Creation of optical speckle by randomizing a vortex-lattice.

We investigate the number of vortices embedded in a carrier beam needed to produce a speckle pattern and the necessary conditions in terms of their initial distribution and topological charges. A spatial light modulator is used to imprint arrays of vortices in a Gaussian beam, which is propagated in free space for a given distance and then focused in order to induce interaction among the vortices in the focal region. The resulting optical field is analyzed after propagation up to a transverse plane where the carrier beam would recover its initial size in the absence of vortices. The role of different control parameters for obtaining ordered and disordered patterns is discussed. Our experimental study is complemented with a thorough numerical analysis, from which the statistical properties of the disordered patterns are characterized, and the conditions for obtaining well-developed speckle are determined. We also discuss the creation and annihilation of vortex pairs, depending on the initial conditions.

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 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.

Emergence of turbulence in an oscillating bose-einstein condensate.

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.

Optical transmission through multilayered structures.

A simple procedure is presented for computing optical transmission through planar layered structures when interference effects can be neglected, but all multiple internal reflections are taken into account. Closed form solutions are given for a single absorbing layer on a nonabsorbing substrate and for two identical absorbing layers on either side of a nonabsorbing substrate.