Jan 2014

Jan 31 | Jan 30 | Jan 29 | Dec 30-Jan 3, Zhengyu Zhou | Jan 1 | Jan 3 | Jan 6-Jan 10, Zhifang Xu | Jan 6 | Jan 7 | Jan 9 | | Jan 10 Jan 27-Jan 31,

Jan 31
1. arXiv:1401.7916 [pdf, other]
Splitting a critical spin chain
Alejandro Zamora, Javier Rodriguez-Laguna, Maciej Lewenstein, Luca Tagliacozzo
We study a quench protocol that conserves the entanglement spectrum of a bipartition of a quantum system. As an example we consider the splitting of a critical Ising chain in two chains, and compare it with the well known case of joining of two chains. We show that both the out of equilibrium time evolution of global properties and the equilibrium regime after the quench of local properties are different in the two scenarios. Since the two quenches only differ in the presence/absence of the conservation of the entanglement spectrum, our results suggest that this conservation plays a fundamental role in both the out-of-equilibrium dynamics and the subsequent equilibration mechanism. We discuss the relevance of our results in the context of quantum simulators.

2. arXiv:1401.7949 [pdf, other]
Measurement of Vacuum Pressure with a Magneto-Optical Trap: a Pressure-Rise Method
Rowan W. G. Moore, Lucie A. Lee, Elizabeth A. Findlay, Lara Torralbo-Campo, Donatella Cassettari
The lifetime of an atom trap is often limited by the presence of residual background gases in the vacuum chamber. This leads to the lifetime being inversely proportional to the pressure. Here we use this dependence to estimate the pressure and to obtain pressure rate-of-rise curves, which are commonly used in vacuum science to evaluate the performance of a system. We observe different rates of pressure increase in response to different levels of outgassing in our system. Therefore we suggest that this is a sensitive method which will be useful in applications of cold atom systems, in particular where the inclusion of a standard vacuum gauge is impractical.

Jan 30
1. arXiv:1401.7608 [pdf, ps, other]
Quantum magnetism of ultracold atoms with a dynamical pseudospin degree of freedom
Tobias Graß, Alessio Celi, Maciej Lewenstein
We consider bosons in a Hubbard lattice with an SU(N) pseudospin degree of freedom which is made dynamical via a coherent transfer term. It is shown that, in the basis which diagonalizes the pseudospin coupling, a generic hopping process affects the spin state, similar to a spin-orbit coupling. This results, for the system in the Mott phase, in a ferromagnetic phase with variable quantization axis. In extreme cases, it can even give rise to antiferromagnetic order.

2. arXiv:1401.7659 [pdf, other]
Making an ultracold gas (review article)
Dylan Jervis, Joseph H. Thywissen
We provide an introduction to the experimental physics of quantum gases. At the low densities of ultracold quantum gases, confinement can be understood from single-particle physics, and interactions can be understood from two-body physics. The structure of atoms provides resonances both in the optical domain and in the radio-frequency domain. Atomic structure data is given for the twenty-seven atomic isotopes that had been brought to quantum degeneracy at the time this chapter was written. We discuss the motivations behind choosing among these species. We review how static and oscillatory fields are treated mathematically. An electric dipole moment can be induced in a neutral atom, and is the basis for optical manipulation as well as short-range interactions. Many atoms have permanent magnetic dipole moments, which can be used for trapping or long-range interactions. The Toronto 40K/87Rb lattice experiment provides an illustration of how these tools are combined to create an ultracold, quantum-degenerate gas.

3. arXiv:1401.7693 [pdf, ps, other]
Josephson physics of spin-orbit coupled elongated Bose-Einstein condensates
M.A. Garcia-March, G. Mazzarella, L. Dell'Anna, B. Juliá-Díaz, L. Salasnich, A. Polls
We consider an ultracold bosonic binary mixture confined in a one-dimensional double-well trap. The two bosonic components are assumed to be two hyperfine internal states of the same atom. We suppose that these two components are spin-orbit coupled between each other. We employ the two-mode approximation starting from two coupled Gross-Pitaevskii equations and derive a system of ordinary differential equations governing the temporal evolution of the inter-well population imbalance of each component and that between the two bosonic species. We study the Josephson oscillations of these spin-orbit coupled Bose-Einstein condensates by analyzing the interplay between the interatomic interactions and the spin-orbit coupling and the self-trapped dynamics of the inter-species imbalance. We show that the dynamics of this latter variable is crucially determined by the relationship between the spin-orbit coupling, the tunneling energy, and the interactions.

4. arXiv:1401.7548 [pdf, ps, other]
Superfluid gas of dipolar chains in multilayer systems in crossed electric and magnetic fields
D. V. Fil, S. I. Shevchenko
Crossed electric and magnetic fields influence dipolar neutral particles in the same way as the magnetic field influences charged particles. The effect of crossed fields is proportional to the dipole moment of particles (inherent or induced). We show that the effect of crossed fields is quite spectacular in a multilayer system of polar molecules with dipole moments perpendicular to the layers. In this system the dipoles are coupled into chains, with a very large dipole moment of a given chain. The crossed fields may then induce a large number of vortices in the superfluid gas of chains. This effect can be used for monitoring the formation and dissociation of chains in multilayer dipolar structures.

Jan 29
1. arXiv:1401.7343 [pdf, other]
Majorana edge modes protected by emergent symmetry in a one dimensional fermi gas
Jonathan Ruhman, Ehud Altman
We show that a one dimensional ultra-cold Fermi gas with Rashba-like spin orbit coupling, a Zeeman field and intrinsic attractive interactions exhibits a novel topological superfluid state, which forms in spite of total number conservation and the absence of a single particle gap. Majorana zero modes are localized to the interface between a topological region in the middle of the trap and trivial regions at its wings. Unlike the realization of a topological superconductor in proximity coupled nano-wires, the Majorana modes do not carry a quantum number associated with the total fermion parity. Instead, the topological degeneracy is protected by an emergent Z2 symmetry present only at low energies. We discuss the experimental implications of the novel zero modes, as manifest for example in the response to modulation of a local potential near the position of the Majorana bound states. For the range of interaction strength corresponding to Luttinger parameter 1<K<2 the zero modes are unseperable from the gapless phonon continuum and therefore show up as an algebraic zero bias resonance in the response. For K>2, on the other hand the zero-mode can be detected as a sharp low frequency response at an energy which generically scales with system size as 1/LK/2 and is therefore parametrically separated from the phonons.

Jan 28
1. arXiv:1401.6949 [pdf, ps, other]
Imprinting a topological interface using Zeeman shifts in an atomic spinor Bose-Einstein condensate
Magnus O. Borgh, Justin Lovegrove, Janne Ruostekoski
We propose to use spatial control of the Zeeman energy shifts in an ultracold atomic gas to engineer an interface between topologically distinct regions. This provides an experimentally accessible means for studying the interface physics of topological defects and textures. Using the spin-1 Bose-Einstein condensate as an example, we find spinor wave functions that represent defects and textures continuously connecting across the interface between polar and ferromagnetic regions induced by spatially varying Zeeman shifts. By numerical energy minimization we characterize the defect core structures and determine the energetic stability. The techniques proposed could potentially be used in the laboratory to emulate complex interface physics arising, e.g., in cosmological and condensed-matter contexts in both uniform and lattice systems.

Jan 27
1. arXiv:1401.6648 [pdf, ps, other]
Particle-Hole Pair Coherence in Mott Insulator Quench Dynamics
K. W. Mahmud, L. Jiang, P. R. Johnson, E. Tiesinga
We predict the existence of novel collapse and revival oscillations that are a distinctive signature of the short-range off-diagonal coherence associated with particle-hole pairs in Mott insulator states. Starting with an atomic Mott state in a one-dimensional optical lattice, suddenly raising the lattice depth freezes the particle-hole pairs in place and induces phase oscillations. The peak of the quasi-momentum distribution, revealed through time of flight interference, oscillates between a maximum occupation at zero quasi-momentum (the Γ point) and the edge of the Brillouin zone. We show that the population enhancements at the edge of the Brillouin zone is due to coherent particle-hole pairs, and we find similar effects for fermions and Bose-Fermi mixtures in a lattice. Our results open a new avenue for probing strongly correlated many-body states with short-range phase coherence that goes beyond the familiar collapse and revivals previously observed in the long-range coherent superfluid regime.

2. arXiv:1401.6414 [pdf, ps, other]
Trapped-ion quantum simulation of tunable-range Heisenberg chains
Tobias Graß, Maciej Lewenstein
Quantum-optical techniques allow for generating controllable spin-spin interactions between ions, making trapped ions an ideal quantum simulator of Heisenberg chains. A single parameter, the detuning of the Raman coupling, allows to switch between ferromagnetic and antiferromagnetic chains, and to modify the range of the interactions. On the antiferromagnetic side, the system can be tuned from an extreme long-range limit, in which any pair of ions interacts with almost equal strength, to interactions with a 1/r3 decay. By exact diagonalization, we study how a system of up to 20 ions behaves upon tuning the interactions. We find that it undergoes a transition from a dimerized state with extremely short-ranged correlations towards a state with quasi long-range order, that is, algebraically decaying correlations. On the ferromagnetic side of the system, we demonstrate the feasibility of witnessing non-locality of quantum correlations.

Jan 13-Jan 17, Bo Liu


Jan 17

1.arXiv:1401.4041 [pdf, other]
Quantum Analogs of Classical Wakes in Bose-Einstein Condensates
G. W. Stagg, N. G. Parker, C. F. Barenghi
We show that an elliptical obstacle moving through a Bose-Einstein condensate generates wakes of quantum vortices which resemble those of classical viscous flow past a cylinder or sphere. The role of ellipticity is to facilitate the interaction of the vortices nucleated by the obstacle. Initial steady symmetric wakes lose their symmetry and form clusters of like-signed vortices, in analogy to the classical B\'enard-von K\'arm\'an vortex street. Our findings, demonstrated numerically in both two and three dimensions, confirm the intuition that a sufficiently large number of quanta of circulation reproduce classical physics.

2.arXiv:1401.3777 [pdf, ps, other]
Dark Solitons with Majorana Fermions in Spin-Orbit-Coupled Fermi Gases
Yong Xu, Li Mao, Biao Wu, Chuanwei Zhang
Solitons, which maintain their solitary wavepacket shape while traveling, are crucially important in many physical branches. Recently, dark solitons have been experimentally observed in spin-balanced ultra-cold degenerate Fermi gases. Here we show that a single dark soliton can also exist in a spin-orbit-coupled Fermi gas with a high spin imbalance, where spin-orbit coupling favors uniform superfluids over non-uniform Fulde-Ferrell-Larkin-Ovchinnikov states, leading to dark soliton excitations in highly imbalanced gases. Above a critical spin imbalance, two topological Majorana fermions (MFs) without interactions can coexist inside a dark soliton, paving a way for manipulating MFs through controlling solitons. At the topological transition point, the atom density contrast across the soliton suddenly vanishes, suggesting a signature for identifying topological solitons.

Jan 16

1.arXiv:1401.3514 [pdf, ps, other]
Universal quantum behaviors of interacting fermions in 1D traps: from few particles to the trap thermodynamic limit
Adriano Angelone, Massimo Campostrini, Ettore Vicari
We investigate the ground-state properties of trapped fermion systems described by the Hubbard model with an external confining potential. We discuss the universal behaviors of systems in different regimes: from few particles, i.e. in dilute regime, to the trap thermodynamic limit. 
The asymptotic trap-size (TS) dependence in the dilute regime (increasing the trap size l keeping the particle number N fixed) is described by a universal TS scaling controlled by the dilute fixed point associated with the metal-to-vacuum quantum transition. This scaling behavior is numerically checked by DMRG simulations of the one-dimensional (1D) Hubbard model. In particular, the particle density and its correlations show crossovers among different regimes: for strongly repulsive interactions they approach those of a spinless Fermi gas, for weak interactions those of a free Fermi gas, and for strongly attractive interactions they match those of a gas of hard-core bosonic molecules. 
The large-N behavior of systems at fixed N/l corresponds to a 1D trap thermodynamic limit. We address issues related to the accuracy of the local density approximation (LDA). We show that the particle density approaches its LDA in the large-l limit. When the trapped system is in the metallic phase, corrections at finite l are O(l^{-1}) and oscillating around the center of the trap. They become significantly larger at the boundary of the fermion cloud, where they get suppressed as O(l^{-1/3}) only. This anomalous behavior arises from the nontrivial scaling at the metal-to-vacuum transition occurring at the boundaries of the fermion cloud.



Jan 15

1. arXiv:1401.3179 [pdf, ps, other]
A tight binding model for quantum spin Hall effect on triangular optical lattice
Ahad K. Ardabili, Tekin Dereli, Özgür E. Müstecaplıoğlu
We propose a tight binding model for the quantum spin Hall system on triangular optical lattice and we determined the edge state spectrum which contains gap traversing states as the hallmark of $\mathds{Z}_{2}$ topological insulator. The advantage of this system is the possibility of implementing it in the fermionic ultracold atomic system whose nearly free electron limit is proposed by B. B\'eri and N. R. Cooper, Phys. Rev. Lett. {\bf 107}, 145301 (2011).


Jan 14

1. arXiv:1401.2961 [pdf, ps, other]Polarons in a Dipolar Condensate
Ben Kain, Hong Y. Ling
We consider a polaronic model in which impurity fermions interact with background bosons in a dipolar condensate. The polaron in this model emerges as an impurity dressed with a cloud of phonons of the dipolar condensate, which, due to the competition between the attractive and repulsive part of the dipole-dipole interaction, obey an anisotropic dispersion spectrum. We study how this anisotropy affects the Cerenkov-like emission of Bogoliubov phonon modes, which can be directly verified by experiments in which a dipolar BEC moves against an obstacle. We also study the spectral function of impurity fermions, which is directly accessible to the momentum resolved rf spectroscopy in cold atoms.

2. arXiv:1401.2535 [pdf, ps, other]
Quantum dynamics and entanglement in coherent transport of atomic population
M.K. Olsen
In this work we look at the quantum dynamics of the process known as either transport without transit (TWT), or coherent transfer of atomic population (CTAP), of a Bose-Einstein condensate from one well of a lattice potential to another, non-adjacent well, without macroscopic occupation of the well between the two. This process has previously been analysed and in this work we extend those analyses by considering the effects of quantum statistics on the dynamics and entanglement properties of the condensate modes in the two relevant wells. In order to do this, we go beyond the mean-field analysis of the Gross-Pitaevskii type approach and utilise the phase-space stochastic methods so well known in quantum optics. In particular, we use the exact positive-P representation where it is suitable, and the approximate truncated WIgner representation otherwise. We find strong agreement between the results of these two methods, with the mean-field dynamics not depending on the initial quantum states of the trapped condensate. We find that the entanglement properties do depend strongly on the initial quantum states, with quantitatively different results found for coherent and Fock states. Comparison of the two methods gives us confidence that the truncated Wigner representation delivers accurate results for this system and is thus a useful method as the collisional nonlinearity increases and the positive-P results fail to converge.

Jan 13
1.arXiv:1401.2390 [pdf, ps, other]
Nonequilibrium States of a Quenched Bose Gas
Ben Kain, Hong Y. Ling
Yin and Radzihovsky [1] recently developed a self-consistent extension of a Bogoliubov theory, in which the condensate number density nc is treated as a mean field that changes with time, in order to analyze a JILA experiment by Makotyn et al. [2] on a 85Rb Bose gas following a deep quench to a large scattering length. We apply this theory to construct a set of closed equations that highlight the role of n˙c, which is to induce an effective interaction between quasiparticles. We show analytically that such a system supports a steady state characterized by a constant condensate density and a steady but periodically changing momentum distribution, whose time average is described exactly by the generalized Gibbs ensemble. We discuss how the n˙c-induced effective interaction, which cannot be ignored on the grounds of the adiabatic approximation for modes near the gapless Goldstone mode, can affect experimentally mensurable quantities such as Tan's contact.


2. arXiv:1401.2237 [pdf, other]
Quantum hexatic order in two-dimensional dipolar and charged fluids
Georg M. Bruun, David R. Nelson
Recent advances in cold atom experimentation suggest that studies of quantum two-dimensional melting of dipolar molecules, with dipoles aligned perpendicular to ordering plane, may be on the horizon. An intriguing aspect of this problem is that two-dimensional \emph{classical} aligned dipoles (already studied in great detail in soft matter experiments on magnetic colloids) are known to melt via a two-stage process, with an intermediate hexatic phase separating the usual crystal and isotropic fluid phases. We estimate here the effect of quantum fluctuations on this hexatic phase, for both dipolar systems and charged Wigner crystals. Our approximate phase diagrams rely on a pair of Lindemann criteria, suitably adapted to deal with effects of thermal fluctuations in two dimensions. As part of our analysis, we determine the phonon spectra of quantum particles on a triangular lattice interacting with repulsive 1/r3 and 1/r potentials. A large softening of the transverse and longitudinal phonon frequencies, due to both lattice effects and quantum fluctuations, plays a significant role in our analysis. The hexatic phase is predicted to survive down to very low temperatures.



Dec 30-Jan 3, Zhengyu Zhou
Jan 1
arXiv:1401.0241
Quantum phases in p-orbital degenerated attractive 1D fermionic optical lattices
Keita Kobayashi, Yukihiro Ota, Masahiko Okumura, Susumu Yamada, Masahiko Machida
Subjects: Quantum Gases (cond-mat.quant-gas)

We examine quantum phases emerged by double degeneracy of p-orbital bands in attractive atomic Fermi gases loaded on a 1D optical lattice. Our numerical simulations by the density-matrix renormalization group predict the emergence of a state with a charge excitation gap, the Haldane insulator phase. A mapping onto an effective spin-1 model reveals its physical origin. Moreover, we show that population imbalance leads to richer diversity of the quantum phases, including a phase-separated polarized state. Finally, we show that the Haldane phases and the polarized states can be detected, via the measurements of the population density profiles in harmonic trap potential.

Jan 2
arXiv:1401.0527
Superfluid-Mott insulator transition in spin-orbit coupled Bose-Hubbard Model
A. T. Bolukbasi, M. Iski
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We consider a square optical lattice in two dimensions and study the effects of both the strength and symmetry of spin-orbit-coupling (SOC) and Zeeman field on the ground-state, i.e., Mott insulator (MI) and superfluid (SF), phases and phase diagram, i.e., MI-SF phase transition boundary, of the two-component Bose-Hubbard model. In particular, based on a variational Gutzwiller ansatz, our numerical calculations show that the spin-orbit coupled SF phase is a nonuniform (twisted) one with its phase (but not the magnitude) of the order parameter modulating from site to site. Fully analytical insights into the numerical results are also given.


Jan 3
1. arXiv:1401.0593 [pdf, other]
Spin Liquid Condensate of Spinful Bosons
Biao Lian, Shou-Cheng Zhang
Comments: 5+3 pages
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We introduce the concept of a bosonic spin liquid condensate (SLC), where spinful bosons in a lattice form a Bose-Einstein condensate (BEC) which is a total spin singlet and does not break the spin rotation symmetry. It has an energy gap to all spin excitations. The realization of this SLC requires the spin of the bosons to be S≥2. We give the phase diagram for the spin 2 case using a variational wave function method, and verify the existence of an SLC phase. We show there is a direct analogy between SLC and the resonating-valence-bond (RVB) state.

2. arXiv:1401.0735 [pdf, ps, other]
Dynamics of correlations in a quasi-2D dipolar Bose gas following a quantum quench
Stefan S. Natu, L. Campanello, S. Das Sarma
Comments: 6 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We study the evolution of correlations in a quasi-2D dipolar gas driven out-of-equilibrium by a sudden ramp of the interaction strength. For sufficiently strong ramps, the momentum distribution, excited fraction and density-density correlation function all display pronounced features that are directly related to the appearance of a roton minimum in the underlying spectrum. Our study suggests that the evolution of correlations following a quench can be used as a probe of roton-like excitations in a dipolar gas. We also find that the build up of density-density correlations following a quench occurs much more slowly in the dipolar gas compared to a non-dipolar gas, owing to the long-range interactions.

Jan 6-Jan 10, Zhifang Xu

Jan 6
1.arXiv:1401.0593 [pdf, other]
Spin Liquid Condensate of Spinful Bosons
Biao Lian, Shou-Cheng Zhang
Comments: 5+3 pages
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We introduce the concept of a bosonic spin liquid condensate (SLC), where spinful bosons in a lattice form a Bose-Einstein condensate (BEC) which is a total spin singlet and does not break the spin rotation symmetry. It has an energy gap to all spin excitations. The realization of this SLC requires the spin of the bosons to be S\ge2. We give the phase diagram for the spin 2 case using a variational wave function method, and verify the existence of an SLC phase. We show there is a direct analogy between SLC and the resonating-valence-bond (RVB) state.

2.arXiv:1401.0575 [pdf, ps, other]
Spin-Orbit Coupled Bose Gases at Finite Temperatures
Renyuan Liao, Oleksandr Fialko
Comments: 5 pages, 2 figures
Subjects: Quantum Gases (cond-mat.quant-gas)

Spin-orbit coupling is predicted to have dramatic effects on thermal properties of a two-component atomic Bose gas. We show that in three spatial dimensions it lowers the critical temperature of condensation and enhances thermal depletion of the condensate fraction. In two dimensions we show that spin-orbit coupling destroys superfluidity at any finite temperature, modifying dramatically the cerebrated Berezinskii-Kosterlitz-Thouless scenario. We explain this by the increase of the number of low energy states induced by spin-orbit coupling, enhancing the role of quantum fluctuations.

Jan 7
1.arXiv:1401.0965 [pdf, other]
Three Identical Fermions with Resonant p-wave Interactions in Two Dimensions
Chao Gao, Zhenhua Yu
Comments: 5 pages, 1 figure
Subjects: Quantum Gases (cond-mat.quant-gas)

A new kind of "super-Efimov" states of binding energies scaling as \ln|E_n|\sim-e^{3n\pi/4} were predicted by a field theory calculation for three fermions with resonant p-wave interactions in two dimensions [Phys. Rev. Lett. \textbf{110}, 235301 (2013)]. However, the universality of these "super-Efimov" states has not been proved independently. In this Letter, we study the three fermion system through the hyperspherical formalism. Within the adiabatic approximation, we find that at p-wave resonances, the low energy physics of states of angular momentum \ell=\pm1 crucially depends on the value of an emergent dimensionless parameter Y determined by the detail of the inter-particle potential. Only if Y is exactly zero, the predicted "super-Efimov" states exist. If Y>0, the scaling of the bound states changes to \ln|E_n|\sim-(n\pi)^2/2Y, while there are no shallow bound states if Y<0.

2.arXiv:1401.0952 [pdf, other]
Radio frequency spectroscopy of polarons in ultracold Bose gases
Aditya Shashi, Fabian Grusdt, Dmitry A. Abanin, Eugene Demler
Comments: 18 pages, including 7 figures and 2 Appendices
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Recent experimental advances enabled the realization of mobile impurities immersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here we consider impurities with two or more internal hyperfine states, and study their radio-frequency (RF) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate RF spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is non-interacting, by performing a non-perturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The RF signal contains a delta-function peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The RF spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic power-law tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct RF measurement, in which the impurity is initially in an interacting state, and the inverse RF measurement, in which the impurity is initially in a non-interacting state. In the latter case, in order to calculate the RF spectrum, we solve the problem of polaron formation: a mobile impurity dynamically gets dressed by Bogoliubov phonons. Our solution based on a time-dependent variational ansatz of coherent states of Bogoliubov phonons, becomes exact when the impurity is localized. Moreover we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states interact with the BEC.

Jan 9
1.arXiv:1401.1718 [pdf, other]
Design of laser-coupled honeycomb optical lattices supporting Chern insulators
E. Anisimovas, F. Gerbier, T. Andrijauskas, N. Goldman
Comments: 9 pages, 7 figures; Submitted to Phys. Rev. A
Subjects: Quantum Gases (cond-mat.quant-gas)

We introduce an explicit scheme to realize Chern insulating phases employing cold atoms trapped in a state-dependent optical lattice and laser-induced tunneling processes. The scheme uses two internal states, a ground state and a long-lived excited state, respectively trapped in separate triangular and honeycomb optical lattices. A resonant laser coherently coupling the two internal states enables hopping between the two sublattices with a Peierls-like phase factor. Although laser-induced hopping by itself does not lead to topological bands with non-zero Chern numbers, we find that such bands emerge when adding an auxiliary lattice that perturbs the lattice structure, effectively turning it at low energies into a realization of the Haldane model: A two-dimensional honeycomb lattice breaking time-reversal symmetry. We investigate the parameters of the resulting tight-binding model using first-principles band structure calculations to estimate the relevant regimes for experimental implementation.

2. arXiv:1401.1586 [pdf, ps, other]
Strongly fluctuating fermionic superuid in attractive pi-flux Hubbard model
Ya-Jie Wu, Jiang Zhou, Su-Peng Kou
Comments: 11 pages, 8 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

Ultracold atoms in optical lattice provides a platform to realize the superfluid (SF) state, a quantum order with paired charge-neutral fermions. In this paper, we studied SF state in the twodimensional attractive Hubbard model with pi-flux on each plaquette. The SF state in the pi-flux lattice model suffers very strong quantum fluctuations and the ground state becomes a possible quantum phase liquid state. In this phase, there exists the Cooper pairing together with a finite energy gap for the atoms, but no long range SF phase coherence exists at zero temperature. In addition, we discussed the properties of the SF vortices.

3.arXiv:1401.1704 (cross-list from nlin.AO) [pdf, other]
Spatiotemporal Oscillation Patterns in the Collective Relaxation Dynamics of Interacting Particles in Periodic Potentials
Benno Liebchen, Peter Schmelcher
Subjects: Adaptation and Self-Organizing Systems (nlin.AO); Other Condensed Matter (cond-mat.other)

We demonstrate the emergence of self-organized structures in the course of the relaxation of an initially excited, dissipative and finite chain of interacting particles in a periodic potential towards its many particle equilibrium configuration. Specifically we observe a transition from an in phase correlated motion via phase randomized oscillations towards oscillations with a phase difference $\pi$ between adjacent particles thereby yielding the growth of long time transient spatiotemporal oscillation patterns. Parameter modifications allow for designing these patterns, including steady states and even states that combine in phase and correlated out of phase oscillations along the chain. The complex relaxation dynamics is based on finite size effects together with an evolution running from the nonlinear to the linear regime thereby providing a highly unbalanced population of the center of mass and relative motion.
Jan 10
1.arXiv:1401.1986 [pdf, other]
Quantum Quench and Prethermalization Dynamics in A Two-Dimensional Fermi Gas with Long-range Interactions
N. Nessi, A. Iucci, M. A. Cazalilla
Comments: 9 pages, 2 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)

We study the effect of suddenly turning on a long-range interaction in a spinless Fermi gas in two dimensions. The short to intermediate time dynamics is obtained using the method of bosonization of the Fermi surface. This allow to calculate the full space-time dependence of the non-equilibrium fermion density matrix as well as the evolution of the quasiparticle residue after the quench. It is thus found that the asymptotic state predicted by bosonization is consistent with the prethermalized state. From the bosonized representation, we explicitly construct the Generalized Gibbs Ensamble that describes the prethermalized state. A protocol to perform an interaction quantum quench in a dipolar gas of Erbium atoms is also described.

2.arXiv:1401.1961 [pdf, ps, other]
On the effective Dirac equation for ultracold atoms in optical lattices: role of the localization properties of the Wannier functions
Xabier Lopez-Gonzalez, Jacopo Sisti, Giulio Pettini, Michele Modugno
Comments: 6 pages, 5 figures
Subjects: Quantum Gases (cond-mat.quant-gas); High Energy Physics - Phenomenology (hep-ph)

We review the derivation of the effective Dirac equation for ultracold atoms in one-dimensional bichromatic optical lattices, following the proposal by Witthaut et al. Phys. Rev. A 84, 033601 (2011). We discuss how such a derivation - based on a suitable rotation of the Bloch basis and on a coarse graining approximation - is affected by the choice of the Wannier functions entering the coarsening procedure. We show that in general the Wannier functions obtained by rotating the maximally localized Wannier functions for the original Bloch bands can be sufficiently localized for justifying the coarse graining approximation. We also comment on the relation between the rotation needed to achieve the Dirac form and the standard Foldy-Wouthuysen transformation. Our results provide a solid ground for the interpretation of the experimental results by Salger et al. Phys. Rev. Lett. 107, 240401 (2011) in terms of an effective Dirac dynamics.

3.arXiv:1401.1823 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
Tri-Dirac Surface Modes in Topological Superconductors
Chen Fang, B. Andrei Bernevig, Matthew J. Gilbert
Comments: Five-page main text plus five-page supplementary materials; three figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)

We propose a new type of topological surface modes having cubic dispersion in three-dimensional topological superconductors. Lower order dispersions are prohibited by the threefold rotational symmetry and time-reversal symmetry. Cooper pairing in the bulk changes sign under improper rotations, akin to^{3}He-B. The surface manifestations are a divergent surface density of states at the Fermi level and isospins that rotate three times as they circle the origin in momentum space. We propose that Heusler alloys with band inversion are candidate materials to harbor the novel topological superconductivity.