161 research outputs found
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 nanoparticles'shape 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.Comment: 14 pages,6 figures, http://iopscience.iop.org/1612-202X/11/8/085902
-enhanced grey molasses on the transition of Rubidium-87 atoms
Laser cooling based on dark states, i.e. states decoupled from light, has
proven to be effective to increase the phase-space density of cold trapped
atoms. Dark-states cooling requires open atomic transitions, in contrast to the
ordinary laser cooling used for example in magneto-optical traps (MOTs), which
operate on closed atomic transitions. For alkali atoms, dark-states cooling is
therefore commonly operated on the transition . We show that, for , thanks to the large hyperfine
structure separations the use of this transition is not strictly necessary and
that quasi-dark state cooling is efficient also on the line, . We report temperatures as low as K and an increase of almost an order of magnitude in the phase space
density with respect to ordinary laser sub-Doppler cooling
Efficient all-optical production of large Li quantum gases using D gray-molasses cooling
We use a gray molasses operating on the D atomic transition to produce
degenerate quantum gases of Li with a large number of atoms. This
sub-Doppler cooling phase allows us to lower the initial temperature of 10
atoms from 500 to 40 K in 2 ms. We observe that D cooling remains
effective into a high-intensity infrared dipole trap where two-state mixtures
are evaporated to reach the degenerate regime. We produce molecular
Bose-Einstein condensates of up to 510 molecules and
weakly-interacting degenerate Fermi gases of 10 atoms at
with a typical experimental duty cycle of 11 seconds.Comment: 5 pages, 3 figure
Exploring the ferromagnetic behaviour of a repulsive Fermi gas via spin dynamics
Ferromagnetism is a manifestation of strong repulsive interactions between
itinerant fermions in condensed matter. Whether short-ranged repulsion alone is
sufficient to stabilize ferromagnetic correlations in the absence of other
effects, like peculiar band dispersions or orbital couplings, is however
unclear. Here, we investigate ferromagnetism in the minimal framework of an
ultracold Fermi gas with short-range repulsive interactions tuned via a
Feshbach resonance. While fermion pairing characterises the ground state, our
experiments provide signatures suggestive of a metastable Stoner-like
ferromagnetic phase supported by strong repulsion in excited scattering states.
We probe the collective spin response of a two-spin mixture engineered in a
magnetic domain-wall-like configuration, and reveal a substantial increase of
spin susceptibility while approaching a critical repulsion strength. Beyond
this value, we observe the emergence of a time-window of domain immiscibility,
indicating the metastability of the initial ferromagnetic state. Our findings
establish an important connection between dynamical and equilibrium properties
of strongly-correlated Fermi gases, pointing to the existence of a
ferromagnetic instability.Comment: 8 + 17 pages, 4 + 8 figures, 44 + 19 reference
Studio e realizzazione di un sistema sperimentale per ingranaggi a vite senza fine e ruota elicoidale
Si tratta di un lavoro di ripristino e validazione di un banco prova per vite senza fine e ruota elicoidale. Il cuore del lavoro è la ricostruzione della geometria tridimensionale dei campioni e della scatola di prova, effettuata col software catia v
Connecting dissipation and phase slips in a Josephson junction between fermionic superfluids
We study the emergence of dissipation in an atomic Josephson junction between
weakly-coupled superfluid Fermi gases. We find that vortex-induced phase
slippage is the dominant microscopic source of dissipation across the BEC-BCS
crossover. We explore different dynamical regimes by tuning the bias chemical
potential between the two superfluid reservoirs. For small excitations, we
observe dissipation and phase coherence to coexist, with a resistive current
followed by well-defined Josephson oscillations. We link the junction transport
properties to the phase-slippage mechanism, finding that vortex nucleation is
primarily responsible for the observed trends of conductance and critical
current. For large excitations, we observe the irreversible loss of coherence
between the two superfluids, and transport cannot be described only within an
uncorrelated phase-slip picture. Our findings open new directions for
investigating the interplay between dissipative and superfluid transport in
strongly correlated Fermi systems, and general concepts in out-of-equlibrium
quantum systems.Comment: 6 pages, 4 figures + Supplemental Materia
Dinamiche insediative e aspetti culturali dell’Ager Volaterranus tra Orientalizzante e etá arcaica: nuovi contributi dalla cittá e dalla Val di Cecina
Studio delle dinamiche insediative a Volterra tra l’età orientalizzante e l’età arcaica nel territorio volterrano a partire dall’analisi dei dati offerti dagli scavi degli insediamenti di Casalvecchio (Casale Marittimo) e Casalgiustri (Montescudaio) e da contesti di ambito urbano a confronto con la distribuzione e gli aspetti culturali delle sepolture della Valdicecin
Effect of interactions in the interference pattern of Bose-Einstein condensates
Understanding the effect of interactions in the phase evolution of expanding atomic Bose-Einstein condensates is fundamental to describing the basic phenomenon of matter wave interference. Many theoretical and experimental works tackled this problem, always with the implicit assumption that the mutual interaction between two expanding condensates rigidly modifies the phase evolution through an effective force. In this paper, we present a combined experimental and theoretical investigation of the interference profile of expanding Rb-87 condensates, with a specific focus on the effect of interactions. We come to the different conclusion that the mutual interaction produces local modifications of the condensate phase only in the region where the wave packets overlap.We acknowledge fruitful discussions with M. Fattori, L. Masi, M. Prevedelli, R. Corgier, and A. Smerzi and we thank M. Inguscio for continuous support. This work was supported by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund FEDER through Grant No. PGC2018-101355-B-I00 (MCIU/AEI/FEDER, UE), by the Basque Government through Grant No. IT986-16, by the European Commission through FET Flagship on Quantum Technologies-Qombs Project (Grant No. 820419), and by Fondazione Cassa di Risparmio Firenze through project "SUPERACI-Superfluid Atomic Circuits.
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