Observation of heteronuclear atomic Efimov resonances

The Efimov effect represents a cornerstone in few-body physics. Building on the recent experimental observation with ultracold atoms, we report the first experimental signature of Efimov physics in a heteronuclear system. A mixture of $^{41}$K and $^{87}$Rb atoms was cooled to few hundred nanoKelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative. We attribute the two features at negative scattering length to the existence of two kind of Efimov trimers, namely KKRb and KRbRb.Comment: 4 pages, 4 figure

Radio Frequency Selective Addressing of Localized Particles in a Periodic Potential

We study the localization and addressability of ultra cold atoms in a combined parabolic and periodic potential. Such a potential supports the existence of localized stationary states and we show that using a radio frequency field allows to selectively address the atoms in these states. This method is used to measure the energy and momentum distribution of the atoms in the localized states. We also discuss possible extensions of this scheme to address and manipulate particles in single lattice sites.Comment: 4 pages, 4 figure

Quantum normal-to-inhomogeneous superconductor phase transition in nearly two-dimensional metals

In multi-band systems, electrons from different orbitals coexist at the Fermi surface. An attractive interaction among these quasi-particles gives rise to inter-band or hybrid pairs which eventually condense in a superconducting state. These quasi-particles have a natural mismatch of their Fermi wave-vectors, $\delta k_F$, which depends on the strength of the hybridization between their orbitals. The existence of this natural scale suggests the possibility of inhomogeneous superconducting ground states in these systems, even in the absence of an applied magnetic field. Furthermore, since hybridization $V$ depends on pressure, this provides an external parameter to control the wave-vectors mismatch at the Fermi surface. In this work, we study the phase diagram of a two-dimensional, two-band metal with inter-band pairing. We show that as the mismatch between the Fermi wave-vectors of the two hybrid bands is reduced, the system presents a normal-to-inhomogeneous superconductor quantum phase transition at a critical value of the hybridization $V_c=\Delta_0$. The superconducting ground state for $V<V_c$ is characterized by a wave-vector with magnitude $|\mathbf{q}_c|=q_c=2 \Delta_0/\bar{v}_f$. Here $\Delta_0$ is the superconducting gap in the homogeneous state and $\bar{v}_f$ the average Fermi velocity. We discuss the nature of the quantum critical point (QCP) at $V_c$ and obtain the associated quantum critical exponents.Comment: 6 pages, 4 figure

Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide

We investigate the one-dimensional expansion of a Bose-Einstein condensate in an optical guide in the presence of a random potential created with optical speckles. With the speckle the expansion of the condensate is strongly inhibited. A detailed investigation has been carried out varying the experimental conditions and checking the expansion when a single optical defect is present. The experimental results are in good agreement with numerical calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure

Disorder-enhanced phase coherence in trapped bosons on optical lattices

The consequences of disorder on interacting bosons trapped in optical lattices are investigated by quantum Monte Carlo simulations. At small to moderate strengths of potential disorder a unique effect is observed: if there is a Mott plateau at the center of the trap in the clean limit, phase coherence {\it increases} as a result of disorder. The localization effects due to correlation and disorder compete against each other, resulting in a partial delocalization of the particles in the Mott region, which in turn leads to increased phase coherence. In the absence of a Mott plateau, this effect is absent. A detailed analysis of the uniform system without a trap shows that the disordered states participate in a Bose glass phase.Comment: 4 pages, 4 figure

Three fermions in a box at the unitary limit: universality in a lattice model

We consider three fermions with two spin components interacting on a lattice model with an infinite scattering length. Low lying eigenenergies in a cubic box with periodic boundary conditions, and for a zero total momentum, are calculated numerically for decreasing values of the lattice period. The results are compared to the predictions of the zero range Bethe-Peierls model in continuous space, where the interaction is replaced by contact conditions. The numerical computation, combined with analytical arguments, shows the absence of negative energy solution, and a rapid convergence of the lattice model towards the Bethe-Peierls model for a vanishing lattice period. This establishes for this system the universality of the zero interaction range limit.Comment: 6 page

Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius

We measure the absolute frequency of seven out of the nine allowed transitions between the 2$^3${\it S} and 2$^3${\it P} hyperfine manifolds in a metastable $^3$He beam by using an optical frequency comb synthesizer-assisted spectrometer. The relative uncertainty of our measurements ranges from $1\times 10^{-11}$ to $5\times 10^{-12}$, which is, to our knowledge, the most precise result for any optical $^3$He transition to date. The resulting $2^3${\it P}-2$^3${\it S} centroid frequency is $276\,702\,827\,204.8\,(2.4)$kHz. Comparing this value with the known result for the $^4$He centroid and performing {\em ab initio} QED calculations of the $^4$He-$^3$He isotope shift, we extract the difference of the squared nuclear charge radii $\delta r^2$ of $^3$He and $^4$He. Our result for $\delta r^2=1.074 (3)$ fm$^2$ disagrees by about $4\,\sigma$ with the recent determination [R. van Rooij {\em et al.}, Science {\bf 333}, 196 (2011)].Comment: 4 pages, 3 figures, 3 table

Atomic wave packet dynamics in finite time-dependent optical lattices

Atomic wave packets in optical lattices which are both spatially finite and time-dependent exhibit many striking similarities with light pulses in photonic crystals. We analytically characterize the transmission properties of such a potential geometry for an ideal gas in terms of a position-dependent band structure. In particular, we find that at specific energies, wave packets at the center of the finite lattice may be enclosed by pairs of band gaps. These act as mirrors between which the atomic wave packet is reflected, thereby effectively yielding a matter wave cavity. We show that long trapping times may be obtained in such a resonator and investigate the collapse and revival dynamics of the atomic wave packet by numerical evaluation of the Schr\"odinger equation

Physics with Coherent Matter Waves

This review discusses progress in the new field of coherent matter waves, in particular with respect to Bose-Einstein condensates. We give a short introduction to Bose-Einstein condensation and the theoretical description of the condensate wavefunction. We concentrate on the coherence properties of this new type of matter wave as a basis for fundamental physics and applications. The main part of this review treats various measurements and concepts in the physics with coherent matter waves. In particular we present phase manipulation methods, atom lasers, nonlinear atom optics, optical elements, interferometry and physics in optical lattices. We give an overview of the state of the art in the respective fields and discuss achievements and challenges for the future