F. Perales

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.

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.

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.

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 560u2009m/s allow us to investigate the small impact parameter range (3–7u2009nm) 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.

Coherent Atom Optics with fast metastable rare gas atoms

Coherent atom optics experiments making use of an ultra‐narrow beam of fast metastable atoms generated by metastability exchange are reported. The transverse coherence of the beam (coherence radius of 1.7 μm for He*, 1.2 μm for Ne*, 0.87 μm for Ar*) is demonstrated via the atomic diffraction by a non‐magnetic 2μm‐period reflection grating. The combination of the non‐scalar van der Waals (vdW) interaction with the Zeeman interaction generated by a static magnetic field gives rise to “vdW‐Zeeman” transitions among Zeeman sub‐levels. Exo‐energetic transitions of this type are observed with Ne*(3P2) atoms traversing a copper micro‐slit grating. They can be used as a tunable beam splitter in an inelastic Fresnel bi‐prism atom interferometer.

Qualitative analysis of the right - left scattering asymmetry in low-energy collisions

The experimental results on the right - left scattering asymmetry of helicopter-polarized atoms, either in state or colliding with Ar, are presented and qualitatively interpreted in the framework of the sudden-locking model. It is shown that this model provides a simple description of key features of the cross section difference and the relation between it and the total cross section for scattering of unpolarized atoms.

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.

Dynamics of evanescent matter waves in negative-index media

Semi-evanescent and evanescent matter waves produced by an atom wave packet impinging on a repulsive barrier can be back-refracted and reconstructed by the application of negative-index comoving potential pulses. One shows that those collapses and revivals generate a matter wave confined on both sides of the barrier border (surface matter wave) and should be observable via the retardation of atom reflection from the barrier interface. This property, joined to the possibility recently demonstrated of inducing negative refraction of atom waves, makes such potentials a matter-wave counterpart of negative-index materials or meta materials well known in light optics.