Alessia Burchianti

Full control of sodium vapor density in siloxane-coated cells using blue LED light-induced atomic desorption

We propose and experimentally implement a method, based on light-induced atomic desorption, for controlled generation of large sodium densities in siloxane-coated cells, kept at room temperature. An array of blue LEDs is used to desorb sodium atoms from the cell walls. The required atomic vapor density is achieved and stabilized by controlling the LED power through the feedback given by the sodium fluorescence. We show that sodium densities corresponding to about 400 K can be obtained and kept stable for a long time with less than 6 mW of LED light power. Moreover, this technique allows for precise vapor density modulation with a frequency of tenths of hertz, which is not possible using traditional heating methods.

Optical recording in Rb loaded-porous glass by reversible photoinduced phase transformations

We report reversible phase transformations in Rb loaded-porous glass irradiated with weak laser light which allow us to realize image storage on it. The effect is due to photo-induced changes of Rb distribution inside the glass pores, where atomic photodetachment and confinement produce either formation or evaporation of Rb nanoclusters. These processes depend on light frequency and intensity making controllable by light the porous glass transparency. We demonstrate that porous glass doped with Rb can be used as a support to record a light pulse for a long time as well as to remember the order of light colors in an illumination sequence.

Repulsive Fermi Polarons in a Resonant Mixture of Ultracold Li 6 Atoms

We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

Light-induced atomic desorption and related phenomena

We review some recent studies on light-induced atomic desorption (LIAD) from dielectric surfaces. Alkali-metal atoms adsorbed either on organic films or on porous glass are released into the vapor phase under illumination. The measurements were performed in Pyrex resonance cells either coated with siloxane films or containing a porous glass sample. In both cases, the experimental results show that LIAD can be used to produce atomic densities suitable for most atomic physics experiments. Moreover, we find that photoinduced effects, correlated with LIAD, produce reversible formation and evaporation of alkali-metal clusters in porous glass. These processes depend on the light frequency, making the porous glass transmittance controllable by light.

All-optical vapor density control for electromagnetically induced transparency

We demonstrate the feasibility of coherent spectroscopy experiments in alkali vapors at room temperature by using an automatic all-optical atomic dispenser. The reliability of the system is proved by observing electromagnetically induced transparency (EIT) resonances in siloxane-coated cells where large and stable K densities are achieved by light-controlled atomic desorption from the cell coating. The experimental results prove that this technique preserves the orientation of the atomic system, and, at the same time, allows a fine, continuous, and rapid control of the vapor density also suitable for magnetic-sensitive applications.

The Legnaro francium magneto-optical trap

Laser cooling and trapping of radioactive atoms represent the new frontier in atomic physics and a new powerful tool in nuclear physics. We are setting up at the INFN-Legnaro National Laboratories a laser cooling facility that has as a first goal the realization of a 210Fr magneto-optical trap. The general outline of the experiment and the improvements of the final trap efficiency are discussed. Some preliminary results are presented.

Josephson plasma oscillations and the Gross-Pitaevskii equation: Bogoliubov approach versus two-mode model

We show that the Josephson plasma frequency for a condensate in a double-well potential, whose dynamics is described by the Gross-Pitaevskii (GP) equation, can be obtained with great precision by means of the usual Bogoliubov approach, whereas the two-mode model - commonly constructed by means of a linear combinations of the low-lying states of the GP equation - generally provides accurate results only for weak interactions. A proper two-mode model in terms of the Bogoliubov functions is also discussed, revealing that in general a two-mode approach is formally justified only for not too large interactions, even in the limit of very small amplitude oscillations. Here we consider specifically the case of a one-dimensional system, but the results are expected to be valid in arbitrary dimensions.

Optical stabilization of Rb vapor density above thermal equilibrium

We stabilize the Rb vapor density above its thermal equilibrium value in sealed glass cells, which are generally used in atomic physics experiments. The method relies on light-induced desorption of Rb atoms from dielectric surfaces. The process does not demand high light intensities so that LEDs or laser diodes can be used as desorbing sources. The experiments are carried out in Pyrex cells either coated with a polydimethylsiloxane film or containing a porous glass sample. Under illumination both the organic coating and the porous sample release a large amount of Rb atoms into the cell volume. We show that the Rb vapor density can be maintained to a preset value, using a desorbing light intensity controlled by a feedback signal given by the Rb absorption or fluorescence level. Moreover, we find that the stabilization technique does not depend on the microscopic mechanisms underlying photodesorption.

Cooling and trapping of radioactive atoms: the Legnaro francium magneto-optical trap

A magneto-optical trap for francium radioactive atoms has been set up at the Istituto Nazionale di Fisica Nucleare, Legnaro laboratories, and its characterization and optimization are under way. The main features of the Fr+ beam line, of the target, and of the magneto-optical trap are described in detail. Measurements of the Fr-ion production rate as a function of the target temperature, the primary beam intensity, and energy have been made. Preliminary tests with other stable alkali atoms aimed at an improvement of the magneto-optical trap collection efficiency are reported. Fast and efficient trap loading of rubidium has been obtained through the light-induced atomic desorption from an organic coating. A larger number of sodium atoms, as compared with a monochromatic trapping laser, has been trapped by use of a broadband laser.

Laser-driven self-assembly of shape-controlled potassium nanoparticles in porous glass

We observe growth of shape-controlled potassium nanoparticles inside a random network of glass nanopores, exposed to low-power laser radiation. Visible laser light plays a dual role: it increases the desorption probability of potassium atoms from the inner glass walls and induces the self-assembly of metastable metallic nanoparticles along the nanopores. By probing the sample transparency and the atomic light-induced desorption flux into the vapour phase, the dynamics of both cluster formation/evaporation and atomic photo-desorption processes are characterized. Results indicate that laser light not only increases the number of nanoparticles embedded in the glass matrix but also influences their structural properties. By properly choosing the laser frequency and the illumination time, we demonstrate that it is possible to tailor the nanoparticlesshape distribution. Furthermore, a deep connection between the macroscopic behaviour of atomic desorption and light-assisted cluster formation is observed. Our results suggest new perspectives for the study of atom/surface interaction as well as an effective tool for the light-controlled reversible growth of nanostructures.