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Quantum Phases of Ultracold Bosonic Atoms in a Two-Dimensional Optical Superlattice  [PDF]
Jing-Min Hou
Physics , 2007,
Abstract: We study quantum phases of ultracold bosonic atoms in a two-dimensional optical superlattice. The extended Bose-Hubbard model derived from the system of ultracold bosonic atoms in an optical superlattice is solved numerically with Gutzwiller approach. We find that the modulated superfluid(MS), Mott-insulator (MI) and density-wave(DW) phases appear in some regimes of parameters. The experimental detection of the first order correlations and the second order correlations of different quantum phases with time-of-flight and noise-correlation techniques is proposed.
Ab-initio phase diagram of ultracold 87-Rb in an one-dimensional two-color superlattice  [PDF]
Felix Schmitt,Markus Hild,Robert Roth
Physics , 2010,
Abstract: We investigate the ab-initio phase diagram of ultracold 87-Rb atoms in an one-dimensional two-color superlattice. Using single-particle band structure calculations we map the experimental setup onto the parameters of the Bose-Hubbard model. This ab-initio ansatz allows us to express the phase diagrams in terms of the experimental control parameters, i.e., the intensities of the lasers that form the optical superlattice. In order to solve the many-body problem for experimental system sizes we adopt the density-matrix renormalization-group algorithm. A detailed study of convergence and finite-size effects for all observables is presented. Our results show that all relevant quantum phases, i.e., superfluid, Mott-insulator, and quasi Bose-glass, can be accessed through intensity variation of the lasers alone. However, it turns out that the phase diagram is strongly affected by the longitudinal trapping potential.
Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical Superlattice  [PDF]
Arya Dhar,Tapan Mishra,Ramesh V. Pai,B. P. Das
Physics , 2011, DOI: 10.1103/PhysRevA.83.053621
Abstract: We analyze various quantum phases of ultracold bosonic atoms in a periodic one dimensional optical superlattice. Our studies have been performed using the finite size density matrix renormalization group (FS-DMRG) method in the framework of the Bose-Hubbard model. Calculations have been carried out for a wide range of densities and the energy shifts due to the superlattice potential. At commensurate fillings, we find the Mott insulator and the superfluid phases as well as Mott insulators induced by the superlattice. At a particular incommensurate density, the system is found to be in the superfluid phase coexisting with density oscillations for a certain range of parameters of the system.
Analytical mean-field approach to the phase-diagram of ultracold bosons in optical superlattices  [PDF]
P. Buonsante,V. Penna,A. Vezzani
Physics , 2004,
Abstract: We report a multiple-site mean-field analysis of the zero-temperature phase diagram for ultracold bosons in realistic optical superlattices. The system of interacting bosons is described by a Bose-Hubbard model whose site-dependent parameters reflect the nontrivial periodicity of the optical superlattice. An analytic approach is formulated based on the analysis of the stability of a fixed-point of the map defined by the self-consistency condition inherent in the mean-field approximation. The experimentally relevant case of the period-2 one-dimensional superlattice is briefly discussed. In particular, it is shown that, for a special choice of the superlattice parameters, the half-filling insulator domain features an unusual loophole shape that the single-site mean-field approach fails to capture.
Correlation Time-of-flight Spectrometry of Ultracold Neutrons  [PDF]
M. I. Novopoltsev,Yu. N. Pokotilovski
Physics , 2010, DOI: 10.1134/S0020441210050039
Abstract: The fearures of the correlation method used in time-of-flight spectrometry of ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy range of ultracold neutrons is described, and results of its testing by measuring spectra of neutrons passing through interference filters are presented.
Stochastic and equilibrium pictures of the ultracold FFR molecular conversion rate  [PDF]
Tomotake Yamakoshi,Shinichi Watanabe,Chen Zhang,Chris H. Greene
Physics , 2013, DOI: 10.1103/PhysRevA.87.053604
Abstract: The ultracold molecular conversion rate occurring in an adiabatic ramp through a Fano-Feshbach resonance is studied and compared in two statistical models. One model, the so-called stochastic phase space sampling (SPSS)[E.Hodby et al., PRL.94 120402(2005)] evaluates the overlap of two atomic distributions in phase space by sampling atomic pairs according to a phase-space criterion. The other model, the chemical equilibrium theory(ChET)[S.Watabe and T.Nikuni, PRA.77 013616(2008)] considers atomic and molecular distributions in the limit of the chemical and thermal equilibrium. The present study applies SPSS and ChET to a prototypical system of K+K K2 in all the symmetry combinations, namely Fermi-Fermi, Bose-Bose, and Bose-Fermi cases. To examine implications of the phase-space criterion for SPSS, the behavior of molecular conversion is analyzed using four distinct geometrical constraints. Our comparison of the results of SPSS with those of ChET shows that while they appear similar in most situations, the two models give rise to rather dissimilar behaviors when the presence of a Bose-Einstein condensate (BEC) strongly affects the molecule formation.
A Thouless Quantum Pump with Ultracold Bosonic Atoms in an Optical Superlattice  [PDF]
Michael Lohse,Christian Schweizer,Oded Zilberberg,Monika Aidelsburger,Immanuel Bloch
Physics , 2015,
Abstract: More than 30 years ago, Thouless introduced the concept of a topological charge pump that would enable the robust transport of charge through an adiabatic cyclic evolution of the underlying Hamiltonian. In contrast to classical transport, the transported charge was shown to be quantized and purely determined by the topology of the pump cycle, making it robust to perturbations. On a fundamental level, the quantized charge transport can be connected to a topological invariant, the Chern number, first introduced in the context of the integer quantum Hall effect. A Thouless quantum pump may therefore be regarded as a 'dynamical' version of the integer quantum Hall effect. Here, we report on the realization of such a topological charge pump using ultracold bosonic atoms that form a Mott insulator in a dynamically controlled optical superlattice potential. By taking in-situ images of the atom cloud, we observe a quantized deflection per pump cycle. We reveal the genuine quantum nature of the pump by showing that, in contrast to ground state particles, a counterintuitive reversed deflection occurs when particles are prepared in the first excited band. Furthermore, we were able to directly demonstrate that the system undergoes a controlled topological phase transition in higher bands when tuning the superlattice parameters.
Magnetic Quantum Phases of Ultracold Dipolar Gases in an Optical Superlattice  [PDF]
Xiangguo Yin,Lushuai Cao,Peter Schmelcher
Physics , 2014,
Abstract: We propose an effective Ising spin chain constructed with dipolar quantum gases confined in a one-dimensional optical superlattice. Mapping the motional degrees of freedom of a single particle in the lattice onto a pseudo-spin results in effective transverse and longitudinal magnetic fields. This effective Ising spin chain exhibits a quantum phase transition from a paramagnetic to a single-kink phase as the dipolar interaction increases. Particularly in the single-kink phase,a magnetic kink arises in the effective spin chain and behaves as a quasi-particle in a pinning potential exerted by the longitudinal magnetic field. Being realizable with current experimental techniques, this effective Ising chain presents a unique platform for emulating the quantum phase transition as well as the magnetic kink effects in the Ising-spin chain and enriches the toolbox for quantum emulation of spin models by ultracold quantum gases.
Cell strong coupling perturbative approach to the phase diagram of ultracold bosons in optical superlattices  [PDF]
Pierfrancesco Buonsante,Alessandro Vezzani
Physics , 2005, DOI: 10.1103/PhysRevA.72.013614
Abstract: The phase diagram of ultracold bosons in realistic optical superlattices is addressed via second-order {\it cell} strong coupling perturbative expansions for the Bose-Hubbard model describing the system. Taking advantage of the cell partition inherent in the complex periodic modulation of a superlattice, this technique allows for the description of the unusual loophole-shaped insulator domains that may occur in the phase diagram of the system, unlike the standard perturbative approach. Furthermore, comparisons with quantum Monte Carlo simulations show that our approach provides quantitatively satisfactory results at a significantly lower computational cost than brute force numerical methods. We explicitly consider the phase diagrams for two realistic 3-periodic optical superlattices. These show that many insulator domains exhibit an unusual reentrant character, which we discuss, and suggest that the quantum phase transition relevant to the loophole-shaped insulating domains does not require extreme experimental condition in order to be observed.
Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional optical superlattice  [PDF]
A. Dhar,D. Rossini,B. P. Das
Physics , 2015, DOI: 10.1103/PhysRevA.92.033610
Abstract: We study the quasiadiabatic dynamics of a one-dimensional system of ultracold bosonic atoms loaded in an optical superlattice. Focusing on a slow linear variation in time of the superlattice potential, the system is driven from a conventional Mott insulator phase to a superlattice-induced Mott insulator, crossing in between a gapless critical superfluid region. Due to the presence of a gapless region, a number of defects depending on the velocity of the quench appear. Our findings suggest a power-law dependence similar to the Kibble-Zurek mechanism for intermediate values of the quench rate. For the temporal ranges of the quench dynamics that we considered, the scaling of defects depends nontrivially on the width of the superfluid region.
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