Dynamical instability and dispersion management of an attractive condensate in an optical lattice

We investigate the stability of an attractive Bose-Einstein condensate in a moving 1D optical lattice in the presence of transverse confinement. By means of a Bogoliubov linear stability analysis we find that the system is dynamically unstable for low quasimomenta and becomes stable near the band edge, in a specular fashion with respect to the repulsive case. For low interactions the instability occurs via long wavelength excitations that are not sufficient for spoiling the condensate coherence, producing instead an oscillating density pattern both in real and momentum space. This behaviour is illustrated by simulations for the expansion of the condensate in a moving lattice.Comment: 5 pages, 4 figure

Beyond Perrault's experiments: repeatability, didactics and complexity

Abstract. The naturalistic and philosophical studies conducted in the second half of the 17th century were crucial both for the birth of modern hydrological science and modern epistemology. Thanks to quantitative observations and to the new experiment-based scientific approach, the Sun was about to be fully recognized as the engine of the hydrological cycle. In this context of great vitality and rapid cultural changes, Pierre Perrault published his classical opus De l'origine des fontaines (On the origin of springs) in 1674. The opus presents a discussion on the origin of springs and contains the report of a set of experiments of water flow through a soil column, which may be considered the first of modern hydrology. In assessing the importance of Perrault's opus, we will discuss his epistemological relevance by looking at the novelty of his approach, at the repeatability of the experiments, at the intriguing didactic aspects for the modern teaching of hydrology and at his attitude in facing the complexity of hydrological processes. Perrault places himself in the context of a novel experimental epistemology. On the basis of our analyses he seems to be aware that the processes involved in the hydrological cycle and in soil hydrology are hardly reproducible by means of a controlled laboratory model. This circumstance put the modern scientific approach to a severe test at its very beginning. It is suggested that some of Perrault's epistemological and methodological reflections are precursors of the modern epistemology of complexity. Thus even if Perrault's conclusions followed an ancient opinion, his work is not only seminal for hydrology, but also helps to enlighten some features of the scientific revolution of the 17th century

Association of ultracold double-species bosonic molecules

We report on the creation of heterospecies bosonic molecules, associated from an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated magnetic field close to two Feshbach resonances. We measure the binding energy of the weakly bound molecular states versus the Feshbach field and compare our results to theoretical predictions. We observe the broadening and asymmetry of the association spectrum due to thermal distribution of the atoms, and a frequency shift occurring when the binding energy depends nonlinearly on the Feshbach field. A simple model is developed to quantitatively describe the association process. Our work marks an important step forward in the experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure

Observing Coherence Effects in an Overdamped Quantum System

It is usually considered that the spectrum of an optical cavity coupled to an atomic medium does not exhibit a normal-mode splitting unless the system satisfies the strong coupling condition, meaning the Rabi frequency of the coherent coupling exceeds the decay rates of atom and cavity excitations. Here we show that this need not be the case, but depends on the way in which the coupled system is probed. Measurements of the reflection of a probe laser from the input mirror of an overdamped cavity reveal an avoided crossing in the spectrum which is not observed when driving the atoms directly and measuring the Purcell-enhanced cavity emission. We understand these observations by noting a formal correspondence with electromagnetically-induced transparency of a three-level atom in free space, where our cavity acts as the absorbing medium and the coupled atoms play the role of the control field

Double species condensate with tunable interspecies interactions

We produce Bose-Einstein condensates of two different species, $^{87}$Rb and $^{41}$K, in an optical dipole trap in proximity of interspecies Feshbach resonances. We discover and characterize two Feshbach resonances, located around 35 and 79 G, by observing the three-body losses and the elastic cross-section. The narrower resonance is exploited to create a double species condensate with tunable interactions. Our system opens the way to the exploration of double species Mott insulators and, more in general, of the quantum phase diagram of the two species Bose-Hubbard model.Comment: 4 pages, 4 figure

Collisional properties of sympathetically cooled 39^{39}K

We report the experimental evidence of the sympathetic cooling of $^{39}$K with $^{87}$Rb down to 1 $\mu$K, obtained in a novel tight confining magnetic trap. This allowed us to perform the first direct measurement of the elastic cross section of $^{39}$K below 50 $\mu$K. The result obtained for the triplet scattering length, $a_T = -51(7)$ Bohr radii, agrees with previous results derived from photoassociation spectra and from Feshbach spectroscopy of $^{40}$K.Comment: 7 pages, 4 figures, submitted to Phys. Rev.

Estimate of turbulent fluxes with eddy-covariance technique in a complex topography: A case study in the Italian Alps

A sensitivity analysis to different eddy—covariance data processing algorithms is presented for a dataset collected in an Alpine environment with complex topography. In Summer 2012 a micrometeorological station was installed at Cividate Camuno (274 m a.s.l., Oglio river basin, Central Italian Alps), in a flat and rectangular grass-covered lawn. The grass was 0.6 m tall during most of the field campaign. The station is equipped with traditional devices, four multiplexed TDR probes, and an eddy--covariance apparatus sampling at 20 Hz (Gill WindMaster Sonic Anemometer and Licor Li7500 Gas Analyzer), at about 3 m above the ground. The local winds regime is strongly affected by the morphology of the valley, and the topography is complex also due to the heterogeneity of the surrounding-areas land—cover. Using EddyPro software, the sensitivity of the turbulent fluxes estimate was assessed addressing three major issues of the data processing procedure, i.e. the choice of the computational averaging period, of the axis rotation method and of the data detrending criterion. Once identified three test periods of consecutive days without rainfall, the fluxes of momentum, sensible heat and latent heat were computed at the averaging period of 30, 60 and 120 min respectively. At each averaging period, both the triple rotation method, the double rotation method and the planar fit method were applied. Particularly the latter was applied both fitting a unique plane for all the wind directions and fitting multiple planes, one for each sector of the wind rose. Regarding the detrending criteria, data were processed with a block average and a linear detrend, the latter with time constant of 5, 30, 60 and 120 min respectively. Therefore, for each test period about 50 estimates of the fluxes were provided. As a result the obtained fluxes were compared. Even if with different flux quality, their pattern is quite stable with regard to the applied estimate procedures, but with sensitively different average values

Scanning electron microscopy of Rydberg-excited Bose-Einstein condensates

We report on the realization of high resolution electron microscopy of Rydberg-excited ultracold atomic samples. The implementation of an ultraviolet laser system allows us to excite the atom, with a single-photon transition, to Rydberg states. By using the electron microscopy technique during the Rydberg excitation of the atoms, we observe a giant enhancement in the production of ions. This is due to $l$-changing collisions, which broaden the Rydberg level and therefore increase the excitation rate of Rydberg atoms. Our results pave the way for the high resolution spatial detection of Rydberg atoms in an atomic sample

Observation of Stable Jones-Roberts Solitons in Bose-Einstein Condensates

We experimentally generate two-dimensional Jones-Roberts solitons in a three-dimensional atomic Bose-Einstein condensate by imprinting a triangular phase pattern. By monitoring their dynamics we observe that this kind of solitary waves are resistant to both dynamic (snaking) and thermodynamic instabilities, that usually are known to strongly limit the lifetime of dark plane solitons in dimensions higher than one. We additionally find signatures of a possible dipole-like interaction between them. Our results confirm that Jones-Roberts solitons are stable solutions of the non-linear Schr\"odinger equation in higher dimensions and promote these excitations for applications beyond matter wave physics, like energy and information transport in noisy and inhomogeneous environments

Observation of heteronuclear atomic Efimov resonances

The Efimov effect represents a cornerstone in few-body physics. Building on the recent experimental observation with ultracold atoms, we report the first experimental signature of Efimov physics in a heteronuclear system. A mixture of $^{41}$K and $^{87}$Rb atoms was cooled to few hundred nanoKelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative. We attribute the two features at negative scattering length to the existence of two kind of Efimov trimers, namely KKRb and KRbRb.Comment: 4 pages, 4 figure