We report on the experimental observation of vortex tangles in an atomic Bose-Einstein condensate (BEC) of ;{87}Rb atoms when an external oscillatory perturbation is introduced in the trap. The vortex tangle configuration is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud suppresses the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion. Instead, the cloud expands keeping the ratio between their axis constant. Turbulence in atomic superfluids may constitute an alternative system to investigate decay mechanisms as well as to test fundamental theoretical aspects in this field.

We report on the observation of the Josephson effect between two strongly interacting fermionic superfluids coupled through a thin tunneling barrier. We prove that the relative population and phase are canonically conjugate dynamical variables, coherently oscillating throughout the entire crossover from molecular Bose-Einstein condensates (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluids. We measure the plasma frequency and we extract the Josephson coupling energy, both exhibiting a non-monotonic behavior with a maximum near the crossover regime. We also observe the transition from coherent to dissipative dynamics, which we directly ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids, opening the door to the study of the dynamics of superfluid Fermi systems in the presence of strong correlations and fluctuations.The Josephson effect is a pristine example of a macroscopic quantum phenomenon, disclosing the broken symmetry associated with the superfluid state [1]. On a very fundamental level, it allows to pinpoint the most elusive part of the superfluid order parameter, the phase, through a measurable quantity, a particle current [2]. Furthermore, being based on tunneling processes, Josephson dynamics provides fundamental insights into the microscopic properties of superfluids and their robustness against dissipative phenomena [3]. Since its discovery, Josephson effect has been demonstrated for a variety of fermionic and bosonic systems [3][4][5][6][7][8][9][10][11][12]. However, it has so far eluded observation in BEC-BCS crossover superfluids [13,14] realized by ultracold Fermi gas mixtures close to a Feshbach resonance [15,16]. The interest in these systems is twofold: on the one hand, they encompass the two paradigmatic aspects of superfluidity within a single framework: Bose-Einstein condensation of tightly bound molecules and BCS superfluidity of long-range fermion pairs [13]. Moreover, in the resonant regime where the pair size matches the interparticle spacing, they exhibit universal properties, sharing analogies with other exotic strongly-correlated fermionic superfluids, from cuprate superconductors to nuclear and quark matter [17,18].In this work, we report on the observation of the Josephson effect in ultracold gases of 6 Li atom pairs across the BEC-BCS crossover. Our Josephson junction consists of two superfluid reservoirs, weakly coupled through a thin tunneling barrier. For all interaction regimes, we detect coherent oscillations of both the pair population imbalance ∆N = N L −N R and the relative phase ϕ = ϕ L −ϕ R across * Permanent address: Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, 01000 México Distrito Federal, Mexico.the junction, measured in situ and after time-of-flight expansion respectively. We prove these two observables to be dynamically conjugate [2], directly unveiling macroscopic phase coherence in these strongly-correlated fermionic superfluids. We measure th...

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 Bose-Einstein condensate-Bardeen-Cooper-Schrieffer 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-equilibrium quantum systems.

We have studied a Bose-Einstein condensate of 87 Rb atoms under an oscillatory excitation. For a fixed frequency of excitation, we have explored how the values of amplitude and time of excitation must be combined in order to produce quantum turbulence in the condensate. Depending on the combination of these parameters different behaviors are observed in the sample. For the lowest values of time and amplitude of excitation, we observe a bending of the main axis of the cloud. Increasing the amplitude of excitation we observe an increasing number of vortices. The vortex state can evolve into the turbulent regime if the parameters of excitation are driven up to a certain set of combinations. If the value of the parameters of these combinations is exceeded, all vorticity disappears and the condensate enters into a different regime which we have identified as the granular phase. Our results are summarized in a diagram of amplitude versus time of excitation in which the different structures can be identified. We also present numerical simulations of the Gross-Pitaevskii equation which support our observations.

We report on the observation of vortex formation in a Bose-Einstein condensate of 87 Rb atoms. Vortices are generated by superimposing an oscillating excitation to the trapping potential introduced by an external magnetic field. For small amplitudes of the external excitation field we observe a bending of the cloud axis. Increasing the amplitude we observe formation of a growing number of vortices in the sample. Shot-to-shot variations in both vortex number and position within the condensed cloud are observed, probably due to the intrinsic vortex nucleation dynamics. We discuss the possible formation of vortices and antivortices in the sample as well as possible mechanisms for vortex nucleation.

The shape and alignment of silver nanoparticles embedded in a glass matrix is controlled using silicon ion irradiation. Symmetric silver nanoparticles are transformed into anisotropic particles whose larger axis is along the ion beam. Upon irradiation, the surface plasmon resonance of symmetric particles splits into two resonances whose separation depends on the fluence of the ion irradiation. Simulations of the optical absorbance show that the anisotropy is caused by the deformation and alignment of the nanoparticles, and that both properties are controlled with the irradiation fluence. *

We report on the creation of three-vortex clusters in a 87 Rb Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulation, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation, and as a vortex-antivortex-vortex cluster. The linear configurations are very likely the first experimental signatures of predicted stationary vortex clusters.

We use a gray molasses operating on the D 1 atomic transition to produce degenerate quantum gases of 6 Li with a large number of atoms. This sub-Doppler cooling phase allows us to lower the initial temperature of 10 9 atoms from 500 to 40 μK in 2 ms. We observe that D 1 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 5 × 10 5 molecules and weakly interacting degenerate Fermi gases of 7 × 10 5 atoms at T /T F < 0.1 with a typical experimental duty cycle of 11 s.