Biomedical subjects

G Roati

Publications and source records attributed to G Roati.

10 recordsLinked to original sources

PubMed2004

Radio frequency selective addressing of localized atoms in a periodic potential.

We study the localization and addressability of ultracold atoms in a combined parabolic and periodic potential. Such a potential supports the existence of localized stationary states and we show that applying a radio frequency field allows us to selectively address atoms in these states. This method is used to measure the energy and momentum distribution of the atoms in the localized states. We also discuss possible extensions of this scheme to address and manipulate atoms in single lattice sites.

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PubMed2004

Insulating behavior of a trapped ideal Fermi gas.

We investigate theoretically and experimentally the center-of-mass motion of an ideal Fermi gas in a combined periodic and harmonic potential. We find a crossover from a conducting to an insulating regime as the Fermi energy moves from the first Bloch band into the band gap of the lattice. The conducting regime is characterized by an oscillation of the cloud about the potential minimum, while in the insulating case the center of mass remains on one side of the potential.

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PubMed2004

Atom interferometry with trapped fermi gases.

We realize an interferometer with an atomic Fermi gas trapped in an optical lattice under the influence of gravity. The single-particle interference between the eigenstates of the lattice results in macroscopic Bloch oscillations of the sample. The absence of interactions between fermions allows a time-resolved study of many periods of the oscillations, leading to a sensitive determination of the acceleration of gravity. The experiment proves the superiority of noninteracting fermions with respect to bosons for precision interferometry and offers a way for the measurement of forces with microscopic spatial resolution.

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PubMed2004

Collisionally induced transport in periodic potentials.

We study the transport of ultracold atoms in a tight optical lattice. For identical fermions the system is insulating under an external force while for bosonic atoms it is conducting. This reflects the different collisional properties of the particles and reveals the role of interparticle collisions in establishing a macroscopic transport in a perfectly periodic potential. Also in the case of fermions we can induce a transport by creating a collisional regime through the addition of bosons. We investigate the transport as a function of the collisional rate and observe a transition from a regime in which the mobility increases with increasing collisional rate to one in which it decreases. We compare our data with a theoretical model for electron transport in solids introduced by Esaki and Tsu.

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PubMed2004

Expansion of a Fermi gas interacting with a Bose-Einstein condensate.

We study the expansion of an atomic Fermi gas interacting attractively with a Bose-Einstein condensate. We observe a slower evolution of the radial-to-axial aspect ratio which reveals the importance of the mutual attraction between the two samples during the first phase of the expansion. For large atom numbers, we also observe a bimodal momentum distribution of the Fermi gas, which reflects the spatial distribution of the mixture in trap. This effect allows us to extract important information on the overlap of the two species across the collapse.

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PubMed2003

Magnetic control of the interaction in ultracold K-Rb mixtures.

We predict the presence of several magnetic Feshbach resonances in selected Zeeman sublevels of the isotopic pairs 40K-87Rb and 41K-87Rb at magnetic fields up to 10(3) G. Positions and widths are determined combining a new measurement of the 40K-87Rb inelastic cross section with recent experimental results on both isotopes. The possibility of driving a K-Rb mixture from the weak to the strong interacting regime tuning the applied field should allow one to achieve the optimal conditions for boson-induced Cooper pairing in a multicomponent 40K-87Rb atomic gas and for the production of ultracold polar molecules.

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PubMed2002

Two atomic species superfluid.

We produce a quantum degenerate mixture composed by two Bose-Einstein condensates of different atomic species, 41K and 87Rb. We study the dynamics of the superfluid system in an elongated magnetic trap, where off-axis collisions between the two interacting condensates induce scissorlike oscillations.

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PubMed2002

Fermi-Bose quantum degenerate 40K-87Rb mixture with attractive interaction.

We report on the achievement of simultaneous quantum degeneracy in a mixed gas of fermionic 40K and bosonic 87Rb. Potassium is cooled to 0.3 times the Fermi temperature by means of an efficient thermalization with evaporatively cooled rubidium. Direct measurement of the collisional cross-section confirms a large interspecies attraction. This interaction is shown to affect the expansion of the Bose-Einstein condensate released from the magnetic trap, where it is immersed in the Fermi sea.

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PubMed2002

Collisional properties of ultracold K-Rb mixtures.

We determine the interspecies s-wave triplet scattering length a(3) for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between 41K and 87Rb in different temperature regimes. The positive value a(3)=+163(+57)(-12)a(0) ensures the stability against collapse of binary (41)K- (87)Rb Bose-Einstein condensates. For the fermion-boson mixture (40)K- (87)Rb, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

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PubMed2001

Bose-Einstein condensation of potassium atoms by sympathetic cooling.

We report on the Bose-Einstein condensation of potassium atoms, whereby quantum degeneracy is achieved by sympathetic cooling with evaporatively cooled rubidium. Because of the rapid thermalization of the two different atoms, the efficiency of the cooling process is high. The ability to achieve condensation by sympathetic cooling with a different species may provide a route to the production of degenerate systems with a larger choice of components.

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