Repulsively bound atom pairs in an optical lattice

Winkler, Klaus; Thalhammer, Gregor; Lang, Florian; Grimm, Rudolf; Denschlag, Johannes Hecker; Daley, Andrew J.; Kantian, Adrian; Büchler, Hans Peter; Zoller, P.

doi:10.1038/nature04918

Cited by 562 publications

(783 citation statements)

References 31 publications

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“…For very strong attractive or repulsive interactions |U | J, however, doubly occupied sites (doublons) only decay very slowly [5,44,45] as the missing or excess energy of order U cannot easily be transferred to other particles.…”

Section: Doublon Dissolution Timementioning

confidence: 99%

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

et al. 2012

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Transport properties are among the defining characteristics of many important phases in condensed matter physics. In the presence of strong correlations they are difficult to predict even for model systems like the Hubbard model. In real materials they are in general obscured by additional complications including impurities, lattice defects or multi-band effects. Ultracold atoms in contrast offer the possibility to study transport and out-of-equilibrium phenomena in a clean and well-controlled environment and can therefore act as a quantum simulator for condensed matter systems. Here we studied the expansion of an initially confined fermionic quantum gas in the lowest band of a homogeneous optical lattice. While we observe ballistic transport for non-interacting atoms, even small interactions render the expansion almost bimodal with a dramatically reduced expansion velocity. The dynamics is independent of the sign of the interaction, revealing a novel, dynamic symmetry of the Hubbard model.In solid state physics, transport properties are among the key observables, the most prominent example being the electrical conductivity, which e.g. allows to distinguish normal conductors from insulators or superconductors. Furthermore, many of today's most intriguing solid state phenomena manifest themselves in transport properties, examples including high-temperature superconductivity, giant magnetoresistance, quantum hall physics, topological insulators and disorder phenomena. Especially in strongly correlated systems, where the interactions between the conductance electrons are important, transport properties are difficult to calculate beyond the linear response regime. In general, predicting out-of-equilibrium fermionic dynamics represents an even harder problem than the prediction of static properties like the nature of the ground state. In real solids further complications arise due to the effects of e.g. impurities, lattice defects and phonons. These complications render an experimental investigation in a clean and well controlled ultracold atom system highly desirable. While the last years have seen dramatic progress in the control of quantum gases in optical lattices [1-3], a thorough understanding of the dynamics in these systems is still lacking. Genuine dynamical experiments can not only uncover new dynamic phenomena but are also essential to gain insight into the timescales needed to achieve equilibrium in the lattice [4,5] or to adiabatically load into the lattice [6,7].Using both bosonic and fermionic [8-10] atoms, it has become possible to simulate models of strongly interacting quantum particles, for which the Hubbard model [11] * ulrich.schneider@lmu.de is probably the most important example. A major advantage of these systems compared to real solids is the possibility to change all relevant parameters in real-time by e.g. varying laser intensities or magnetic fields. While first studies of dynamical properties of both bosonic and fermionic quantum gases [12][13][14] have already been performed, a remaining...

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Section: Doublon Dissolution Timementioning

confidence: 99%

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

et al. 2012

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“…If one of the atoms tunnelled to an empty neighbouring lattice site, then this would release an energy U. But there is no reservoir that could absorb this energy so that the tunnelling is suppressed 19 . Hence, a strong reduction of U is required to melt the pure n = 2 Mott insulator.…”

Section: Ramping For Conditions Used In Fig 2dmentioning

confidence: 99%

Preparation of a quantum state with one molecule at each site of an optical lattice

et al. 2006

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U ltracold gases in optical lattices are of great interest, because these systems bear great potential for applications in quantum simulations and quantum information processing, in particular when using particles with a longrange dipole-dipole interaction, such as polar molecules 1-5 . Here we show the preparation of a quantum state with exactly one molecule at each site of an optical lattice. The molecules are produced from an atomic Mott insulator 6 with a density profile chosen such that the central region of the gas contains two atoms per lattice site. A Feshbach resonance is used to associate the atom pairs to molecules 7-14 . The remaining atoms can be removed with blast light 13,15 . The technique does not rely on the moleculemolecule interaction properties and is therefore applicable to many systems.A variety of interesting proposals for quantum information processing and quantum simulations 1-5 require as a prerequisite a quantum state of ultracold polar molecules in an optical lattice, where each lattice site is occupied by exactly one molecule. A promising strategy for the creation of such molecules is based on the association of ultracold atoms using a Feshbach resonance, or photoassociation and subsequent transfer to a much lower rovibrational level using Raman transitions 16 . If the moleculemolecule interactions are predominantly elastic and effectively repulsive, then a state with one molecule per lattice site can finally be obtained using a quantum phase transition from a superfluid to a Mott insulator by ramping up the depth of an optical lattice 6 . However, many molecular species do not have such convenient interaction properties, so alternative strategies are needed. Here, we demonstrate a technique that is independent of the molecule-molecule interaction properties. The technique relies on first forming an atomic Mott insulator and then associating molecules. Several previous experiments 15,17-20 associated molecules in an optical lattice, but none of them demonstrated the production of a quantum state with exactly one molecule per lattice site. Another interesting perspective of the state prepared here is that after Raman transitions to the rovibrational ground state, the lattice potential can be lowered to obtain a Bose-Einstein condensate (BEC) of molecules in the rovibrational ground state 21,22 . Figure 1 Schematic diagram of the molecular n = 1 state. In the core of the cloud, each lattice site is occupied by exactly n = 1 molecule (shown in green). In the surrounding shell, each site is occupied by exactly one atom (shown in red). The atoms can be removed with a blast laser. In the experiment, the number of occupied lattice sites is much larger than shown here.The behaviour of bosons in an optical lattice is described by the Bose-Hubbard hamiltonian 23 . The relevant parameters are the amplitude J for tunnelling between neighbouring lattice sites and the on-site interaction matrix element U. We create a Mott insulator 6 of atomic 87 Rb starting from an atomic BEC in an optical dipol...

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“…The third band is obtained for complex-conjugate values of k 1 and k 2 , and spans the energy interval (U, √ U 2 + 16) (for U > 0), or (− √ U 2 + 16, U ) (for U < 0). This band is the well-known Mott-Hubbard band which describes twoparticle bound states (doublons) that undergo correlated tunneling on the lattice (see, for instance, [34]). …”

Section: Tamm-hubbard Surface Statesmentioning

confidence: 99%

Tamm–Hubbard surface states in the continuum

Longhi

Valle

2013

J. Phys.: Condens. Matter

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Abstract. In the framework of the Bose-Hubbard model, we show that two-particle surface bound states embedded in the continuum (BIC) can be sustained at the edge of a semi-infinite one-dimensional tight-binding lattice for any infinitesimally-small impurity potential V at the lattice boundary. Such thresholdless surface states, that can be referred to as Tamm-Hubbard BIC states, exist provided that the impurity potential V is attractive (repulsive) and the particle-particle Hubbard interaction U is repulsive (attractive), i.e. for U V < 0.

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Repulsively bound atom pairs in an optical lattice

Cited by 562 publications

References 31 publications

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

Preparation of a quantum state with one molecule at each site of an optical lattice

Tamm–Hubbard surface states in the continuum

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