The route toward a Bose-Einstein condensate of dipolar molecules requires the ability to efficiently associate dimers of different chemical species and transfer them to the stable rovibrational ground state. Here, we report on recent spectroscopic measurements of two weakly bound molecular levels and newly observed narrow d-wave Feshbach resonances. The data are used to improve the collisional model for the Bose-Bose mixture 41K87Rb, among the most promising candidates to create a molecular dipolar BEC.
We study the collisional decay of a strongly driven Bose-Einstein condensate oscillating between two momentum modes. The resulting products of the decay are found to strongly deviate from the usual s-wave halo. Using a stochastically seeded classical field method we simulate the collisional manifold. These results are also explained by a model of colliding Bloch states.
We study an ultracold Bose gas in the presence of 1D disorder for repulsive inter-atomic interactions varying from zero to the Thomas-Fermi regime. We show that for weak interactions the Bose gas populates a finite number of localized single-particle Lifshits states, while for strong interactions a delocalized disordered Bose-Einstein condensate is formed. We discuss the schematic quantum-state diagram and derive the equations of state for various regimes.
We apply the truncated Wigner method to the process of three-body recombination in ultracold Bose gases. We find that within the validity regime of the Wigner truncation for two-body scattering, three-body recombination can be treated using a set of coupled stochastic differential equations that include diffusion terms, and can be simulated using known numerical methods. As an example we investigate the behaviour of a simple homogeneous Bose gas.
We consider the generation of longitudinal phonons in an elongated Bose-condensed gas at zero temperature due to parametric resonance as a result of the modulation of the transverse trap frequency. The nonlinear temporal evolution with account of the phonon-phonon interaction leads self-consistently to the formation of the stationary state with the macroscopic occupation of a single phonon quantum state.
Starting from one-dimensional Mott Insulators, we use a bichromatic optical lattice to add controlled disorder to an ideal optical crystal where bosonic atoms are pinned by repulsive interactions. Increasing disorder, we observe a broadening of the Mott Insulator resonances and the transition to an insulating state with a flat density of excitations, suggesting the formation of a Bose-Glass.
Dynamical Schrödinger cats can be formed when a one-dimensional attractive Bose-gas cloud is scattered off a potential barrier. Once formed, these objects are stable in time. The phenomenon and its mechanism -- transformation of kinetic energy to internal energy of the scattered atomic cloud -- are obtained by solving the time-dependent many-boson Schrödinger equation. Implications are discussed.
Scattering phase shifts obtained from 87Rb Bose-gas collision experiments are used to reconstruct effective potentials resulting, self-consistently, in the same scattering events observed in the experiments at a particular energy. We have found that the interaction strength close to the origin suddenly changes from repulsion to attraction when the collision energy crosses, from below, the l=2 shape resonance position at E = 275 mikroK. This observation may be utilized in outlining future Bose-gas collision experiments.
The properties of ultracold atomic Bose-Fermi mixtures in external potentials are investigated and the existence of gap solitons of Bose-Fermi mixtures in optical lattices demonstrated. Using a self-consistent approach we compute the energy spectrum and show that gap solitons can be viewed as matter wave realizations of quantum dots (anti-dots) with the bosonic density playing the role of trapping (expulsive) potential for the fermions. The fermionic states trapped in the condensate are shown to be at the bottom of the Fermi sea and therefore well protected from thermal decoherence. Energy lev…
We investigate magnetic properties of Mott-insulating phases of ultracold Bose and Fermi spinor gases in optical lattices. We consider in particular the F=2 Bose gas, and the F=3/2 and F=5/2 Fermi gases. We derive effective spin Hamiltonians for one and two atoms per site and discuss the possibilities of manipulating the magnetic properties of the system using optical Feshbach resonances. We discuss low temperature quantum phases of a 87Rb gas in the F=2 hyperfine state, as well as possible realizations of high spin Fermi gases with either 6Li or 132Cs atoms in the F=3/2 state, and with 173Yb …
The relative importance of density and phase fluctuations in ultracold one dimensional atomic Bose gases is investigated. By defining appropriate characteristic temperatures for their respective onset, a broad experimental regime is found, where density fluctuations set in at a lower temperature than phase fluctuations. This is in stark contrast to the usual experimental regime explored up to now, in which phase fluctuations are largely decoupled from density fluctuations, a regime also recovered in this work as a limiting case. Observation of the novel regime of dominant density fluctuations …
Ultracold confined one-dimensional atomic gases are predicted to support dark soliton solutions arising from a nonlinear Schrödinger equation of suitable nonlinearity. In weakly-interacting (high density) gases, the nonlinearity is cubic, whereas an approximate model for describing the behaviour of strongly - interacting (low density) gases is one characterized by a quintic nonlinearity. We use an approximate analytical expression for the form of the nonlinearity in the intermediate regimes to show that, near the crossover between the two different regimes, the soliton is predicted and numeric…
We investigate bright matter-wave solitons in the presence of a spatially varying nonlinearity. It is demonstrated that a translation mode is excited due to the spatial inhomogeneity and its frequency is derived analytically and also studied numerically. Both cases of purely one-dimensional and ``cigar-shaped'' condensates are studied by means of different mean-field models, and the oscillation frequencies of the pertinent solitons are found and compared with the results obtained by the linear stability analysis.Numerical results are shown to be in very good agreement with the corresponding an…
We predict the resonance enhanced magnetic field dependence of atom-dimer relaxation and three-body recombination rates in a $^{87}$Rb Bose-Einstein condensate (BEC) close to 1007 G. Our exact treatments of three-particle scattering explicitly include the dependence of the interactions on the atomic Zeeman levels. The Feshbach resonance distorts the entire diatomic energy spectrum causing interferences in both loss phenomena. Our two independent experiments confirm the predicted recombination loss over a range of rate constants that spans four orders of magnitude.
We separate a Bose-Einstein condensate into an array of 2D sheets using a 1D optical lattice, and then excite quantized vibrational motion in the direction normal to the sheets. Collisions between atoms induce vibrational de-excitation, transferring the large excitation energy into back-to-back outgoing atoms, imaged as rings in the 2D plane. The ring diameters correspond to vibrational energy level differences, and edge-on imaging allows identification of the final vibrational states. Time dependence of these data provides a nearly complete characterization of the decay process including the …
A mechanism for the formation of a new type of stationary state with macroscopical number of phonons in condensed atomic gases is proposed. This mechanism is based on generating longitudinal phonons as a result of parametric resonance caused by a permanent modulation of the transverse trap frequency in an elongated trap. The phonon-phonon interaction predetermines the self-consistent evolution which is completed with macroscopic population of one from all levels within the energy interval of parametric amplification. This level proves to be shifted to the edge of this interval. All other level…
We discuss in detail the experimental investigation of thermally induced fluctuations of the relative phase between two weakly coupled Bose-Einstein condensates. In analogy to superconducting Josephson junctions, the weak coupling originates from a tunneling process through a potential barrier which is obtained by trapping the condensates in an optical double-well potential. The observed fluctuations of the relative phase are in quantitative agreement with a many body two mode model at finite temperature. The agreement demonstrates the possibility of using the phase fluctuation measurements in…
We study the thermodynamics of ultracold Bose atoms in optical lattices by numerically diagonalizing the mean-field Hamiltonian of the Bose-Hubbard model. This method well describes the behavior of long-range correlations and therefore is valid deep in the superfluid phase. For the homogeneous Bose-Hubbard model, we draw the finite-temperature phase diagram and calculate the superfluid density at unity filling. We evaluate the finite-temperature effects in a recent experiment probing number fluctuation [Phys. Rev. Lett. \textbf{96}, 090401 (2006)], and find that our finite-temperature curves g…
We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling at a relative low density suppressing the effect of avalanches. With the suppression of avalanches a BEC containing 120.10^6 atoms is produced. The collisional opacity can be tuned from the collisionless regime to a collisional opacity of more than 3 by compressing the trap after condensation. In the collisional opaque regime a significant heating of the cloud at time scales shorter than half of the radial trap period is measured. This is direct pr…
We report on the creation of heterospecies bosonic molecules, associated from an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated magnetic field close to two Feshbach resonances. We measure the binding energy of the weakly bound molecular states versus the Feshbach field and compare our results to theoretical predictions. We observe the broadening and asymmetry of the association spectrum due to thermal distribution of the atoms, and a frequency shift occurring when the binding energy depends nonlinearly on the Feshbach field. A simple model is developed to quantita…
We show that the electron-like and photon-like excitations may exist in a three-dimensional Bose-Fermi Hubbard model describing ultracold Bose-Fermi atom mixtures in optical lattices. In a Mott insulating phase of the Bose atoms, these excitations are stabilized by an induced repulsive interaction between 'electrons' if the Fermi atoms are nearly half filling. We suggest to create 'external electric field' so that the electron-like excitation can be observed by measuring the linear density-density response of the 'electron' gas to the 'external field' in a time-of-flight experiment of the mixt…
We investigate the Bose-Einstein condensation (BEC, superfluidity) of particle-hole pairs in ultracold Fermionic atoms with repulsive interactionsand arbitrary polarization, which are trapped within optical lattices. Near a Feshbach resonance, the dynamics of particle-hole pairs can be described by a hard-core Bose-Hubbard model. The insulator - superfluid and charge-density-wave (CDW) - superfluid phase transitions can be induced by decreasing and increasing the potential depths with controlling the trapping laser intensity, respectively. The parameter and polarization dependence of the criti…
A generalized Fermi-Bose mapping method is used to determine the exact ground states of several models of mixtures of strongly interacting ultracold gases in tight waveguides, which are generalizations of the Tonks-Girardeau (TG) gas (1D Bose gas with point hard cores) and fermionic Tonks-Girardeau (FTG) gas (1D spin-aligned Fermi gas with infinitely strong zero-range attractions). We detail the case of a Bose-Fermi mixture with TG boson-boson (BB) and boson-fermion (BF) interactions. Exact results are given for density profiles in a harmonic trap, single-particle density matrices, momentum di…
A model of two 1D ideal Bose gases A and B with strong AB attractions induced by a p-wave AB Feshbach resonance is studied. The model is solved exactly by a Bose-Bose duality mapping, and it is shown that there is no A-component or B-component Bose-Einstein condensation and no AB-pair off-diagonal long-range order (ODLRO), but both AA-pair and BB-pair ODLRO. After generalization by adding even-wave AA and BB repulsion and reducing the strength of the odd-wave AB attraction by Feshbach resonance detuning, a quantum phase transition occurs between a phase with AB contact nodes and one with no su…
The far-from-equilibrium dynamics of an ultracold, one-dimensional Bose gas is studied. The focus is set on the comparison between the solutions of fully dynamical evolution equations derived from the 2PI effective action and their corresponding kinetic approximation in the form of Boltzmann-type transport equations. It is shown that during the time evolution of the gas a kinetic description which includes non-Markovian memory effects in a gradient expansion becomes valid. The time scale at which this occurs is shown to exceed significantly the time scale at which the system's evolution enters…
We analyze the possibility of a ferroelectric transition in heteronuclear molecules consisting of Bose-Bose, Bose-Fermi or Fermi-Fermi atom pairs. This transition is characterized by the appearance of a spontaneous electric polarization below a critical temperature. We discuss the existence of a ferroelectric Fermi liquid phase for Fermi molecules and the existence of a ferroelectric superfluid phase for Bose molecules characterized by the coexistence of ferroelectric and superfluid orders. Lastly, we propose an experiment to detect ferroelectric correlations through the observation of coheren…
We show that the Calogero-Sutherland (C-S) gas, a famous exact soluble one-dimensional system with an inverse square long range interaction, can be realized by dimension reduction in a cold Bose atom system with a dipole-dipole interaction. Depending on the orientation of the dipoles, the effective interaction is either attractive or repulsive. The low-lying effective theory may be a Luttinger liquid when the exclusion statistics parameter $λ$ may be well-defined. We hope that the C-S gas can be realized experimentally and the Luttinger liquid character can be observed.
We show that the 'electron' and 'photon' can emerge from a supersymmetric Hubbard model which is a non-relativistic theory of the neutral particles. The Higgs boson and 'photon' may not appear in the same phase of the phase diagram. In a Mott insulator phase of the boson, the 'electron' and 'photon' are stablized by an induced Coulomb interaction between 'electrons'. This emergent mechanism may be 'realized' in an ultracold Bose-Fermi atom mixture except the long range Coulomb interaction is repalced by a nearest neighbor one. We suggest to create 'external electric field' so that the 'electro…
We investigate the conditions under which quantum fluctuations are relevant for the quantitative interpretation of experiments with ultracold Bose gases. This requires to go beyond the description in terms of the Gross-Pitaevskii and Hartree-Fock-Bogoliubov mean-field theories, which can be obtained as classical (statistical) field-theory approximations of the quantum many-body problem. We employ functional-integral techniques based on the two-particle irreducible (2PI) effective action. The role of quantum fluctuations is studied within the nonperturbative 2PI 1/N expansion to next-to-leading…
We study quadrupole collective oscillations in the bose-fermi mixtures of ultracold atomic gases of Yb isotopes, which are realized by Kyoto group. Three kinds of combinations are chosen, Yb170-Yb171, Yb170-Yb173 and Yb174-Yb173, where boson-fermion interactions are weakly repulsive, strongly attractive and strongly repulsive respectively. Collective oscillations in these mixtures are calculated in a dynamical time-evolution approach formulated with the time-dependent Gross-Pitaevskii and the Vlasov equations. The boson oscillations are shown to have one collective mode, and the fermions are s…
Mobile impurity atoms immersed in Bose-Einstein condensates provide a new platform for exploring Bose polarons. Recent experimental advances in the field of ultracold atoms make it possible to realize such systems with highly tunable microscopic parameters and to explore equilibrium and dynamical properties of polarons using a rich toolbox of atomic physics. In this paper we present a detailed theoretical analysis of Bose polarons in one dimensional systems of ultracold atoms. By combining a non-perturbative renormalization group approach with numerically exact diffusion Monte Carlo calculatio…
We analyze the dynamics of Bose polarons in the vicinity of a Feshbach resonance between the impurity and host atoms. We compute the radio-frequency absorption spectra for the case when the initial state of the impurity is non-interacting and the final state is strongly interacting. We compare results of different theoretical approaches including a single excitation expansion, a self-consistent T-matrix method, and a time-dependent coherent state approach. Our analysis reveals sharp spectral features arising from metastable states with several Bogoliubov excitations bound to the impurity atom.…
We investigate the dynamics of an effectively one-dimensional Bose-Einstein condensate (BEC) with scattering length $a$ subjected to a spatially periodic modulation, $a=a(x)=a(x+L)$. This "collisionally inhomogeneous" BEC is described by a Gross-Pitaevskii (GP) equation whose nonlinearity coefficient is a periodic function of $x$. We transform this equation into a GP equation with constant coefficient $a$ and an additional effective potential and study a class of extended wave solutions of the transformed equation. For weak underlying inhomogeneity, the effective potential takes a form resembl…
