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We study the loss of spatial coherence in the extended wave function of fullerenes due to collisions with background gases. From the gradual suppression of quantum interference with increasing gas pressure we are able to support quantitatively both the predictions of decoherence theory and our picture of the interaction process. We thus explore the practical limits of matter wave interferometry at finite gas pressures and estimate the required experimental vacuum conditions for interferometry with even larger objects.PACS numbers: 03.65.Yz,39.20.+q Matter wave interferometers are based on quantum superpositions of spatially separated states of a single particle. However, as is well known, the concept of wave-particle duality does not apply to a classical object which by definition never occupies macroscopically distinct states simultaneously. By performing interference experiments with particles of increasing complexity one can therefore probe the borderline between these incompatible descriptions.It is still a matter of debate how to explain the quantum-to-classical transition in a unified framework. Some theories contain an element beyond the unitary evolution of quantum mechanics [1, 2] -which includes the 'collapse' of the wave function as taught in many standard textbooks. Decoherence theory, on the other hand, remains within the framework of the quantum theory [3,4,5]. It explains the decay of quantum coherences as being caused by the interaction of the quantum object with its environment.So far, several decoherence experiments in atom interferometry focused on the loss of coherence due to scattering of a single [6,7] or a few [8] laser photons by an atom. Other authors proposed or realized schemes to encode which-path information in internal atomic degrees of freedom, thereby reducing the interference contrast as well, in spite of a negligible change in the atomic centerof-mass state [9,10]. These studies are complemented by experiments which quantitatively followed the decoherence of a coherent photon state in a high-finesse microwave cavity [11] or of the motional state of a trapped ion [12]. However, all these experiments worked with few-level systems and engineered environments.In the present letter we quantitatively investigate a mechanism which seems to be among the most natural and most effective sources of decoherence in our macroscopic world, namely collisions with gas particles. From the controlled suppression of quantum interference as a function of the gas pressure we are able to test both the predictions of decoherence theory and our picture of the collisional interaction.We note that the effect of atomic collisions in an atom interferometer was already investigated in [13]. How- ever, decoherence effects were not observed in these experiments, since the detected atoms did not change the state of the colliding gas sufficiently to leave behind the required path information for decoherence. In contrast to that, our experiment uses massive C 70 -fullerene molecules, and is based on a Talbot-L...

We demonstrate quantum interference for tetraphenylporphyrin, the first biomolecule exhibiting wave nature, and for the fluorofullerene C60F48 using a near-field Talbot-Lau interferometer. For the porphyrins, which are distinguished by their low symmetry and their abundant occurence in organic systems, we find the theoretically expected maximal interference contrast and its expected dependence on the de Broglie wavelength. For C60F48 the observed fringe visibility is below the expected value, but the high contrast still provides good evidence for the quantum character of the observed fringe pattern. The fluorofullerenes therefore set the new mark in complexity and mass (1632 amu) for de Broglie wave experiments, exceeding the previous mass record by a factor of two.PACS numbers: 03.65.Ta,39.20.+q The wave-particle duality of massive objects is one of the corner stones of quantum physics. Nonetheless this quantum property is never observed in our everyday world. The current experiments are aiming at exploring the limits to which one can still observe the quantum wave nature of massive objects and to understand the role of the internal molecular structure and symmetry.Coherent molecule optics was already initiated as early as in 1930 when Estermann and Stern confirmed de Broglie's wave hypothesis [1] in a diffraction experiment with He atoms and H 2 molecules [2]. In contrast to the rapidly evolving field of electron and neutron optics, atom optics became only feasible about twenty years ago and has led from experiments with thermal atoms to coherent ensembles of ultra-cold atoms forming Bose-Einstein condensates. Molecule interferometry was only taken up again in 1994 with the first observation of Ramsey-Bordé interferences for I 2 [3] and with the proof of the existence of the weakly bound He 2 in a farfield diffraction experiment [4]. Experiments with alkali dimers in the far-field [5] and in near-field [6] interferometers followed. Recent interest in molecule optics has been stimulated by the quest for demonstrations of fundamental quantum mechanical effects with mesoscopic objects [7,8,9].In the present letter, we report the first demonstration of the wave nature of both tetraphenylporphyrin (TPP) and of fluorinated fullerenes using near-field interference. The porphyrin structure is at the heart of many complex biomolecules, serving as a color center for instance in chlorophyll and in hemoglobin. The fluorofullerene C 60 F 48 is the most massive (1632 amu) and most complex (composed of 108 atoms) molecule for which the de Broglie wave-nature has been shown so far (see fig.1).In order to demonstrate the wave property of a massive object with a short de Broglie wavelength it is advisable to use a near-field diffraction scheme. In particular a Talbot-Lau-interferometer (TLI, for details see [11,12,13,14]) is compact and rugged, has favorable3D Structure of tetraphenylporphyrin (TPP) C44H30N4 (left) and the fluorofullerene C60F48 (right) [10]. TPP (m=614 amu) is composed of four tilted phenyl rings attached t...

Context. The presence of two stellar populations in the Milky Way bulge has been reported recently, based on observations of giant and dwarf stars in the inner and intermediate bulge.Aims. We aim at studying the abundances and kinematics of stars in the outer Galactic bulge, thereby providing additional constraints on formation models of the bulge. Methods. Spectra of 401 red giant stars in a field at (l, b) = (0 • , −10 • ) were obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of luminosities down to below the two bulge red clumps are included in the data set. From these spectra we measured general metallicities, abundances of iron and the α-elements, and radial velocities of the stars. The abundances were derived from an interpolation and fitting procedure within a grid of COMARCS model atmospheres and spectra. These measurements as well as photometric data were compared to simulations with the Besançon and TRILEGAL models of the Galaxy. Results. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H] ∼ +0.3, comprising about 30% of the sample, with low velocity dispersion and low α-abundance, and ii) a metal-poor population at [M/H] ∼ −0.6 with high velocity dispersion and high α-abundance. The metallicity difference between the two populations, a systematically and statistically robust figure, is Δ[M/H] = 0.87 ± 0.03. The metal-rich population could be connected to the Galactic bar. We identify this population as the carrier of the double red clump feature. We do not find a significant difference in metallicity or radial velocity between the two red clumps, a small difference in metallicity being probably due to a selection effect and contamination by the metal-poor population. The velocity dispersion agrees well with predictions of the Besançon Galaxy model, but the metallicity of the "thick bulge" model component should be shifted to lower metallicity by 0.2 to 0.3 dex to well reproduce the observations. We present evidence that the metallicity distribution function depends on the evolutionary state of the sample stars, suggesting that enhanced mass loss preferentially removes metal-rich stars. We also confirm the decrease of α-element over-abundance with increasing metallicity. Conclusions. Our sample is consistent with the existence of two populations, one being a metal-rich bar, the second one being more like a metal-poor classical bulge with larger velocity dispersion.

We report the first spectroscopic identification of massive Galactic asymptotic giant branch (AGB) stars at the beginning of the thermal pulse (TP) phase. These stars are the most Li-rich massive AGBs found to date, super Li-rich AGBs with logε(Li)∼3-4. The high Li overabundances are accompanied by weak or no s-process element (i.e. Rb and Zr) enhancements. A comparison of our observations with the most recent hot bottom burning (HBB) and s-process nucleosynthesis models confirms that HBB is strongly activated during the first TPs but the 22 Ne neutron source needs many more TP and third dredge-up episodes to produce enough Rb at the stellar surface. We also show that the short-lived element Tc, usually used as an indicator of AGB genuineness, is not detected in massive AGBs which is in agreement with the theoretical predictions when the 22 Ne neutron source dominates the s-process nucleosynthesis.