J. Baudon

Atomic Interferometry with Metastable Hydrogen Atoms

An atomic interferometer using the longitudinal Stern-Gerlach effect has been constructed. A thermal beam of metastable hydrogen atoms has been used to test the apparatus. Interference patterns have been obtained. The visibility of the fringes is limited by the velocity spread of the beam. The observed patterns are in good agreement with that predicted from the actual velocity distribution.

Optical potentials for Ne*(3P2,0)-Ar, N2 interactions

The differential elastic cross sections for Ne*(3P2,0)–Ar and Ne*(3P2,0)–N2 collisions have been measured in crossed beam experiments at 0.064 and 0.318 and at 0.071 and 0.295 eV, collision energies, respectively. These results have been analyzed simultaneously with integral cross sections and total ionization cross sections already available and optical spherical potentials for these two systems have been obtained. These potentials appear to be rather accurate in the distance range from 2.5 to ∼9 and from 3.0 to ∼9 A for Ne*–Ar and Ne*–N2, respectively. The well depths and equilibrium distances are 5.12 meV and 4.9 A for Ne*–Ar and 3.56 meV and 5.40 A for Ne*–N2. The short‐range repulsion in both cases exhibits a change in slope which can be correlated with the influence, for the interaction at shorter distances, of the Ne+ core of the metastable atom, which becomes less effective when the intermolecular distance increases. The optical potentials proposed here are given in analytical form suitable for th...

Negative-index media for matter-wave optics.

We consider the extension of optical metamaterials to matter waves and then the down scaling of metaoptics to nanometric wavelengths. We show that the generic property of pulsed comoving magnetic fields allows us to fashion the wave-number dependence of the atomic phase shift. It can be used to produce a transient negative group velocity of an atomic wave packet, which results into a negative refraction of the matter wave. Application to slow metastable argon atoms Ar(3P2) shows that the device is able to operate either as an efficient beam splitter or an atomic metalens.

Geometrical Phase Factor for a Non-Hermitian Hamiltonian

In a previous paper, the measurement of an atomic Berry phase associated with two crossing levels has been suggested as a possible test for an atomic interferometry method. As one of the two levels involved is radiative, an analysis of geometrical phase factor arising in the cyclic evolution of a non-Hermitian Hamiltonian is undertaken here. It is shown that the use of the dual basis allows a simple generalization of Berrys results and that, in addition to the two possible values encountered in the Hermitian case (0, π), the geometrical phase can take on as intermediate value π/2 or even a complex value, whereas the corresponding quantum states may be permuted. The validity of the adiabatic approximation is discussed in view of the measurability of this new effect.

Ultra thin coherent atom beam by Stern-Gerlach interferometry

It is demonstrated that a Stern-Gerlach interferometer including a special transverse phase shifter can generate an atomic beam of a small diameter (few tens of nm). Calculations carried out in a coherent regime confirm this point. They also show that the device is almost insensitive to velocity dispersion and that the required mechanical accuracy is quite accessible. Due to the peculiar transverse amplitude distribution (of the Lorentz type), the spreading of the generated beam profile is very small compared to that given by a circular diaphragm or a Gaussian profile of comparable initial diameter. This is a key property as regards applications, e.g. in atom lithography and surface probing.

Optical properties of metallic nanowires

The optical response of metallic nanowires is determined taking into account the non-local electron response by use of a self-consistent method and a jellium model. An exact formula for the reflection factor is obtained in the usual case of an hydrodynamic dielectric function. Up to a constant factor it coincides with the non-retarded limit of the amplitude obtained in a previous calculation, leading finally to the same extinction function. This function is calculated for certain metallic nanowires of experimental interest (Na, Ag). From the non-retarded near field response, the scattering amplitude at any distance can be derived.

Polarization effects in metastable neon atom (Ne* (3P2)) on ground state neon atom collision at thermal energy

Abstract The difference Δ between the differential cross section for Ne*( 3 P 2 atoms polarized either in state | j =2, m =+2 > or | j =2, m =−2 >, colliding at thermal energy with a groundstate target (Ne,O 2 ), is measured. In the symmetric case Ne*-Ne, direct and exchange contribution are observed. General properties of Δ, derived from symmetry considerations, are established; in particular: (i) the interference character of Δ, (ii) the role played by the azimuthal dependence of the scattering amplitudes, (iii) the property Δ(0) = Δ(180°)=0. The relationship between the Fourier harmonics introduced in this discussion and the scattering amplitudes used in standard collision treatments are given.

The low energy collision between metastable Ne*(3P0,2) and He(1S0): ab initio potentials, differential cross sections and polarization effects

Potential energies for molecular states dissociating into Ne*(1P1,3P0,1,2) + He(1S0) have been calculated ab initio within the distance range 4–100a0. The SCF energy (without spin-orbit interaction) is optimized on the lowest3Σ state. After CI, the four Λ-states (1,3Σ,1,3Π)are obtained. They dissociate into Ne*(1,3P) + He(1S). All of them are repulsive atR ≲ 8a0, they exhibit shallow wells around 12a0 and have a correct asymptotic behaviour (∼ -R−6). The spin-orbit interaction is introduced, using the Cohen-Schneider scheme, and adiabatic Ω-potentials are derived. The collision at low energy (E ≦ 124 meV) is described in the frame of a fragment-state basis. By means of a deflation procedure, it is shown that states dissociating into Ne*(1P1) + He can be eliminated, which lead to a 9 × 9 interaction matrix dynamically equivalent to the original 12 × 12 matrix, in the subspace of interest. Collision channels are defined by angular momenta,J (total),j (of Ne*) andl (of the relative motion). Scattering radial equations are solved by the algorithm of Gordon and theS matrix is derived. Two sets of physically meaningful scattering amplitudes (and differential cross sections) are constructed, referred to the incident axis or to the initial and final directions of the internuclear axis. Polarization effects are discussed. The case of a quantization axis perpendicular to the collision plane is also mentioned.

Theory of One-Electron Molecular Ions Using Eckart Co-Ordinates

A new type of electronic Hamiltonian is constructed, using Eckart co-ordinates, by clamping the largest inertia momentum and the direction of the related inertia axis. Exact dissociation limits for the energies are obtained, and the use of electronic translation factors is avoided. Coupled equations for the nuclear motion are derived. They exhibit a special rotational coupling, whose constant is calculated for 1sσg - 2pσu states in the LCAO approximation.

Differential measurements of metastable Ne(2p53s3P0,2) on Ne(2p61S0) collisions at thermal energies

A time-of-flight technique is described which is used to measure elastic (direct and exchange) differential cross sections for collisions of Ne(2p53s 3P0,2) with Ne(2p6 1S0) at thermal energies in an experiment using two effusive beams. The angular dependence of the scattered intensity and the velocity dependence of the differential cross section in the backward scattering direction are given.