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At the interface between two fluid layers in relative motion, infinitesimal fluctuations can be exponentially amplified, inducing vorticity and the breakdown of the laminar flow. This process, known as the Kelvin-Helmholtz instability, is responsible for many familiar phenomena observed in the atmosphere, and the oceans, as well as in astrophysics, and it is one of the paradigmatic routes to turbulence in fluid mechanics. While in classical hydrodynamics the instability is ruled by universal scaling laws, to what extent universality emerges in quantum fluids is yet to be fully understood. Here, we shed light on this matter by triggering the Kelvin-Helmholtz instability in atomic superfluids across widely different regimes, ranging from weakly-interacting bosonic to strongly-correlated fermionic pair condensates. Upon engineering two counter-rotating flows with tunable relative velocity, we observe how their contact interface develops into an ordered circular array of quantized vortices, which loses stability and rolls up into clusters in close analogy with classical Kelvin-Helmholtz dynamics. We extract the instability growth rates by tracking the position of individual vortices and find that they follow universal scaling relations, predicted by both classical hydrodynamics and a microscopic point-vortex model. Our results connect quantum and classical fluids revealing how the motion of quantized vortices mirrors the interface dynamics and open the way for exploring a wealth of out-of-equilibrium phenomena, from vortex-matter phase transitions to the spontaneous emergence of two-dimensional quantum turbulence .

We report on the production of a K41-Rb87 dual-species Bose-Einstein condensate in a hybrid trap, consisting of a magnetic quadrupole and an optical dipole potential. After loading both atomic species in the trap, we cool down Rb87 first by magnetic and then by optical evaporation, while K41 is sympathetically cooled by elastic collisions with Rb87. We eventually produce two-component condensates with more than 105 atoms and tunable species population imbalance. We observe the immiscibility of the quantum mixture by measuring the density profile of each species after releasing them from the trap.

We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold Li-6 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 Gamma. 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.

International audience; We report on the production of a K-41-Rb-87 dual-species Bose-Einstein condensate in a hybrid trap, consisting of a magnetic quadrupole and an optical dipole potential. After loading both atomic species in the trap, we cool down Rb-87 first by magnetic and then by optical evaporation, while K-41 is sympathetically cooled by elastic collisions with Rb-87. We eventually produce two-component condensates with more than 10(5) atoms and tunable species population imbalance. We observe the immiscibility of the quantum mixture by measuring the density profile of each species after releasing them from the trap.

Entanglement is a fundamental resource for quantum information processing [1-3], its applications including scalable quantum communication, secure quantum key distribution protocols for cryptography, and exponential speedup of quantum algorithms. It occurs naturally in manybody systems at low temperatures: This makes cold atoms good candidates to provide entangled states involving a large number of particles. For realizing and manipulating such states, an essential task is quantifying the actual amount of entanglement contained in the created state before using it for quantum information protocols. However, this task represents a major challenge, as it requires either full state tomography, scaling exponentially in the system size, or the assumption of unverified system characteristics such as its Hamiltonian or temperature. In this experiment [4], we obtain a quantification of multipartite entanglement from readily accessible measurements - that is, time-of-flight atomic density distribution - based on a recent proposal [5]. We directly observe and quantify the multipartite spatial entanglement between the sites of a periodic optical potential (optical lattice) that hosts massive bosonic particles. We characterize its behaviour when crossing the superfluid-Mott insulator transition and when varying temperature, demonstrating the robustness of our method. References [1] M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, Cambridge University Press (Cambridge, 2000). [2]R. Horodecki, P. Horodecki, M. Horodecki, and K. Horodecki, Quantum entanglement, Rev. Mod. Phys. 81, 865-942 (2009). [3]O. Göhne and G. Tóth, Entanglement detection, Physics Reports 474, 1-75 (2009). [4]M. Cramer, A. Bernard, N. Fabbri, L. Fallani, C. Fort, S. Rosi, F. Caruso, M. Inguscio, and M. B. Plenio, Entanglement of bosons in optical lattices, E-print arXiv:1302.4897 [5]M. Cramer, M. B. Plenio, and H. Wunderlich, Measuring entanglement in condensed matter systems, Phys. Rev. Lett. 106, 020401 (2011).

Inhibition of the Na+/K(+)-ATPase by a circulating endogenous digitalis- or ouabain-like substance has been associated with the pathogenesis of several forms of clinical and experimental hypertension. Inbred salt-sensitive Dahl SS/jr rats were immunized with either urease or a ouabain-urease conjugate, then challenged with a high salt diet. The salt-induced increase in blood pressure in the ouabain-urease-immunized animals was significantly less than that of the urease-inoculated rats. Sera of the ouabain-urease immunized animals cross-reacted with ouabagenin, digoxigenin, digoxin, and digitoxin, but not with aldosterone, corticosterone, deoxycorticosterone (DOC), 18-hydroxy DOC, or 19-nor DOC. The fact that hypertension was not completely blocked by immunization supports ample evidence that the disease in these animals is multifactorial with several genes involved.

This paper has been withdrawn by the authors. The authors have now written two separate papers, one theoretical (A. Smerzi, A. Trombettoni, P. G. Kevrekidis, and A. R. Bishop Phys. Rev. Lett. 89, 170402 (2002)) and one experimental (F. S. Cataliotti, L. Fallani, F. Ferlaino, C. Fort, P. Maddaloni, and M. Inguscio New Journal of Physics 5, 71 (2003)).

El presente trabajo trata el tema de la corrupción y falta de transparencia en las adquisiciones del sector público y los instrumentos que pueden colaborar para obtener resultados positivos en la gestión de compras. En primer lugar, se plantea el estado actual de la discusión del tema y la preocupación que manifiestan los gobiernos, los organismos internacionales, los centros académicos, las organizaciones no gubernamentales y la sociedad civil ante el avance de la corrupción. Se destaca la importancia del tema en Argentina y en otros países latinoamericanos, sobre todo su impacto en el crecimiento económico y las ineficiencias e inequidades que crea en la economía. En segundo término, se analiza la base de datos generada por la Subsecretaría de Gerenciamiento Estratégico del Gobierno Autónomo de la Ciudad de Buenos Aires. El objetivo central es evaluar el impacto de la Reforma Administrativa (1998) en los precios de 24 productos adquiridos por 13 hospitales generales de agudos durante el período 1998-1999. Se analizan los precios ponderados, las cantidades adquiridas y los montos de las contrataciones para el citado período y el conjunto de productos de mayor tasa de utilización. Se utilizó el análisis factorial multivariante a fin de identificar aquellos establecimientos asistenciales que tuvieron un buen nivel de actividad y a la vez un buen manejo presupuestario (indicadores de actividad y gestión). El análisis del comportamiento de los precios se realiza a través de una serie de regresiones que permiten demostrar que los precios bajaron un 8% en 1999. La contribución de cada hospital a esta variación se modela con variables dicotómicas. Así, 6 de los 13 hospitales aportan significativamente a la reducción de precios, de los cuales 3 contribuyen además a la baja en la dispersión de precios. Los resultados obtenidos permiten concluir que si los establecimientos asistenciales públicos cuentan con instrumentos de gestión de compra claros y precisos y con una normativa homogénea y uniforme, pueden lograr un buen nivel de actividad. Además, pueden contribuir a la baja de precios y la disminución de la dispersión de los mismos, a la vez que mejoran la eficiencia en la asignación y utilización de los recursos. This paper deals with corruption and the lack of transparency in public sector purchases as well as with the main instruments to obtain adequate results in purchase negotiation. Firstly, we discuss how corruption causes concern to national governments, international organizations, academic centers, non-governmental organizations and society in general. The consequences of corruption in Argentina and other Latin American countries are highlighted, especially the effect of corruption on economic growth and the way it creates economic inefficiency and inequality. Secondly, the database created by the Subsecretary of Strategic Management of the Autonomous Government of the City of Buenos Aires is analyzed. The central purpose of this study is to evaluate the impact of the Administrative Reform of 1998 on the prices of 24 products acquired by 13 general acute care hospitals from 1998-1999. The weighted prices, the number of units purchased and the total number of contracts given in this period, as well as the products with the greatest utilization rate, are analyzed. Multivariante analysis was used to identify hospitals with appropriate activity and efficient budeget administration (activity and negotiation indicators). Price development was analyzed using the regression technique (ordinary least squares), which demonstrated an 8% reduction in prices for the year 1999. The contribution of each hospital to this variation is presented using dummy variables. Thus, six of the 13 hospitals significantly contributed to the decrease in prices. Of these six, three hospitals also contributed to reduction in price dispersion. The results obtained allow us to conclude that, if public hospitals have adequate purchase negotiation instruments and a uniform legal framework, they can achieve a good level of activity. Furthermore, public hospitals can contribute to reductions in price and price dispersion, at the same time as improving efficiency in the assignation and utilization of resources.

We give an overview on current experiments on Bose-Einstein condensation (BEC) in a one-dimensional (1D) optical lattice. We introduce measurements of ground state, tunnelling and dynamical properties as well as investigations of atom optical applications and thermodynamical properties. Measurements of the coherent atomic current in an array of Josephson junctions and the critical velocity for the breakdown of superfluid motion are discussed in detail., 16 pages, To appear in: 'Experimental Quantum Computing and Information', Proceedings of the Internation School of Physics 'Enrico Fermi', Varenna, Course CXLVIII (2001), edited by C. Monroe, P. Mataloni and F. DeMartini (IOS Press, Amsterdam)

Physical Review Letters

Physical Review Letters

We have investigated the rf output coupling of a 87Rb condensate from a Ioffe-Pritchard magnetic trap. Multiple condensates in different Zeeman states are produced, their population being varied by playing with the duration and the amplitude of the rf pulse. Both pulsed and continuous outputs (atom laser) have been observed., 12 pages, 6 figures

We present the results concerning smoking prevalence and related factors from a wider cross sectional survey of a representative sample of 5th and 8th grade schoolchildren (10-11 and 13-14 years old respectively) in the city of Barcelona, Spain. The survey was done in the 1986-87 school year. During this period of life there is an increase in the presence of smoking in the social environment and a rise in use of tobacco by schoolchildren, paralleled by a modification of their personal attitudes, radically opposed to smoking in the younger ages. The construction of a model to separate smokers and non smokers on the basis of predictive variables is attempted through discriminant analysis. Results suggest the most important factors are socioeconomic (lower socioeconomic status, higher amounts of pocket money), environmental (having siblings or friends who smoke), attitudinal (agreeing with certain sentences such as "smoking makes you feel good", "smoking is not as harmful as they say", "smokers are not more interesting persons", "I like the smell of tobacco" and "I'll probably smoke in the future") and related to other health associated behaviors (lower physical activity levels, having got drunk). These data will help in the design of school health programs addressing smoking prevention and provide baseline information for their evaluation.

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 $\Gamma$. 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., Comment: 6 + 12 pages, 4 + 6 figures, 57 references

We report on the direct observation of an oscillating atomic current in a one-dimensional array of Josephson junctions realized with an atomic Bose-Einstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly coupled by the interwell barriers. The coherence of multiple tunneling between adjacent wells is continuously probed by atomic interference. The square of the small-amplitude oscillation frequency is proportional to the microscopic tunneling rate of each condensate through the barriers and provides a direct measurement of the Josephson critical current as a function of the intermediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and lays a bridge between the condensate dynamics and the physics of discrete nonlinear media.

In search of non-classical correlations between momentum components of a Bose-Einstein condensate (BEC), we have investigated atom interferometers of trapped and free-falling BEC, obtaining a quantitative description of the spacing of interference fringes observed at output ports.

Understanding the effect of interactions in the phase evolution of expanding atomic Bose Einstein condensates is fundamental to describe 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 $^{87}$Rb 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 wavepackets overlap., 10 pages, 14 figures; published version

We report on the formation of heteronuclear quantum droplets in an attractive bosonic mixture of 41K and 87Rb. We observe long-lived self-bound states, both in free space and in an optical waveguide. In the latter case, the dynamics under the effect of a species-dependent force confirms their bound nature. By tuning the interactions from the weakly to the strongly attractive regime, we study the transition from expanding to localized states, in both geometries. We compare the experimental results with beyond mean-field theory and we find a good agreement in the full range of explored interactions. Our findings open up the production of long-lived droplets with important implications for further research., Comment: 9 pages, 7 figures

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., 6 pages, 4 figures + Supplemental Material

We report on the direct observation of the electromagnetically induced transparency (EIT) lineshape of cold Rb-87 atoms above and below the transition temperature for Bose-Einstein condensation (BEC). Similar results are observed in both temperature regimes, with an absorption reduction of about 60%. Good agreement with a theoretical model is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

International audience; Accumulation of toxic amyloid oligomers is a key feature in the pathogenesis of amyloid-related diseases. Formation of mature amyloid fibrils is one defense mechanism to neutralize toxic prefibrillar oligomers. This mechanism is notably influenced by apolipoprotein E variants. Cells that produce mature amyloid fibrils to serve physiological functions must exploit specific mechanisms to avoid potential accumulation of toxic species. Pigment cells have tuned their endosomes to maximize the formation of functional amyloid from the protein PMEL. Here, we show that ApoE is associated with intraluminal vesicles (ILV) within endosomes and remain associated with ILVs when they are secreted as exosomes. ApoE functions in the ESCRT-independent sorting mechanism of PMEL onto ILVs and regulates the endosomal formation of PMEL amyloid fibrils in vitro and in vivo. This process secures the physiological formation of amyloid fibrils by exploiting ILVs as amyloid nucleating platforms.

Collective excitations have been observed in a Rb-87 Bose condensate, confined in a magneto-static, elongated, harmonic trap. We have measured the frequency of two different modes with zero angular momentum along the symmetry axis of the trap. Both the frequencies are in good agreement with the values predicted by the hydrodynamic theory of superfluids holding in the Thomas-Fermi regime.

We have performed time-domain interferometry experiments with matter waves trapped in an harmonic potential above and below the Bose-Einstein phase transition. We interrogate the atoms according to the method of separated oscillating fields, with a sequence of two radio-frequency pulses, separated by a time delay T. We observe the oscillation of the population between two internal Zeeman states, as a function of the delay T. We find a strong depletion of the interference fringes for both the Bose condensates and the thermal clouds above condensation, even at very short times, when the clouds are still overlapping. Actually, we explain the observed loss of contrast in terms of phase patterns imprinted by the relative motion, as a consequence of the entanglement between the internal and external states of the trapped atoms., 4 pages, 3 figures

We create Bose-Einstein condensates of 87-rubidium in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the BEC and accounts for the main features of the observed behavior., Comment: 4 pages, including figures

Two 87Rb condensates (F=2, m_f=2 and m_f=1) are produced in highly displaced harmonic traps and the collective dynamical behaviour is investigated. The mutual interaction between the two condensates is evidenced in the center-of-mass oscillations as a frequency shift of 6.4(3)%. Calculations based on a mean-field theory well describe the observed effects of periodical collisions both on the center-of-mass motion and on the shape oscillations., 5 pages, 3 figures, revtex - revised version