Microscopic theory of photonic band gaps in optical lattices

We propose a microscopic model to describe the scattering of light by atoms in optical lattices. The model is shown to efficiently capture Bragg scattering, spontaneous emission and photonic band gaps. A connection to the transfer matrix formalism is established in the limit of a one-dimensional optical lattice, and we find the two theories to yield results in good agreement. The advantage of the microscopic model is, however, that it suits better for studies of finite-size and disorder effects.Comment: 5 pages, 6 figure

Feshbach resonances in mixtures of ultracold 6^6Li and 87^{87}Rb gases

We report on the observation of two Feshbach resonances in collisions between ultracold $^6$Li and $^{87}$Rb atoms in their respective hyperfine ground states $|F,m_F>=|1/2,1/2>$ and $|1,1>$. The resonances show up as trap losses for the $^6$Li cloud induced by inelastic Li-Rb-Rb three-body collisions. The magnetic field values where they occur represent important benchmarks for an accurate determination of the interspecies interaction potentials. A broad Feshbach resonance located at 1066.92 G opens interesting prospects for the creation of ultracold heteronuclear molecules. We furthermore observe a strong enhancement of the narrow p-wave Feshbach resonance in collisions of $^6$Li atoms at 158.55 G in the presence of a dense $^{87}$Rb cloud. The effect of the $^{87}$Rb cloud is to introduce Li-Li-Rb three-body collisions occurring at a higher rate than Li-Li-Li collisions.Comment: 4 pages, 3 figure

The Atomic Lighthouse Effect

We investigate the deflection of light by a cold atomic cloud when the light-matter interaction is locally tuned via the Zeeman effect using magnetic field gradients. This "lighthouse" effect is strongest in the single-scattering regime, where deviation of the incident field is largest. For optically dense samples, the deviation is reduced by collective effects, as the increase in linewidth leads to a decrease of the magnetic field efficiency

Radiofrequency spectroscopy of 6^6Li p-wave molecules: towards photoemission spectroscopy of a p-wave superfluid

Understanding superfluidity with higher order partial waves is crucial for the understanding of high-$T_c$ superconductivity. For the realization of a superfluid with anisotropic order parameter, spin-polarized fermionic lithium atoms with strong p-wave interaction are the most promising candidates to date. We apply rf-spectroscopy techniques that do not suffer from severe final-state effects \cite{Perali08} with the goal to perform photoemission spectroscopy on a strongly interacting p-wave Fermi gas similar to that recently applied for s-wave interactions \cite{Stewart08}. Radiofrequency spectra of both quasibound p-wave molecules and free atoms in the vicinity of the p-wave Feshbach resonance located at 159.15\,G \cite{Schunck05} are presented. The observed relative tunings of the molecular and atomic signals in the spectra with magnetic field confirm earlier measurements realized with direct rf-association \cite{Fuchs08}. Furthermore, evidence of bound molecule production using adiabatic ramps is shown. A scheme to observe anisotropic superfluid gaps, the most direct proof of p-wave superfluidity, with 1d-optical lattices is proposed.Comment: 5 pages, 3 figure

Mirror-assisted coherent backscattering from the Mollow sidebands

In front of a mirror, the radiation of weakly driven large disordered clouds presents an interference fringe in the backward direction, on top of an incoherent background. Although strongly driven atoms usually present little coherent scattering, we here show that the mirror-assisted version can produce high contrast fringes, for arbitrarily high saturation parameters. The contrast of the fringes oscillates with the Rabi frequency of the atomic transition and the distance between the mirror and the atoms, due to the coherent interference between the carrier and the Mollow sidebands of the saturated resonant fluorescence spectrum emitted by the atoms. The setup thus represents a powerful platform to study the spectral properties of ensembles of correlated scatterers

Mode-locked Bloch oscillations in a ring cavity

We present a new technique for stabilizing and monitoring Bloch oscillations of ultracold atoms in an optical lattice under the action of a constant external force. In the proposed scheme, the atoms also interact with a unidirectionally pumped optical ring cavity whose one arm is collinear with the optical lattice. For weak collective coupling, Bloch oscillations dominate over the collective atomic recoil lasing instability and develop a synchronized regime in which the atoms periodically exchange momentum with the cavity field.Comment: 7 pages, 5 figure