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Castelldefels, Spain

Struck J.,University of Hamburg | Weinberg M.,University of Hamburg | Olschlager C.,University of Hamburg | Windpassinger P.,University of Hamburg | And 9 more authors.
Nature Physics | Year: 2013

Magnetism plays a key role in modern science and technology, but still many open questions arise from the interplay of magnetic many-body interactions. Deeper insight into complex magnetic behaviour and the nature of magnetic phase transitions can be obtained from, for example, model systems of coupled XY and Ising spins. Here, we report on the experimental realization of such a coupled system with ultracold atoms in triangular optical lattices. This is accomplished by imposing an artificial gauge field on the neutral atoms, which acts on them as a magnetic field does on charged particles. As a result, the atoms show persistent circular currents, the direction of which provides an Ising variable. On this, the tunable staggered gauge field, generated by a periodic driving of the lattice, acts as a longitudinal field. Further, the superfluid ground state presents strong analogies with the paradigm example of the fully frustrated XY model on a triangular lattice. © 2013 Macmillan Publishers Limited.

Novotny L.,University of Rochester | Van Hulst N.,Institute Of Ciencies Fotoniques | Van Hulst N.,Catalan Institution for Research and Advanced Studies
Nature Photonics | Year: 2011

Optical antennas are devices that convert freely propagating optical radiation into localized energy, and vice versa. They enable the control and manipulation of optical fields at the nanometre scale, and hold promise for enhancing the performance and efficiency of photodetection, light emission and sensing. Although many of the properties and parameters of optical antennas are similar to their radiowave and microwave counterparts, they have important differences resulting from their small size and the resonant properties of metal nanostructures. This Review summarizes the physical properties of optical antennas, provides a summary of some of the most important recent developments in the field, discusses the potential applications and identifies the future challenges and opportunities. © 2011 Macmillan Publishers Limited. All rights reserved.

Hauke P.,Institute For Quantenoptik Und Quanteninformation | Hauke P.,University of Innsbruck | Lewenstein M.,Institute Of Ciencies Fotoniques | Lewenstein M.,Catalan Institution for Research and Advanced Studies | Eckardt A.,Max Planck Institute For Physik Komplexer Systeme
Physical Review Letters | Year: 2014

We propose a simple scheme for tomography of band-insulating states in one- and two-dimensional optical lattices with two sublattice states. In particular, the scheme maps out the Berry curvature in the entire Brillouin zone and extracts topological invariants such as the Chern number. The measurement relies on observing - via time-of-flight imaging - the time evolution of the momentum distribution following a sudden quench in the band structure. We consider two examples of experimental relevance: the Harper model with π flux and the Haldane model on a honeycomb lattice. Moreover, we illustrate the performance of the scheme in the presence of a parabolic trap, noise, and finite measurement resolution. © 2014 American Physical Society.

Institute Of Ciencies Fotoniques, Catalan Institution for Research and Advanced Studies | Date: 2011-02-11

An optical parametric oscillator including a nonlinear crystal pumped by a laser source and an optical resonator, including an optical interferometer, which determines a level of output coupling of the oscillator, allowing high stability, broad wavelength tuning, and output power level optimization.

Austin D.R.,Institute Of Ciencies Fotoniques | Biegert J.,Institute Of Ciencies Fotoniques | Biegert J.,Catalan Institution for Research and Advanced Studies
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We derive analytic expressions for the spectral amplitude of high-order harmonic generation from a single atom using the strong-field approximation (SFA). We demonstrate good agreement with time-dependent Schrödinger equation calculations, including the dependence on the drive wavelength across the range 566-2260 nm. Previous claims of a discrepancy in the drive wavelength scaling ignore changes in the timing of trajectories corresponding to a fixed harmonic photon energy. Under this condition, tunnel ionization is shown to play the most important role for the short trajectories. The established agreement enables us to use the SFA to predict that the intensity at the classical cutoff scales inversely with the ninth power of the drive wavelength in the high photon energy limit when the Coulomb singularity dominates the recombination amplitude. © 2012 American Physical Society.

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