We have observed the decoherence of a lithium atomic wave during its propagation in the presence of the radiation emitted by tungsten-halogen lamps, i.e., decoherence induced by blackbody radiation. We used our atom interferometer to detect this decoherence by measuring the atom fringe-visibility loss. The absorption of a photon excites the atom, which spontaneously emits a fluorescence photon. The momenta of these two photons have random directions, and this random character is the main source of decoherence. All previous similar experiments used small-bandwidth coherent excitation by a laser, whereas incoherent radiation involves several technical and conceptual differences. Our approach is interesting as blackbody radiation is omnipresent and decoherence should be considered if particles resonant to electromagnetic fields are used.

We provide a comprehensive study of ultra-cold atom diffraction by an optical lattice. We focus on an intermediate regime between the Raman-Nath and the Bragg regimes, the so-called quasiBragg regime. The experimental results are in a good agreement with a full numerical integration of the Schrödinger equation. We investigate the long pulse regime limited by a strong velocity selection and the short pulse regime limited by ”non-adiabatic losses”. For each of these regimes, we estimate the multi-port features of the Bragg interferometers. Finally, we discuss the best compromise between these two regimes, considering the diffraction phase shift and the existence of parasitic interferometers.

In 1851, Stokes calculated the force exerted by a viscous fluid on an infinite cylinder in oscillating motion. Although the calculation was restricted to vanishingly small Reynolds numbers Re, most of the experimental tests performed up to now have been made with Re 1. Here we present a series of experiments involving a cylindrical pendulum oscillating in air at different pressures and with Re < 1. We deduce the unsteady friction force from the measurement of the damping time of the oscillations. We compare our experimental results for the unsteady force (a) to Stokes' predictions for an infinite cylinder and (b) to predictions for finite-length cylinders, using an expression of the unsteady force derived from the works of Lawrence and Weinbaum and Loewenberg. The agreement is quite satisfactory and proves that macroscopic objects like a pendulum can be used as probes of the Stokesian flow regime.

We have measured the tune-out wavelength of lithium isotope Li-7 at 671 nm. We have used our atom interferometer to measure the phase shift due to the dynamical Stark effect as a function of the laser frequency when a laser beam was focused on a single interferometer arm. The tune-out wavelength is a function of the hyperfine F, m(F) sublevel, and we have prepared the atoms in the sublevel F = 2, m(F) = +2 or -2. We find that the tune-out frequency of the F = 2, m(F) = +2 sublevel is at 3388(8)MHz to the blue of the S-2(1/2,) F =1 -> P-2(1/2), F' = 2 transition, the accuracy of this measurement being limited by imperfect optical pumping. This measurement is in excellent agreement with its theoretical value, and, once corrected for different tensorial contributions, our measurement agrees with the more precise measurement of Copenhaver et al. [Phys. Rev. A 100, 063603 (2019)], who also used atom interferometry but different experimental conditions.

When atoms or molecules exist in the form of stable negative ions, they play a crucial role in the gas phase chemistry. Determining the existence of such an ion, its internal energy and its stability are necessary prerequisites to analyze the role of this ion in a particular medium. Experimental evidence of the existence of a negative methane ion CH$_4^-$ has been provided over a period of 50 years. However, quantum chemistry had not been able to explain its existence, and a detailed recent study has shown that the experimentally observed species cannot be described by the attachement of an electron in the ground state of CH$_4^-$. Here we describe CH$_4^-$ as being a metastable species in its lowest quartet spin state and we find that this species is a CH$_2^-$-:H$_2$ exciplex with three open shells, lying 5.8 eV above the methane singlet ground state but slightly below the dissociation fragments. The formation of charged exciplexes is a novel mechanism to explain small molecular anions with implications in a plethora of basic and applied research fields.

Stokes calculated the force exerted by the surrounding fluid on a sphere and on a cylinder in oscillating motion. Although these results are valid only if the Reynolds number Re is very small, $${\text {Re}}\ll 1$$, all the tests on macroscopic spheres have been made with Re larger than 20. Here, we describe an experiment which measures the drag force on an oscillating sphere with small values of the Reynolds number, down to $${\text {Re}}\approx 0.03$$ for the smallest sphere studied here while the Stokes number St is large, between 150 and 1500. Our measurements are in very good agreement with Stokes’ result, and in particular, they exhibit the quadratic dependence of the force with the sphere radius when this radius is larger than the viscous penetration depth $$\delta$$.

The Pancharatnam phase belongs to the family of geometric Berry phases. We use this optical phase to control the phase of our atom interferometer, which involves diffraction of the atom wave by laser standing waves in the Bragg regime. The Pancharatnam phase of the reflected beam of one standing wave controls the phase imprinted on the atom wave by the diffraction process. In addition to the expected phase shift, the experimental data exhibits the signature of several defects which are described and quantified. From this analysis, we estimate that a Pancharatnam phase shifter can be reliably used to control the phase of an atom interferometer in the sub-mrad regime. Moreover, as the geometric nature of the Pancharatnam phase renders this phase achromatic, its use in multispecies atom interferometers may be of great interest.

A phase modulation puts the atom in a coherent superposition of quantum states with different kinetic energies. We have detected the interference of such modulated waves at the output of our atom interferometer, and we have observed beats at the difference of the modulation frequencies and its harmonics, in good agreement with theory. The phase modulations were produced by a Kerr phase modulator, i.e., by the propagation of the atom wave in a time-dependent electric field. An extension of this technique to electron interferometry should open the way to very high temporal resolution in electron microscopy.

In the present paper, we first explain how atom interferometry can be used to measure weak perturbations and the need of a separated-arm atom interferometer for such experiments. We then describe our atom interferometer and we illustrate the measurement of weak perturbations by two examples. The first one is the measurement of electric polarizability of atoms, which is an example of a dynamical phase shift. The second example is the first measurement of the He-McKellar-Wilkens (HMW) phase: this phase appears when an electric dipole propagates in a transverse magnetic field and it is the third electromagnetic geometric phase, after the Aharonov-Bohm and Aharonov-Casher phases.

We have recently tested the topological phase predicted by He and McKellar and by Wilkens: this phase appears when an electric dipole propagates in a transverse magnetic field. In the present paper, we first recall the physical origin of this phase and its relations to the Aharonov-Bohm and Aharonov-Casher phases. We then explain possible detection schemes and we briefly describe the lithium atom interferometer we have used for this purpose. Finally, we analyze in great detail the phase shifts induced by electric and magnetic fields acting on such an interferometer, taking into account experimental defects. The experiment and its results are described in the following paper.

In this Letter, we report a measurement of the He-McKellar-Wilkens (HMW) topological phase by atom interferometry. The experiment is done with our lithium atom interferometer, and in order to suppress the stray effects present in our first experiment, we use optical pumping of the (7)Li atoms in their F=2, m(F)=+2 (or -2) ground state sublevel. In these conditions, the measured phase shift is the sum of the HMW phase and of the Aharonov-Casher phase, which are separated due to their different m(F) dependence. The HMW phase has been measured for different lithium beam velocities and the results are in very good agreement with a phase independent of the atom velocity, as expected for a topological phase.

We have developed and characterized a heat pipe for lithium spectroscopy, which is cooled only by air-convection, although its operating temperature is 330 °C: its construction is simple, of moderate cost and it is very reliable. A thermal model proves that heat-pipes without water cooling can be used up to considerably higher temperatures.

We describe measurements of the He-McKellar-Wilkens (HMW) and Aharonov-Casher (AC) topological phases by atom interferometry. These two phases are measured in a single experiment with our lithium atom interferometer [1]. The interferometer arms spatial separation (about 100 micrometers) is sufficient to apply opposite electric fields on the two arms. In order to suppress stray effects present in our first experiment [2], we optically pump the Li atoms in their F=2, mF=+2 (or -2) ground state sublevel. The measured phase shift is the sum of the HMW phase and of the AC phase: we separate these two contributions thanks to their different mF-dependence. Both phases have been measured for different lithium beam velocities and the results are independent of the atom velocity, as expected for topological phases. Figure 1 presents our results for the HMW phase.

We report an experimental test of the topological phase predicted by He and McKellar in 1993 and by Wilkens in 1994: this phase, which appears when an electric dipole propagates in a magnetic field, is connected to the Aharonov-Casher effect by electric-magnetic duality. The He-McKellar-Wilkens phase is quite small, at most 27 mrad in our experiment, and this experiment requires the high phase sensitivity of our atom interferometer with spatially separated arms as well as symmetry reversals such as the direction of the electric and magnetic fields. The measured value of the He-McKellar-Wilkens phase differs by 31% from its theoretical value, a difference possibly due to some as yet uncontrolled systematic errors.

We present an all solid-state narrow line-width laser source emitting $670\,\mathrm{mW}$ output power at $671\,\mathrm{nm}$ delivered in a diffraction-limited beam. The \linebreak source is based on a fre-quency-doubled diode-end-linebreak pumped ring laser operating on the ${^4F}_{3/2} \rightarrow {^4I}_{13/2}$ transition in Nd:YVO$_4$. By using periodically-poled po-tassium titanyl phosphate (ppKTP) in an external build-up cavity, doubling efficiencies of up to 86% are obtained. Tunability of the source over $100\,\rm GHz$ is accomplished. We demonstrate the suitability of this robust frequency-stabilized light source for laser cooling of lithium atoms. Finally a simplified design based on intra-cavity doubling is described and first results are presented.

Using a nano-scale grid as a phase-shifting component, an atom interferometer has beenutilized to study atom-surface van der Waals (VdW) interactions. We report phase shifts onthe order of 0.2 rad, with a few percent uncertainty. We also report thevelocity-dependent attenuation of atomic de Broglie wave amplitude that occurs inconjunction with the observed phase shifts. From these data we deduce the strength of theVdW potential and its dependence on the atom-surface separation. We discuss how ourmeasurements can be used to set limits on the strength of non-Newtonian gravity at shortlength scales and we discuss the possibility of measuring the atom-surface interactionsover a larger range of atom-surface distances. We also compare our results to severaltheoretical predictions for the VdW potential of Li near a variety of surfaces.

We summarise the scientific and technological aspects of the Search for Anomalous Gravitation using Atomic Sensors (SAGAS) project, submitted to ESA in June 2007 in response to the Cosmic Vision 2015–2025 call for proposals. The proposed mission aims at flying highly sensitive atomic sensors (optical clock, cold atom accelerometer, optical link) on a Solar System escape trajectory in the 2020 to 2030 time-frame. SAGAS has numerous science objectives in fundamental physics and Solar System science, for example numerous tests of general relativity and the exploration of the Kuiper belt. The combination of highly sensitive atomic sensors and of the laser link well adapted for large distances will allow measurements with unprecedented accuracy and on scales never reached before. We present the proposed mission in some detail, with particular emphasis on the science goals and associated measurements and technologies.

In response to ESA’s Call for proposals of 5 March 2007 of the COSMIC VISION 2015–2025 plan of the ESA science programme, we propose a M-class satellite mission to test of the Equivalence Principle in the quantum domain by investigating the extended free fall of matter waves instead of macroscopic bodies as in the case of GAUGE, MICROSCOPE or STEP. The satellite, called Matter Wave Explorer of Gravity, will carry an experiment to test gravity, namely the measurement of the equal rate of free fall with various isotopes of distinct atomic species with precision cold atom interferometry in the vicinity of the earth. This will allow for a first quantum test the Equivalence Principle with spin polarised particles and with pure fermionic and bosonic atomic ensembles. Due to the space conditions, the free fall of Rubidium and Potassium isotopes will be compared with a maximum accelerational sensitivity of 5·10 − 16 m/s2 corresponding to an accuracy of the test of the Equivalence Principle of 1 part in 1016. Besides the primary scientific goal, the quantum test of the Equivalence Principle, the mission can be extended to provide additional information about the gravitational field of the earth or for testing theories of fundamental processes of decoherence which are investigated by various theory groups in the context of quantum gravity phenomenology. In this proposal we present in detail the mission objectives and the technical aspects of the proposed mission.

We used the Toulouse atom interferometer to study how Van der Waals (VdW) interactions between atoms and surfaces cause velocity-dependent phase shifts for atomic de Broglie waves. By introducing a thin nano-grating in one branch of this interferometer, we observed a phase shift that depends on velocity to the power −0.49. This dispersion serves to measure both the strength and the position dependence of the atom-surface potential in the range from 5 to 10 nm from the surface, and it can also set new limits on non-Newtonian gravity in the 2 nm range.