@article{1044, abstract = {Control over all internal and external degrees of freedom of molecules at the level of single quantum states will enable a series of fundamental studies in physics and chemistry1,2. In particular, samples of ground-state molecules at ultralow temperatures and high number densities will facilitate new quantum-gas studies3 and future applications in quantum information science4. However, high phase-space densities for molecular samples are not readily attainable because efficient cooling techniques such as laser cooling are lacking. Here we produce an ultracold and dense sample of molecules in a single hyperfine level of the rovibronic ground state with each molecule individually trapped in the motional ground state of an optical lattice well. Starting from a zero-temperature atomic Mott-insulator state with optimized double-site occupancy6, weakly bound dimer molecules are efficiently associated on a Feshbach resonance7 and subsequently transferred to the rovibronic ground state by a stimulated four-photon process with >50% efficiency. The molecules are trapped in the lattice and have a lifetime of 8 s. Our results present a crucial step towards Bose-Einstein condensation of ground-state molecules and, when suitably generalized to polar heteronuclear molecules, the realization of dipolar quantum-gas phases in optical lattices8-10.}, author = {Danzl, Johann G and Mark, Manfred and Haller, Elmar and Gustavsson, Mattias and Hart, Russell and Aldegunde, Jesus and Hutson, Jeremy and Nägerl, Hanns}, journal = {Nature Physics}, number = {4}, pages = {265 -- 270}, publisher = {Nature Publishing Group}, title = {{An ultracold high-density sample of rovibronic ground-state molecules in an optical lattice}}, doi = {10.1038/nphys1533}, volume = {6}, year = {2010}, } @article{1045, abstract = {We report on the observation of confinement-induced resonances in strongly interacting quantum-gas systems with tunable interactions for one- and two-dimensional geometry. Atom-atom scattering is substantially modified when the s-wave scattering length approaches the length scale associated with the tight transversal confinement, leading to characteristic loss and heating signatures. Upon introducing an anisotropy for the transversal confinement we observe a splitting of the confinement-induced resonance. With increasing anisotropy additional resonances appear. In the limit of a two-dimensional system we find that one resonance persists.}, author = {Haller, Elmar and Mark, Manfred and Hart, Russell and Danzl, Johann G and Reichsöllner, Lukas and Melezhik, Vladimir and Schmelcher, Peter and Nägerl, Hanns}, journal = {Physical Review Letters}, number = {15}, publisher = {American Physical Society}, title = {{Confinement-induced resonances in low-dimensional quantum systems}}, doi = {10.1103/PhysRevLett.104.153203}, volume = {104}, year = {2010}, } @article{1049, abstract = {Quantum many-body systems can have phase transitions even at zero temperature; fluctuations arising from Heisenbergĝ€™s uncertainty principle, as opposed to thermal effects, drive the system from one phase to another. Typically, during the transition the relative strength of two competing terms in the systemĝ€™s Hamiltonian changes across a finite critical value. A well-known example is the Mottĝ€" Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry, a novel type of quantum phase transition may be induced and driven by an arbitrarily weak perturbation to the Hamiltonian. Here we observe such an effectĝ€"the sineĝ€"Gordon quantum phase transition from a superfluid Luttinger liquid to a Mott insulatorĝ€ "in a one-dimensional quantum gas of bosonic caesium atoms with tunable interactions. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sineĝ€"Gordon model. We trace the phase boundary all the way to the weakly interacting regime, where we find good agreement with the predictions of the one-dimensional Boseĝ€"Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality and transport phenomena beyond Hubbard-type models in the context of ultracold gases.}, author = {Haller, Elmar and Hart, Russell and Mark, Manfred and Danzl, Johann G and Reichsöllner, Lukas and Gustavsson, Mattias and Dalmonte, Marcello and Pupillo, Guido and Nägerl, Hanns}, journal = {Nature}, number = {7306}, pages = {597 -- 600}, publisher = {Nature Publishing Group}, title = {{Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons}}, doi = {10.1038/nature09259}, volume = {466}, year = {2010}, } @article{1047, abstract = {Particles in a perfect lattice potential perform Bloch oscillations when subject to a constant force, leading to localization and preventing conductivity. For a weakly interacting Bose-Einstein condensate of Cs atoms, we observe giant center-of-mass oscillations in position space with a displacement across hundreds of lattice sites when we add a periodic modulation to the force near the Bloch frequency. We study the dependence of these "super" Bloch oscillations on lattice depth, modulation amplitude, and modulation frequency and show that they provide a means to induce linear transport in a dissipation-free lattice.}, author = {Haller, Elmar and Hart, Russell and Mark, Manfred and Danzl, Johann G and Reichsöllner, Lukas and Nägerl, Hanns}, journal = {Physical Review Letters}, number = {20}, publisher = {American Physical Society}, title = {{Inducing transport in a dissipation-free lattice with super bloch oscillations}}, doi = {10.1103/PhysRevLett.104.200403}, volume = {104}, year = {2010}, } @article{1046, abstract = {The phenomenon of matter-wave interference lies at the heart of quantum physics. It has been observed in various contexts in the limit of non-interacting particles as a single-particle effect. Here we observe and control matter-wave interference whose evolution is driven by interparticle interactions. In a multi-path matter-wave interferometer, the macroscopic manybody wave function of an interacting atomic Bose-Einstein condensate develops a regular interference pattern, allowing us to detect and directly visualize the effect of interaction-induced phase shifts. We demonstrate control over the phase evolution by inhibiting interaction-induced dephasing and by refocusing a dephased macroscopic matter wave in a spin-echo-type experiment. Our results show that interactions in a many-body system lead to a surprisingly coherent evolution, possibly enabling narrow-band and high-brightness matterwave interferometers based on atom lasers.}, author = {Gustavsson, Mattias and Haller, Elmar and Mark, Manfred and Danzl, Johann G and Hart, Russell and Daley, Andrew and Nägerl, Hanns}, journal = {New Journal of Physics}, publisher = {IOP Publishing Ltd.}, title = {{Interference of interacting matter waves}}, doi = {10.1088/1367-2630/12/6/065029}, volume = {12}, year = {2010}, }