39-K Bose-Einstein condensate with tunable interactions

We produce a Bose-Einstein condensate of 39-K atoms. Condensation of this species with naturally small and negative scattering length is achieved by a combination of sympathetic cooling with 87-Rb and direct evaporation, exploiting the magnetic tuning of both inter- and intra-species interactions at Feshbach resonances. We explore tunability of the self-interactions by studying the expansion and the stability of the condensate. We find that a 39-K condensate is interesting for future experiments requiring a weakly interacting Bose gas.Comment: 5 page

Misure gravimetriche a L’Aquila. Confronto con i valori rilevati nel 1995

Nel febbraio 2010 si è dato inizio alla realizzazione di una rete gravimetrica a L’Aquila con l’istituzione di una stazione assoluta. La stazione è stata realizzata nel Palazzo Comunale della città di L’Aquila (Palazzo Margherita – foto a), nel centro della città, in un locale al piano terra (foto b). Sono state effettuata anche misure gravimetriche relative al fine di misurare il locale gradiente verticale della gravità (foto c) e riportare il valore assoluto ad una stazione satellite esterna all’edificio (foto d). Nel corso della campagna è stato anche effettuato il collegamento gravimetrico tra la nuova stazione e quella istituita nel 1995 nei laboratori sotterranei dei Laboratori Nazionali del Gran Sasso (LNGS) (foto e) dove è stato anche misurato il gradiente verticale. Tale punto fu allora istituito quale nodo fondamentale della costituenda “Rete Gravimetrica Nazionale di Ordine Zero”

Thirty years of precise gravity measurements at Mt. Vesuvius: an approach to detect underground mass movements

Since 1982, high precision gravity measurements have been routinely carried out on Mt. Vesuvius. The gravity network consists of selected sites most of them coinciding with, or very close to, leveling benchmarks to remove the effect of the elevation changes from gravity variations. The reference station is located in Napoli, outside the volcanic area. Since 1986, absolute gravity measurements have been periodically made on a station on Mt. Vesuvius, close to a permanent gravity station established in 1987, and at the reference in Napoli. The results of the gravity measurements since 1982 are presented and discussed. Moderate gravity changes on short-time were generally observed. On long-term significant gravity changes occurred and the overall fields displayed well defined patterns. Several periods of evolution may be recognized. Gravity changes revealed by the relative surveys have been confirmed by repeated absolute measurements, which also confirmed the long-term stability of the reference site. The gravity changes over the recognized periods appear correlated with the seismic crises and with changes of the tidal parameters obtained by continuous measurements. The absence of significant ground deformation implies masses redistribution, essentially density changes without significant volume changes, such as fluids migration at the depth of the seismic foci, i.e. at a few kilometers. The fluid migration may occur through pre-existing geological structures, as also suggested by hydrological studies, and/or through new fractures generated by seismic activity. This interpretation is supported by the analyses of the spatial gravity changes overlapping the most significant and recent seismic crises

Toward Absolute Gravity Networks to Monitor the Neapolitan Volcanoes

As well known, measurements of the time-space changes of the gravity field are a powerful approach to detect the masses change/redistribution in the underground, such as those at volcanoes. The most common approach to detect gravity precursory signals is the use of repeated relative measurements at benchmarks on networks. This is very good, but has some and significant limits: 1) the networks must be linked to a reference station stable over long time and if possible external to the active area. This is quite simply for land volcanoes, but is generally difficult for volcanoes on islands, particularly when far from the terra firma; 2) to reach high precision, measurements require special operative procedure implying long time surveys; 3) relative gravity changes can be affected over the long-time by changes of instrumental sensitivity and loss of vacuum in the air-tight sealing system, therefore the instruments must be subject to continuous check. Measurements on network have the advantage to permit to define the position and the geometry of the masses change/redistribution, even if they suffer from the lack of information about the rate and/or quick changes, since variations are assumed linearly changing over the time between two consecutive surveys, usually spaced out some months or years. This is a fundamental information in the prediction of the volcanic activity changes and/or of volcanic eruptions and leads to conclude that measurements on networks cannot be excluded from a monitoring program, but moving toward absolute methodologies is advisable. Nowadays, and since some years, this is possible due to the commercially availability of a portable field absolute gravimeter (Micro-g_LaCoste A10), which we acquired at the end of 2014. The main advantages of the absolute measurements on networks are: i) they are independent from any reference and the field operation are faster and easier, permitting much frequent measurements and reducing the lack of information between two consecutive surveys; ii) they are directly linked to standards of time and length therefore fairly independent from instrumental references and drift, avoiding loss of long-term information; iii) the measured value can be used without loop reductions, post processing and benchmark links. This can be translated into large advantages, such as saving of human resources, survey’s time and costs. Before to start field surveys, we carried out several measurements to test the performances of the instrument and mainly to verify the repeatability of the measured value. The test was performed at the Old Building of the Osservatorio Vesuviano, on Mount Vesuvio, that is a very low noised and good logistic site; it is one of the absolute stations installed in 80’s in the Neapolitan area which value has been measured several time till 2010. In June 2015, starting from Campi Flegrei, we set the first absolute gravity networks on the Neapolitan volcanoes, formed by stations coinciding or close to the benchmarks of the already existing relative networks. Here we present and discuss the data collected during the test and the field surveys; we also will describe the new absolute networks

MISURE GRAVIMETRICHE ALL’ISOLA DI PANTELLERIA

Nel mese di giugno 2009 è stata condotta una campagna gravimetrica di precisione all’isola di Pantelleria, dove le misure vengono effettuate con una periodicità biennale data la debole attività dell’isola. Le misure sono state rilevate sull’intera rete che è costituita da 24 stazioni (figura 1), molte delle quali ubicate su vertici della locale linea di livellazione e tutte collegate a due stazioni assolute istituite nel 1993 rispettivamente a Pantelleria e a Khamm

Feshbach resonances in ultracold K(39)

We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by studying atom losses and molecule formation. Accurate determination of the magnetic-field resonance locations allows us to optimize a quantum collision model for potassium isotopes. We employ the model to predict the magnetic-field dependence of scattering lengths and of near-threshold molecular levels. Our findings will be useful to plan future experiments on ultracold potassium atoms and molecules.Comment: 7 pages, 6 figure

Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture

The route toward a Bose-Einstein condensate of dipolar molecules requires the ability to efficiently associate dimers of different chemical species and transfer them to the stable rovibrational ground state. Here, we report on recent spectroscopic measurements of two weakly bound molecular levels and newly observed narrow d-wave Feshbach resonances. The data are used to improve the collisional model for the Bose-Bose mixture 41K87Rb, among the most promising candidates to create a molecular dipolar BEC.Comment: 13 pages, 3 figure