Recent work in atom optics has led to enormous progress in the study of quantum chaos and has addressed a broad range of problems in quantum transport, traditionally studied in the context of condensed matter physics. This issue brings together the various researchers working in the border domain between atom optics and solid state physics and focuses on atomic motion in light fields in a regime that is dominated by quantum effects. The topics discussed in this issue include: • quantum effects of atomic motion in light fields; • quantum chaos in time dependent lattices; • tunnelling in stationary or time-dependent lattices; • Wannier-Stark ladder and Bloch oscillations; • atomic band structures; • many-body effects on transport in optical lattices; • effects of decoherence on quantum transport; • weak and dynamical localization. At this point we take the opportunity to express our gratitude to the authors of the papers of this issue and the reviewers for their efforts in preparing and ensuring the high quality of the state of the art presentation.
Recent work in atom optics has led to enormous progress in the study of quantum chaos and has addressed a broad range of problems in quantum transport, traditionally studied in the context of condensed matter physics. This issue brings together the various researchers working in the border domain between atom optics and solid state physics and focuses on atomic motion in light fields in a regime that is dominated by quantum effects. The topics discussed in this issue include: • quantum effects of atomic motion in light fields; • quantum chaos in time dependent lattices; • tunnelling in stationary or time-dependent lattices; • Wannier-Stark ladder and Bloch oscillations; • atomic band structures; • many-body effects on transport in optical lattices; • effects of decoherence on quantum transport; • weak and dynamical localization. At this point we take the opportunity to express our gratitude to the authors of the papers of this issue and the reviewers for their efforts in preparing and ensuring the high quality of the state of the art presentation.
Experiments on atomic Bose-Einstein condensates inside quasi-one-dimensional optical lattices and related developments in the realization of atom lasers are currently at the frontiers in atomic physics. We give a short review of theoretical progress in evaluating the coherent transport of matter in such configurations, which has been based on an adaptation of the Wannier function representation of quasi-particle states in periodic potentials and on the use of advanced numerical methods for the solution of the time-dependent Gross-Pitaevskii equation. We present various methods by which the band structure of the elementary excitations of a periodic condensate may be probed and describe in terms of Bloch oscillations the coherent emission of matter pulses from a condensate inside an optical lattice under the force of gravity. A harmonic force can be applied to a condensate inside a magnetic trap by a rapid displacement of the center of the trap and a transition of the condensate from superfluid to dissipative behavior is driven by superposing an optical lattice. Finally, in the superfluid regime the combination of a constant force and a harmonic force in the presence of an optical lattice drives Josephson-type oscillations of the condensate, leading to observable resonances and multimode behavior.
One of the most active areas in atomic, molecular and optical physics is the use of ultracold atomic gases in optical lattices to simulate the behaviour of electrons in condensed matter systems. The larger mass, longer length scale, and tuneable interactions in these systems allow the dynamics of atoms moving in these systems to be followed in real time, and resonant light scattering by the atoms allows this motion to be probed on a microscopic scale using site-resolved imaging. This book reviews the physics of Hubbard-type models for both bosons and fermions in an optical lattice, which give rise to a rich variety of insulating and conducting phases depending on the lattice properties and interparticle interactions. It also discusses the effect of disorder on the transport of atoms in these models, and the recently discovered phenomenon of many-body localization. It presents several examples of experiments using both density and momentum imaging and quantum gas microscopy to study the motion of atoms in optical lattices. These illustrate the power and flexibility of ultracold-lattice analogues for exploring exotic states of matter at an unprecedented level of precision.
One of the most active areas in atomic, molecular and optical physics is the use of ultracold atomic gases in optical lattices to simulate the behaviour of electrons in condensed matter systems. The larger mass, longer length scale, and tuneable interactions in these systems allow the dynamics of atoms moving in these systems to be followed in real time, and resonant light scattering by the atoms allows this motion to be probed on a microscopic scale using site-resolved imaging. This book reviews the physics of Hubbard-type models for both bosons and fermions in an optical lattice, which give rise to a rich variety of insulating and conducting phases depending on the lattice properties and interparticle interactions. It also discusses the effect of disorder on the transport of atoms in these models, and the recently discovered phenomenon of many-body localization. It presents several examples of experiments using both density and momentum imaging and quantum gas microscopy to study the motion of atoms in optical lattices. These illustrate the power and flexibility of ultracold-lattice analogues for exploring exotic states of matter at an unprecedented level of precision.
The transport of quantum particles in non ideal material media (eg the conduction of electrons in an imperfect crystal) is strongly affected by scattering from impurities of the medium. Even for a weak disorder, semi-classical theories, such as those based on the Boltzmann equation for matter-waves scattering from the impurities, often fail to describe transport properties and full quantum approaches are necessary. The properties of the quantum systems are of fundamental interest as they show intriguing and non-intuitive phenomena that are not yet fully understood such as Anderson localization, percolation, disorder-driven quantum phase transitions and the corresponding Bose-glass or spin-glass phases. Understanding quantum transport in amorphous solids is one of the main issues in this context, related to electric and thermal conductivities. Ultracold atomic gases can now be considered to revisit the problem of quantum conductivity and quantum transport under unique control possibilities. Dilute atomic Bose-Einstein condensates (BEC) and degenerate Fermi gases (DFG) are produced routinely taking advantage of the recent progress in cooling and trapping of neutral atoms. Transport has been widely investigated in controlled potentials with no defects, for instance periodic potentials (optical lattices). Controlled disordered potentials can also be produced with various techniques such as the use of magnetic traps designed on atomic chips with rough wires, the use of localized impurity atoms, the use of radio-frequency fields or the use of optical potentials. This recently lead to the observation of the Anderson Localisation of a BEC and the measurement of the diffusion coefficient of a 2D gaz in the presence of disorder.
From time to time in physics, single technical achievements have spawned an explosion of research activity and have led to the genesis of entirely new avenues of investigation. Precisely this occurred in the field of quantum gases - the topic of this Focus Issue - following the achievement of Bose-Einstein condensation in a dilute alkali gas in 1995. These experiments built on the foundational work on quantum fluids in dense systems, such as superfluid helium, and the technical achievements of laser cooling in atomic physics. Dilute quantum gases have already proved to be an incredibly fertile ground for exploring a wide range of macroscopic quantum phenomena. The rapid pace of experimental discovery and theoretical advance is evident and every year continues to bring significant achievements. A great advantage is that microscopic observations can be made directly and compared with the predictions of many-body theoretical formulations founded on interaction parameters which are completely determined - something which is not possible in their dense fluid counterparts. This Focus Issue brings together papers which cover many of the topical aspects of quantum gases: optical lattices, quantum degenerate fermions, quantum atom optics, molecular Bose-Einstein condensation, vorticity, and quantum fluctuations in systems of reduced dimensionality. One pervasive theme is the flexibility which arises from the ability to control the interactions, even dynamically if necessary. In quantum gases, this can be effected in two ways, either by changing the internal nature of the pairwise potentials by a Feshbach resonance, or by changing the nature of external potentials in which the atoms are confined and supported against gravity. The external potential may be used to spin gases to high vorticity, imprint on the system a periodic optical lattice potential, or even change the effective dimensionality. Optical lattices are particularly well represented in this Focus Issue. This is where there is the strongest connection with the physics of solids and strongly correlated fluids. Interest in optical lattices is partly due to the recent experimental demonstration that in these systems one can study the quantum phase transition from a Mott insulator, where the atoms are localized to individual sites of the optical potential, to a superfluid phase with long-range order. In contrast to a condensed matter system, the transition can be easily dynamically controlled since it is induced by simply varying the depth of the optical potential. Another area of focused interest is in fermionic gases where there is an ongoing effort, both experimentally and theoretically, to observe and characterize the high-temperature superfluid transition that should occur with enhanced pairwise interactions. If realized, this quantum system would allow experimental investigation of the crossover from Bose-Einstein condensation of dilute weakly-interacting composite bosons to the superconducting-like transition that occurs in a system of weakly interacting fermions. The topics of this Focus Issue represent well the building blocks of quantum gas studies which should allow the exploration of a wide range of macroscopic quantum phenomena in a highly controllable and clean system in which the effects of disorder may be completely absent. Given the recent progress, it will be intriguing to see where this field leads in the future. Focus on Quantum Gases Contents Anisotropic dissipation of superfluid flow in a periodically dressed Bose-Einstein condensate D M Stamper-Kurn Rapidly rotating Bose-Einstein condensates in anharmonic potentials G M Kavoulakis and Gordon Baym Feshbach resonances and collapsing Bose-Einstein condensates J N Milstein, C Menotti and M J Holland Three-body recombination of cold fermionic atoms H Suno, B D Esry and Chris H Greene Bogoliubov spectrum and Bragg spectroscopy of elongated Bose-Einstein condensates C Tozzo and F Dalfovo Quantum atom optics with Bose-Einstein condensates Klaus Mølmer Creation of effective magnetic fields in optical lattices: the Hofstadter butterfly for cold neutral atoms D Jaksch and P Zoller The Josephson frequency of resonantly coupled atomic and molecular condensates R A Duine and H T C Stoof Superfluid current disruption in a chain of weakly coupled Bose–Einstein condensates F S Cataliotti, L Fallani, F Ferlaino, C Fort, P Maddaloni and M Inguscio Bright matter wave solitons in Bose–Einstein condensates K E Strecker, G B Partridge, A G Truscott and R G Hulet Spin dynamics for bosons in an optical lattice Juan José García-Ripoll and Juan Ignacio Cirac Mean field ground state of a spin-1 condensate in a magnetic field Wenxian Zhang, Su Yi and Li You Atom resonant tunnelling through a moving barrier M L Chiofalo, M Artoni and G C La Rocca Local correlations in a strongly interacting one-dimensional Bose gas D M Gangardt and G V Shlyapnikov Shift of the molecular bound state threshold in dense ultracold Fermi gases with Feshbach resonance R Combescot Landau damping in trapped Bose condensed gases B Jackson and E Zaremba An exact reformulation of the Bose–Hubbard model in terms of a stochastic Gutzwiller ansatz Iacopo Carusotto and Yvan Castin Chemical potential standard for atomic Bose–Einstein condensates Sigmund Kohler and Fernando Sols The short-distance first-order correlation function of the interacting one-dimensional Bose gas Maxim Olshanii and Vanja Dunjko The relation between the Gross–Pitaevskii and Bogoliubov descriptions of a dilute Bose gas A J Leggett Superfluidity of Bose–Einstein condensate in an optical lattice: Landau–Zener tunnelling and dynamical instability B Wu and Q Niu Density-optimized efficiency for magneto-optical production of a stable molecular Bose–Einstein condensate Matt Mackie, Anssi Collin, Kalle-Antti Suominen and Juha Javanainen A two-atom picture of coherent atom–molecule quantum beats Bogdan Borca, D Blume and Chris H Greene Superfluid dynamics of a Bose–Einstein condensate in a periodic potential C Menotti, A Smerzi and A Trombettoni Phase diagram of two-component bosons on an optical lattice Ehud Altman, Walter Hofstetter, Eugene Demler and Mikhail D Lukin Murray J Holland University of Colorado at Boulder, USA
Quantum gases in optical lattices allow for fundamental studies in atomic and condensed-matter physics and the exploration of novel effects. After a brief introduction to the fundamentals of quantum gas experiments in optical lattices, we discuss two recent experiments focusing on driven matter waves in a one-dimensional optical lattice. The first experiment uses a tilted bichromatic optical lattice to investigate the interplay of disorder and collisional interactions in the accelerated transport of a Bose-Einstein condensate. Here, a screening effect is observed, in which the interactions effectively cancel the damping of Bloch oscillations induced by a (quasi-)disordered potential. This effect can be understood through a modification of the underlying band structure by the interactions. The second experiment studies the dynamics of a weakly trapped condensate resonantly coupled to the orbitals of a strongly confining state-selective lattice. We observe momentum distributions that correspond to matter wave diffraction from a periodic structure; however, the diffractive dynamics remain strongly linked to the internal-state Rabi oscillations. In the regime investigated, which we call the nonadiabatic regime, no diffracting potential can be defined. We show how only for much stronger coupling, the internal and external dynamics decouple, transitioning from nonadiabatic diffraction to the well-studied Kapitza-Dirac diffraction. We further investigate prospects for realizing dissipative spin models in our ultracold atomic gas experiment. To this end, we develop and test in the laboratory several possible implementations of effective spins with differential coupling to a superfluid background and examine their viability for a realization of the spin-boson model. | 94 pages