G. Dutier

Exploring the van der Waals atom-surface attraction in the nanometric range

The van der Waals atom-surface attraction, scaling as C3z?3 for z the atom-surface distance, is expected to be valid in the distance range 1?1000?nm, covering 8?10 orders of magnitudes in the interaction energy. A Cs vapour nanocell allows us to analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2 ? 6D5/2 transition. The measured C3 value is found to be independent of the thickness in the explored range 40?130?nm, and is in agreement with an elementary theoretical prediction. We also discuss the specific interest of exploring short distances and large interaction energy.

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.

Study of low-energy resonant metastability exchange in argon by a pulsed merging beam technique

The resonant metastability exchange process in low-energy collinear collisions between metastable argon atoms (Ar* 3P2) polarized in spin (M = +2) and ground-state Ar atoms from a nozzle beam is studied by means of a time-of-flight technique. A wide range of metastable atom velocities in the laboratory frame (275 m s−1 down to 50 m s−1) is obtained by use of a Zeeman slower, the counter-propagating laser beam of which is locked in frequency onto the 3P2–3D3 closed transition (λ = 811.5 nm). The accessible centre-of-mass energy range (8–27 meV) has not been explored so far, to our knowledge. Calculations based upon existing interatomic potentials of 2g and 2u symmetries are in reasonable agreement with experiment.

Probing an atomic gas confined in a nanocell

Since the recent realization of extremely thin vapour cells (local thickness: 20-1000 nm), we investigate the optical properties of these 1-D confined vapours. Aside from their interest for Doppler-free spectroscopy, nanocells offer a new tool to evaluate collisional shift and broadening, yielding an access to the open problem of collisions under confinement. It also allows probing of the atom-surface interaction in a range of unusual short distances. The experimental exploration of the distance dependence, normally evolving according to the z -3 van der Waals (vW) dependence (z : the atom-surface distance), is worth doing because it could be affected by imperfections of the real surface, such as roughness, adsorbed impurities or charges. A detailed lineshape analysis is now under progress, with tight constraints imposed to the fitting by the twin information brought by simultaneous reflection and transmission spectra. Another issue is a possible resonant enhancement, susceptible to induce a repulsive vW, due to the coupling between atom excitation and a surface mode.

Atom-surface interaction at the nanometre scale: van der Waals-Zeeman transitions in a magnetic field

van der Waals-Zeeman transitions between magnetic states of metastable rare-gas atoms Ar*, Kr* and Xe* (3P2) induced by a solid surface in the presence of a magnetic field, are investigated theoretically and experimentally. By use of a Zeeman slower, metastable argon atoms with various velocities ranging from 170 to 560 m/s allow us to investigate the small impact parameter range (3–7 nm) within which these transitions occur, as well as the effect of atom polarisation on the sharing out of the M states.

Nanoscopy of Surface-Induced van der Waals-Zeeman Transitions

van der Waals transitions among magnetic sub‐levels of a metastable rare gas atom passing near a surface immersed in a magnetic field, are described. Related transition amplitudes are calculated using both the sudden and the Landau‐Zener approximations. Experimental data for Ne*(3P2) atoms traversing a copper grating are presented. For a pair of surfaces (e.g. the opposite edges of a slit) and a sufficiently large coherence width, Fresnel’s biprism interference fringes are obtained. From this interference pattern, detailed information about the transition amplitude at a sub‐nanometric scale can be derived. The effect of gravity on this pattern is examined.

A simple velocity-tunable pulsed atomic source of slow metastable argon

A pulsed beam of metastable argon atoms having a low tunable velocity (10 to 150 m s−1) is produced with a very substantial brightness (9 × 108Ar* s−1 sr−1). The present original experimental configuration leads to a variable velocity dispersion that can be smaller than the standard Brownian one. This behaviour, analysed using Monte Carlo simulations, exhibits momentum stretching (heating) or narrowing (cooling) entirely due to a subtle combination of Doppler and Zeeman effects.

Van der Waals - Zeeman transitions of slow metastable argon atoms Ar*( 3 P 2 )

Metastable argon atoms Ar*(3P2), produced by electron bombardment of a nozzle beam of ground state Ar atoms, are slowed down from their initial thermal velocity of 560 m/s down to a few tens of m/s, using a standard Zeeman slower. In this decelerator [1], a repulsive force is induced by a counter-propagating σ+-polarized laser beam, locked in frequency on the 3P2-3D3 closed transition (λ = 811.5 nm) and then detuned by 340 MHz. A special profile of longitudinal magnetic field is adjusted in order to maintain atoms in resonance with light all over the device, by compensating the variable Doppler shift by the convenient Zeeman shift. Low velocities, e.g. 55 m/s, are accessible but due to spontaneous emission randomly distributed recoil momentums enlarge both angular and velocity distributions of the beam [2]. Nevertheless, by placing off axis collimating slits and grating, it is in principle possible to observe transmission and/or diffraction phenomena specific of low velocities.

“Meta-optics” for Matter Waves

With the fast development of matter-wave optics, many of the functions previously operated in light optics have been realised: atom diffraction, mirrors, beam splitters, atom holography, quantum reflection, etc. Similarities and differences originate in the properties of the associated particle: non-zero atom mass, vacuum dispersion for the “de Broglie” waves, influence of the internal atomic degrees of freedom… Along this viewpoint, novel areas in the field of atom optics are presently explored. For instance, it includes the devising of non-diffracting atom nano-beams thanks to a specially designed transverse Stern-Gerlach interferometer [1]. The non-diffracting character is linked to the special shape of the resulting transverse profile which is of the Lorentz type, recalling Bessel beams in light optics [2].

Entanglement of molecular-orientation, rotational and orbital degrees of freedom in multiphoton orientational wave packets

Multiphoton orientational wave packets induced by short resonant polarized laser pulses in a rotationally-frozen interacting molecule contain relevant information. The entanglement of the orbital, rotational and orientational degrees of freedom shows a strong dependence on the polarization state of the absorbed photons and the space orientation of the interacting molecule and enables one to assign the orbital state of the excited molecular electron, to measure the space orientation of the interacting molecule from the orientational recurrences, to relate the measured temporal widths to the angular momentum photon state and the coherence of the laser pulse, to obtain information on the ground rotational state, or to measure the effective temperature of an isotropic molecular assembly. The space orientation of a small number of independent molecules can be distinguished from their distinct orientational dependence in the formation of the individual orientational wave packets.