.401 1895(25) eV, respectively.

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A photodetachment experiment is performed on the v=0-->v=0 OH(-) detachment threshold. The weak O and S branches provide a signal strong enough to make amplitude measurements on all five O, P, Q, R, and S branches possible, which are used to fix the formulas for their relative intensities. Photodetachment microscopy is applied to 15 different thresholds of the P, Q, and R branches. The quantitative analysis of the interference patterns obtained does not show any effect of the dipole moment of OH, but yields a new measurement of the rotational parameters of OH(-)(v=0) and of the electron affinity of the molecule. The new recommended value for the electron affinity of (16)O(1)H is 14 740.982(7) cm(-1) or 1.827 648 7(11) eV.

A three-level Λ system in Tm 3+ doped YAG crystal is experimentally investigated in the prospect of quantum information processing. Zeeman effect is used to lift the nuclear spin degeneracy of this ion. In a previous paper [de Seze et al. Phys. Rev. B, 73, 85112 (2006)] we measured the gyromagnetic tensor components and concluded that adequate magnetic field orientation could optimize the optical connection of both ground state sublevels to each one of the excited state sublevels, thus generating Λ systems. Here we report on the direct measurement of the transition probability ratio along the two legs of the Lambda. Measurement techniques combine frequency selective optical pumping with optical nutation or photon echo processes.

We measure the coupling constant between the two perpendicularly polarized eigenstates of a two-frequency Vertical External Cavity Surface Emitting Laser (VECSEL). This measurement is performed for different values of the transverse spatial separation between the two perpendicularly polarized modes. The consequences of these measurements on the two-frequency operation of such class-A semiconductor lasers are discussed.

Electromagnetically induced transparency (EIT) is observed in gaseous 4 He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. Measurement of slow light opens up possible ways to applications.

We report the experimental observation of Coherent Population Oscillation (CPO) based light storage in an atomic vapor cell at room temperature. Using the ultranarrow CPO between the ground levels of a Λ system selected by polarization in metastable 4 He, such a light storage is experimentally shown to be phase preserving. As it does not involve any atomic coherences it has the advantage of being robust to dephasing effects such as small magnetic field inhomogeneities. The storage time is limited by the population lifetime of the ground states of the Λ system.