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We report on the first production of an antihydrogen beam by charge exchange of 6.1 keV antiprotons with a cloud of positronium in the GBAR experiment at CERN. The antiproton beam was delivered by the AD/ELENA facility. The positronium target was produced from a positron beam itself obtained from an electron linear accelerator. We observe an excess over background indicating antihydrogen production with a significance of 3-4 standard deviations.

We present a description of the GBAR positron (e+) trapping apparatus, which consists of a three stage Buffer Gas Trap (BGT) followed by a High Field Penning Trap (HFT), and discuss its performance. The overall goal of the GBAR experiment is to measure the acceleration of the neutral antihydrogen (H) atom in the terrestrial gravitational field by neutralising a positive antihydrogen ion (H+), which has been cooled to a low temperature, and observing the subsequent H annihilation following free fall. To produce one H+ ion, about 10^10 positrons, efficiently converted into positronium (Ps), together with about 10^7 antiprotons (p), are required. The positrons, produced from an electron linac-based system, are accumulated first in the BGT whereafter they are stacked in the ultra-high vacuum HFT, where we have been able to trap 1.4(2) x 10^9 positrons in 1100 seconds.

We measure the colloidal interaction between two silica microspheres in aqueous solution in the distance range from $0.2\,\mu$m to $0.5\,\mu$m with the help of optical tweezers. When employing a sample with a low salt concentration, the resulting interaction is dominated by the repulsive double-layer interaction which is fully characterized. The double-layer interaction is suppressed when adding $0.22\,$M of salt to our sample, thus leading to a purely attractive Casimir signal. When analyzing the experimental data for the potential energy and force, we find good agreement with theoretical results based on the scattering approach. At the distance range probed experimentally, the interaction arises mainly from the unscreened transverse magnetic contribution in the zero-frequency limit, with nonzero Matsubara frequencies providing a negligible contribution. In contrast, such unscreened contribution is not included by the standard theoretical model of the Casimir interaction in electrolyte solutions, in which the zero-frequency term is treated separately as an electrostatic fluctuational effect. As a consequence, the resulting attraction is too weak in this standard model, by approximately one order of magnitude, to explain the experimental data. Overall, our experimental results shed light on the nature of the thermal zero-frequency contribution and indicate that the Casimir attraction across polar liquids has a longer range than previously predicted., Comment: 19 pages, 9 figures; updated references; added a detailed discussion of the subtraction procedure leading to the interaction potential

For the GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN's Antiproton Decelerator (AD) facility we have constructed a source of slow positrons, which uses a low-energy electron linear accelerator (linac). The driver linac produces electrons of 9 MeV kinetic energy that create positrons from bremsstrahlung-induced pair production. Staying below 10 MeV ensures no persistent radioactive activation in the target zone and that the radiation level outside the biological shield is safe for public access. An annealed tungsten-mesh assembly placed directly behind the target acts as a positron moderator. The system produces $5\times10^7$ slow positrons per second, a performance demonstrating that a low-energy electron linac is a superior choice over positron-emitting radioactive sources for high positron flux., Comment: published in NIM A. 33 pages 9 figures

Observation time is the key parameter for improving the precision of measurements of gravitational quantum states of particles levitating above a reflecting surface. We propose a new method of long confinement in such states of atoms, anti-atoms, neutrons and other particles possessing a magnetic moment. The Earth gravitational field and a reflecting mirror confine particles in the vertical direction. The magnetic field originating from electric current passing through a vertical wire confines particles in the radial direction. Under appropriate conditions, motions along these two directions are decoupled to a high degree. We estimate characteristic parameters of the problem, and list possible systematic effects that limit storage times due to the coupling of the two motions. In the limit of low particle velocities and magnetic fields, precise control of the particle motion and long storage times in the trap can provide ideal conditions for both gravitational, optical and hyperfine spectroscopy: for the sensitive verification of the equivalence principle for antihydrogen atoms; for increasing the accuracy of optical and hyperfine spectroscopy of atoms and antiatoms; for improving constraints on extra fundamental interactions from experiments with neutrons, atoms and antiatoms.

We apply the scattering approach to the Casimir interaction between two dielectric half-spaces separated by an electrolyte solution. We take the nonlocal electromagnetic response of the intervening medium into account, which results from the presence of movable ions in solution. In addition to the usual transverse modes, we consider longitudinal channels and their coupling by reflection at the surface of the local dielectric. The Casimir interaction energy is calculated from the matrix describing a round-trip of coupled transverse and longitudinal waves between the interacting surfaces. The nonzero-frequency contributions are approximately unaffected by the presence of ions. We find, at zero frequency, a contribution from longitudinal channels, which is screened over a distance of the order of the Debye length, alongside an unscreened term arising from transverse-magnetic modes. The latter defines the long-distance asymptotic limit for the interaction., Comment: 9 pages, 3 figures

We measured the temperature dependence of the probability of small heating and total losses of UCNs on the PFPE Fomblin Y surface with various molecular masses Mw=2800, 3300, 6500 amu in the temperature range of 100-300 K. The probability of small heating sharply decreases with increasing Mw and decreasing temperature. The probability of total loss weakly decreases with decreasing temperature and takes the minimum value at Mw=3300 amu. As this oil provides a homogeneous surface with minimal probabilities of small heating and total losses of UCNs, it is the preferred candidate for experiments on measuring the neutron lifetime.

We propose to use quantum interferences to improve the accuracy of the measurement of the free fall acceleration g of antihydrogen in the GBAR experiment. This method uses most antiatoms prepared in the experiment and it is simple in its principle as interferences between gravitational quantum states are readout without transitions between them. We use a maximum likelihood method for estimating the value of g and assess the accuracy of this estimation by a Monte-Carlo simulation. We find that the accuracy is improved by approximately three orders of magnitude with respect to the classical timing technique planned for the current design of the experiment., Comment: 8 figures

We take dissipation into account in the derivation of the Casimir energy formula between two objects placed in a surrounding medium. The dissipation channels are considered explicitly in order to take advantage of the unitarity of the full scattering processes. We demonstrate that the Casimir energy is given by a scattering formula expressed in terms of the scattering amplitudes coupling internal channels and taking dissipation into account in an implicit way. We prove that this formula is also valid when the surrounding medium is dissipative., Comment: 11 pages, 4 figures

We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liquid helium film. The Casimir-Polder potential and quantum reflection are calculated for different thicknesses of the film supported by different substrates. Antihydrogen can be protected from anni- hilation for as long as 1.3s on a bulk of liquid 4He, and 1.7s for liquid 3He. These large lifetimes open interesting perspectives for spectroscopic measurements of the free fall acceleration of antihydrogen. Variation of the scattering length with the thickness of a film of helium shows interferences which we interpret through a Liouville transformation of the quantum reflection problem.

We present an underground long baseline atom interferometer to study gravity at large scale. The hybrid atom-laser antenna will use several atom interferometers simultaneously interrogated by the resonant mode of an optical cavity. The instrument will be a demonstrator for gravitational wave detection in a frequency band (100 mHz - 1 Hz) not explored by classical ground and space-based observatories, and interesting for potential astrophysical sources. In the initial instrument configuration, standard atom interferometry techniques will be adopted, which will bring to a peak strain sensitivity of 2$\cdot 10^{-13}/\sqrt{\mathrm{Hz}}$ at 2 Hz. The experiment will be realized at the underground facility of the Laboratoire Souterrain \`a Bas Bruit (LSBB) in Rustrel--France, an exceptional site located away from major anthropogenic disturbances and showing very low background noise. In the following, we present the measurement principle of an in-cavity atom interferometer, derive signal extraction for Gravitational Wave measurement from the antenna and determine the expected strain sensitivity. We then detail the functioning of the different systems of the antenna and describe the properties of the installation site.

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schr\"odinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting respectively as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose a new approximate treatment which is precise enough to discuss spectroscopy experiments aiming at tests of the weak equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances., Comment: Accepted in PRA

We performed precision measurements of the probability of small heating and spectrum of UCNs up-scattered on the surface of hydrogen-free oil Fomblin Y-HVAC 18/8 as a function of temperature. The probability is well reproducible, does not depend on sample thickness and does not evolve in time. It is equal (9.8+-0.2)10^(-6) at the ambient temperature. The spectrum coincides with those measured with solid-surface and nanoparticle samples. Indirect arguments indicate that spectrum shape weakly depends on temperature. Measured experimental data can be satisfactory described both within the model of near-surface nanodroplets and the model of capillary waves.

We reply to the "Comment on 'The Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors'" [arXiv:1604.06432]. We believe the comment misrepresents our papers, and fails to provide a plausible resolution to the conflict between theory and experiment., Comment: To appear in Phys. Rev. E

In this paper we describe the architecture of a Platform as a Service (PaaS) oriented to computing and data analysis. In order to clarify the choices we made, we explain the features using practical examples, applied to several known usage patterns in the area of HEP computing. The proposed architecture is devised to provide researchers with a unified view of distributed computing infrastructures, focusing in facilitating seamless access. In this respect the Platform is able to profit from the most recent developments for computing and processing large amounts of data, and to exploit current storage and preservation technologies, with the appropriate mechanisms to ensure security and privacy., Comment: 31 pages, 12 Figures

We study an effect of quenching of antihydrogen quantum states near material surface in the gravitational field of the Earth by local charges randomly distributed along the mirror surface. The quenching mechanism reduces the quantum reflection probability because of additional atom-charge interaction and nonadiabatic transitions to excited gravitational states. Our approach is suitable for accounting for quenching caused by any kind of additional interaction with the characteristic range much smaller than the typical gravitational state wave-length.

We study an interferometric approach to measure gravitational mass of antihydrogen. The method consists of preparing a coherent superposition of antihydrogen quantum state localized near a material surface in the gravitational field of the Earth, and then observing the time distribution of annihilation events followed after the free fall of an initially prepared superposition from a given height to the detector plate. We show that a corresponding time distribution is related to the momentum distribution in the initial state that allows its precise measurement. This approach is combined with a method of production of a coherent superposition of gravitational states by inducing a resonant transition using oscillating gradient magnetic field. We estimate an accuracy of measuring the gravitational mass of antihydrogen atom which could be deduced from such a measurement., Comment: arXiv admin note: text overlap with arXiv:1403.4783

We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic plane mirrors. As in the previously studied case of non-magnetic materials (Guerout et al, Phys. Rev. E 90 042125), we recover the usual expression for the lossy model of optical response, but not for the lossless plasma model. We also show that the modes associated with the Foucault currents play a crucial role in the limit of vanishing losses, in contrast to expectations.

We investigate in detail the Casimir torque induced by quantum vacuum fluctuations between two nanostructured plates. Our calculations are based on the scattering approach and take into account the coupling between different modes induced by the shape of the surface which are neglected in any sort of proximity approximation or effective medium approach. We then present an experimental setup aiming at measuring this torque., Comment: 7 pages, 7 figures

The present notes are organized as the lectures given at the Les Houches Summer School "Quantum Optics and Nanophotonics" in August 2013. The first section contains an introduction and a description of the current state-of-the-art for Casimir force measurements and their comparison with theory. The second and third sections are a pedagogical presentation of the main features of the theory of Casimir forces for 1-dimensional model systems and for mirrors in 3-dimensional space., Comment: Notes corresponding to the lectures given at Les Houches 101th summer school, August 2013. To appear in the proceedings "Quantum Optics and Nanophotonics", to be published by Oxford University Press

Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure $P_{\rm res}(D)$ in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. Within this framework, and assuming that the potential distribution does not vary significantly at low pressure, the calculated $P_{\rm res}(D)$ does not explain the magnitude or the separation dependence of the difference $\Delta P (D)$ between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au., Comment: 8 pages, 3 figures. Updated conclusions. Version to appear in Phys. Rev. A

We carefully re-examine the conditions of validity for the consistent derivation of the Lifshitz-Matsubara sum formula for the Casimir pressure between metallic plane mirrors. We recover the usual expression for the lossy Drude model, but not for the lossless plasma model. We give an interpretation of this new result in terms of the modes associated with the Foucault currents which play a role in the limit of vanishing losses, in contrast to common expectations., Comment: Accepted in Phys. Rev. E

We study a method to induce resonant transitions between antihydrogen ($\bar{H}$) quantum states above a material surface in the gravitational field of the Earth. The method consists of applying a gradient of magnetic field, which is temporally oscillating with the frequency equal to a frequency of transition between gravitational states of antihydrogen. A corresponding resonant change in the spatial density of antihydrogen atoms could be measured as a function of the frequency of applied field. We estimate an accuracy of measuring antihydrogen gravitational states spacing and show how a value of the gravitational mass of the $\bar{H}$ atom could be deduced from such a measurement. We also demonstrate that a method of induced transitions could be combined with a free-fall-time measurement in order to further improve the precision.

In this communication, we focus on the possibility to test General Relativity (GR) with radioscience experiments. We present simulations of observables performed in alternative theories of gravity using a software that simulates Range/Doppler signals directly from the space time metric. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity (PEG) and with Standard Model Extension (SME)., Comment: 3 pages, 1 figure, proceedings of 13th Marcel Grossmann Meeting, v2: minor changes

We study quantum reflection of antihydrogen atoms from matter slabs due to the van der Waals/Casimir-Polder (vdW/CP) potential. By taking into account the specificities of antihydrogen and the optical properties and width of the slabs we calculate realistic estimates for the potential and quantum reflection amplitudes. Next we discuss the paradoxical result of larger reflection coefficients estimated for weaker potentials in terms of the Schwarzian derivative. We analyze the limiting case of reflections at small energies, which are characterized by a scattering length and have interesting applications for trapping and guiding antihydrogen using material walls.

We study quantum reflection of antihydrogen atoms from nanoporous media due to the Casimir-Polder (CP) potential. Using a simple effective medium model, we show a dramatic increase of the probability of quantum reflection of antihydrogen atoms if the porosity of the medium increases. We discuss the limiting case of reflections at small energies, which have interesting applications for trapping and guiding antihydrogen using material walls.

We present detailed calculations for the Casimir force between a plane and a nanostructured surface at finite temperature in the framework of the scattering theory. We then study numerically the effect of finite temperature as a function of the grating parameters and the separation distance. We also infer non-trivial geometrical effects on the Casimir interaction via a comparison with the proximity force approximation. Finally, we compare our calculations with data from experiments performed with nanostructured surfaces.

Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nano-droplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing small heating of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there., Comment: 5 pages, 4 figures

Patch potentials arising from the polycrystalline structure of material samples may contribute significantly to measured signals in Casimir force experiments. Most of these experiments are performed in the sphere-plane geometry, yet, up to now all analysis of patch effects has been taken into account using the proximity force approximation which, in essence, treats the sphere as a plane. In this paper we present the exact solution for the electrostatic patch interaction energy in the sphere- plane geometry, and derive exact analytical formulas for the electrostatic patch force and minimizing potential. We perform numerical simulations to analyze the distance dependence of the minimizing potential as a function of patch size, and quantify the sphere-plane patch force for a particular patch layout. Once the patch potentials on both surfaces are measured by dedicated experiments our formulas can be used to exactly quantify the sphere-plane patch force in the particular experimental situation., Comment: 13 pages, 4 figures

We present a theoretical study of radiative heat transfer between dielectric nanogratings in the scattering approach. As a comparision with these exact results, we also evaluate the domain of validity of Derjaguin's Proximity Approximation (PA). We consider a system of two corrugated silica plates with various grating geometries, separation distances, and lateral displacement of the plates with respect to one another. Numerical computations show that while the PA is a good approximation for aligned gratings, it cannot be used when the gratings are laterally displaced. We illustrate this by a thermal modulator device for nanosystems based on such a displacement.

Physical adsorption of atoms, molecules and clusters on surface is known. It is linked to many phenomena in physics, chemistry, and biology. Usually the studies of adsorption are limited to the particle sizes of up to ~10^2-10^3 atoms. Following a general formalism, we apply it to even larger objects and discover qualitatively new phenomena. A large particle is bound to surface in a deep and broad potential well formed by van der Waals/ Casimir-Polder forces. The well depth is significantly larger than the characteristic thermal energy. Nanoparticles in high-excited bound states form two-dimensional gas of objects quasi-freely traveling along surface. A particularly interesting prediction is small-energy-transfer scattering of UCN on solid/ liquid surfaces covered by such levitating nanoparticles/ nano-droplets. The change in UCN energy is due to the Doppler shift induced by UCN collisions with nanoparticles; the energy change is about as small as the UCN initial energy. We compare theoretical estimations of our model to all relevant existing data and state that they agree quite well. As our theoretical formalism provides robust predictions and the experimental data are rather precise, we conclude that the recently discovered intriguing phenomenon of small heating of UCN in traps is due to their collisions with such levitating nanoparticles. Moreover, this new phenomenon might be relevant to the striking contradiction between results of the neutron lifetime measurements with smallest reported uncertainties as it might cause major false effects in these experiments; thus it affects fundamental conclusions concerning precision checks of unitarity of the Cabibbo-Kobayashi-Maskawa matrix, cosmology, astrophysics. Dedicated measurements of UCN up-scattering on specially prepared surfaces and nanoparticles levitating above them might provide a unique method to study surface potentials., Comment: 20 pages, 12 figures

We compute the radiative heat transfer between nanostructured gold plates in the framework of the scattering theory. We predict an enhancement of the heat transfer as we increase the depth of the corrugations while keeping the distance of closest approach fixed. We interpret this effect in terms of the evolution of plasmonic and guided modes as a function of the grating's geometry.

In this paper, we focus on the possibility to test General Relativity in the Solar System with radioscience measurements. To this aim, we present a new software that simulates Range and Doppler signals directly from the space-time metric. This flexible approach allows one to perform simulations in General Relativity and in alternative metric theories of gravity. In a second step, a least-squares fit of the different initial conditions involved in the situation is performed in order to compare anomalous signals produced by a given alternative theory with the ones obtained in General Relativity. This software provides orders of magnitude and signatures stemming from hypothetical alternative theories of gravity on radioscience signals. As an application, we present some simulations done for the Cassini mission in Post-Einsteinian Gravity and in the context of MOND External Field Effect. We deduce constraints on the Post-Einsteinian parameters but find that the considered arc of the Cassini mission is not useful to constrain the MOND External Field Effect., Comment: 27 pages, 7 figures, minor changes, accepted version

We study theoretically interference of the long-living quasistationary quantum states of antihydrogen atoms, localized near a concave material surface. Such states are an antimatter analog of the whispering gallery states of neutrons and matter atoms, and similar to the whispering gallery modes of sound and electro-magnetic waves. Quantum states of antihydrogen are formed by the combined effect of quantum reflection from van der Waals/Casimir-Polder (vdW/CP) potential of the surface and the centrifugal potential. We point out a method for precision studies of quantum reflection of antiatoms from vdW/CP potential; this method uses interference of the whispering gallery states of antihydrogen., Comment: 13 pages 7 figures

The laws of gravitation have been tested for a long time with steadily improving precision, leading at some moment of time to paradigmatic evolutions. Pursuing this continual effort is of great importance for science. In this communication, we focus on Solar System tests of gravity and more precisely on possible tests that can be performed with radio science observations (Range and Doppler). After briefly reviewing the current tests of gravitation at Solar System scales, we give motivations to continue such experiments. In order to obtain signature and estimate the amplitude of anomalous signals that could show up in radio science observables because of modified gravitational laws, we developed a new software that simulates Range/Doppler signals. We present this new tool that simulates radio science observables directly from the space-time metric. We apply this tool to the Cassini mission during its cruise from Jupiter to Saturn and derive constraints on the parameters entering alternative theories of gravity beyond the standard Parametrized Post Newtonian theory., Comment: proceedings of SF2A 2011 - minor changes (typos corrected - references updated)

Electrostatic patch potentials give rise to forces between neutral conductors at distances in the micrometer range and must be accounted for in the analysis of Casimir force experiments. In this paper we develop a quasi-local model for describing random potentials on metallic surfaces. In contrast to some previously published results, we find that patches may provide a significant contribution to the measured signal, and may render the experimental data at distances below 1 micrometer compatible with theoretical predictions based on the Drude model., Comment: 9 pages, 6 figures, version 2 includes corrections to the text and added references. Version 3 contains modified figures and text. Version 4 contains modified figures and text

The predictions of General relativity (GR) are in good agreement with observations in the solar system. Nevertheless, unexpected anomalies appeared during the last decades, along with the increasing precision of measurements. Those anomalies are present in spacecraft tracking data (Pioneer and flyby anomalies) as well as ephemerides. In addition, the whole theory is challenged at galactic and cosmic scales with the dark matter and dark energy issues. Finally, the unification in the framework of quantum field theories remains an open question, whose solution will certainly lead to modifications of the theory, even at large distances. As long as those "dark sides" of the universe have no universally accepted interpretation nor are they observed through other means than the gravitational anomalies they have been designed to cure, these anomalies may as well be interpreted as deviations from GR. In this context, there is a strong motivation for improved and more systematic tests of GR inside the solar system, with the aim to bridge the gap between gravity experiments in the solar system and observations at much larger scales. We review a family of metric extensions of GR which preserve the equivalence principle but modify the coupling between energy and curvature and provide a phenomenological framework which generalizes the PPN framework and "fifth force" extensions of GR. We briefly discuss some possible observational consequences in connection with highly accurate ephemerides., Comment: Proceedings of Journ\'ees 2010 "Syst\`emes de r\'ef\'erence spatio-temporels", New challenges for reference systems and numerical standards in astronomy

We study how quantum correlations survive at large scales in spite of their exposition to stochastic backgrounds of gravitational waves. We consider Einstein-Podolski-Rosen (EPR) correlations built up on the polarizations of photon pairs and evaluate how they are affected by the cosmic gravitational wave background (CGWB). We evaluate the quantum decoherence of the EPR correlations in terms of a reduction of the violation of the Bell inequality as written by Clauser, Horne, Shimony and Holt (CHSH). We show that this decoherence remains small and that EPR correlations can in principle survive up to the largest cosmic scales., Comment: 5 figures