Spin self-rephasing and very long coherence times in a trapped atomic ensemble.

We perform Ramsey spectroscopy on the ground state of ultracold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 ± 12 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems.

Beyond spontaneously broken symmetry in Bose-Einstein condensates.

Spontaneous symmetry breaking (SSB) for Bose-Einstein condensates cannot treat phase off-diagonal effects, and thus cannot explain Bell inequality violations. We describe another situation that is beyond a SSB treatment: an experiment where particles from two (possibly macroscopic) condensate sources are used for conjugate measurements of the relative phase and populations. Off-diagonal phase effects are characterized by a "quantum angle" and observed via "population oscillations," signaling quantum interference of macroscopically distinct states.

Fringe-free holographic measurements of large-amplitude vibrations.

In the measurement of the amplitude of vibration of objects, holographic imaging techniques usually involve fringe counting; because of the limited resolution of the images, measurements of large amplitudes are not accessible. We demonstrate a technique that suppresses the necessity of fringe counting--frequency sideband imaging--where the order of the sideband is considered a marker of the amplitude. The measurement is completely local: no comparison with another reference point on the object is necessary. It involves a sharp variation of a signal, which makes it robust against perturbations. The method is demonstrated in an experiment made with a vibrating clarinet reed; phase modulations as large as 1000 rad have been measured.

Cumulative identical spin rotation effects in collisionless trapped atomic gases.

We discuss the strong spin segregation in a dilute trapped Fermi gas recently observed by Du et al. with an "anomalous" large time scale and amplitude. In a collisionless regime, the atoms oscillate rapidly in the trap and average the inhomogeneous external field in an energy dependent way, which controls their transverse spin precession frequency. During interactions between atoms with different spin directions, the identical spin rotation effect transfers atoms to the up or down spin state, depending on their motional energy. Since low energy atoms are closer to the center of the trap than high energy atoms, the final outcome is a strong correlation between spins and positions.

Imaging a vibrating object by Sideband Digital Holography.

We obtain quantitative measurements of the oscillation amplitude of vibrating objects by using sideband digital holography. The frequency sidebands on the light scattered by the object, shifted by n times the vibration frequency, are selectively detected by heterodyne holography, and images of the object are calculated for different orders n. Orders up to n = 120 have been observed, allowing the measurement of amplitudes of oscillation that are significantly larger than the optical wavelength. Using the positions of the zeros of intensity for each value of n, we reconstruct the shape of vibration the object.

Nonlocal quantum effects with Bose-Einstein condensates.

We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins.

Long-lived quantum memory with nuclear atomic spins.

We propose to store nonclassical states of light into the macroscopic collective nuclear spin (10(18) atoms) of a 3He vapor, using metastability exchange collisions. These collisions, commonly used to transfer orientation from the metastable state 2 3S1 to the ground state of 3He, can also transfer quantum correlations. This gives a possible experimental scheme to map a squeezed vacuum field state onto a nuclear spin state with very long storage times (hours).

Internal state conversion in ultracold gases.

We consider an ultracold gas of (noncondensed) bosons or fermions with two internal states, and we study the effect of a gradient of the transition frequency between these states. When a pi/2 rf pulse is applied to the sample, exchange effects during collisions transfer the atoms into internal states which depend on the direction of their velocity. This results, after a short time, in a spatial separation between the two states. A kinetic equation is solved analytically and numerically; the results agree well with the recent observations of Lewandowski et al.

Nonanalytic dependence of the transition temperature of the homogeneous dilute Bose gas on scattering length.

We show that the shift in the transition temperature of the dilute homogeneous Bose gas is nonanalytic in the scattering amplitude a. The first correction beyond the positive linear shift in a is negative and of order a(2)lna. This nonuniversal nonanalytic structure indicates how the discrepancies between numerical calculations at finite a can be reconciled with calculations of the limit a-->0, since the linearity is apparent only for anomalously small a.

[Intestinal parasitic diseases and environment in Sahelo-Sudanese towns: the case of Pikine (Senegal)]. / Parasitoses intestinales et environnement dans les villes Sahélo-Soudaniennes: l'exemple de Pikine (Sénégal).

A survey carried out in Pikine (Senegal) on a sample of 5 groups of children drawn from ecologically representative sections of the town confirms the high prevalence in urban areas of Africa of intestinal infection, especially A. lumbricoides (35.6%), T. trichiura (35.4%), and Giardia (43.7%). The prevalence of A. lumbricoides (35.6%), T. trichiura (35.4%), and Giardia (43.7%). The prevalence of A. lumbricoides and T. trichiura are appreciably higher in the oldest sectors of the town or in those with a better sanitary standard: up to 47.7% for Ascaris and 46% for Trichuris. The use of X2 tests and log-linear analysis demonstrates a significant association between Ascaris and Trichuris. The highest prevalence for Giardia (56.8%) were to be found on the outskirts of the town, where the lowest prevalence of Ascaris (21.7%) and Trichuris (22.9%) were noted; moreover, age-based prevalence for the three parasites vary from one ecological area to another. The relationship between the urbanization process, the variation in environmental factors and intestinal parasitic infection, and the operational implications arising from this geographically-based approach are discussed.