Jan 2015

Jan 5-Jan 9, Zhenyu Zhou & Jinlong Yu, Jan 12-Jan 16, Jiyao chen & Jianhui zhou, Jan 19-Jan 23, Haiyuan Zou & Ahmet Keles, Jan 26-Jan 30 Zhifang Xu & Xuguang Yue

Jan 30
1.arXiv:1501.07462 [pdf, ps, other]
The anyon Hubbard model in one-dimensional optical lattices
Sebastian Greschner, Luis Santos
Comments: 5 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas)

Raman-assisted hopping may be used to realize the anyon Hubbard model in one-dimensional optical lattices. We propose a feasible scenario that significantly improves the proposal of [T. Keilmann et al., Nature Commun. 2, 361 (2011)], allowing as well for an exact realization of the two-body hard-core constraint, and for controllable effective interactions without the need of Feshbach resonances. We show that the combination of anyonic statistics and two-body hard-core constraint leads to a rich ground-state physics, including Mott-insulators with attractive interactions, pair-superfluids, dimer phases, and multi-critical points. Moreover, the anyonic statistics results in a novel two-component superfluid of holon and doublon dimers, characterized by a large but finite compressibility and a multi-peaked momentum distribution, that may be easily revealed experimentally.

Jan 29
1.arXiv:1501.07004 [pdf, ps, other]
Spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical lattice
Xiaofan Zhou, Kuang Zhang, Junjun Liang, Gang Chen, Suotang Jia
Comments: Submitted to Phys. Rev. A
Subjects: Quantum Gases (cond-mat.quant-gas)

Motivated by recent experimental developments, we investigate spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical lattice. Using exact density-matrix renormalization group method, we calculate the momentum distribution function, the spin-correlation function, and the spin-structure factor to reveal rich ground-state properties. We find that spin-orbit coupling (SOC) can generate unconventional momentum distributions, which depend strongly on the fillings. We call the corresponding phase as the SOC-induced metallic phase. We also show that SOC can drive the system from the antiferromagnetic to the ferromagnetic ground states. As a result, by tuning the on-site repulsive interaction strength, a quantum phase transition between the ferromagnetic Mott insulator and the SOC-induced metallic phase is predicted at the strong SOC. In addition, the momentum, at which peak of the spin-structure factor appears, can be affected dramatically by SOC. The analytical expression of this momentum with respect to the SOC strength is also derived.

Jan 28
1.arXiv:1501.06830 [pdf, other]
Spontaneous PT symmetry breaking of a ferromagnetic superfluid in a gradient field
Thomas Vanderbruggen, Silvana Palacios, Simon Coop, Natali Martinez De Escobar, Mitchell Morgan (ICREA)
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We consider the interaction of a ferromagnetic spinor Bose-Einstein condensate with a magnetic field gradient. The magnetic field gradient realizes a spin-position coupling that explicitly breaks time-reversal symmetry T and space parity P, but preserves the combined PT symmetry. We observe using numerical simulations, a first-order phase transition spontaneously breaking this re-maining symmetry. The transition to a low-gradient phase, in which gradient effects are frozen out by the ferromagnetic interaction, suggests the possibility of high-coherence magnetic sensors unaffected by gradient dephasing.

Jan 27
1.arXiv:1501.05984 [pdf, other]
Itinerant magnetism in spin-orbit coupled Bose gases
D. L. Campbell, R. M. Price, A. Putra, A. Valdés-Curiel, D. Trypogeorgos, I. B. Spielman
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)

Phases of matter are conventionally characterized by order parameters describing the type and degree of order in a system. For example, crystals consist of spatially ordered arrays of atoms, an order that is lost as the crystal melts. Like- wise in ferromagnets, the magnetic moments of the constituent particles align only below the Curie temperature, TC. These two examples reflect two classes of phase transitions: the melting of a crystal is a first-order phase transition (the crystalline order vanishes abruptly) and the onset of magnetism is a second- order phase transition (the magnetization increases continuously from zero as the temperature falls below TC). Such magnetism is robust in systems with localized magnetic particles, and yet rare in model itinerant systems where the particles are free to move about. Here for the first time, we explore the itinerant magnetic phases present in a spin-1 spin-orbit coupled atomic Bose gas; in this system, itinerant ferromagnetic order is stabilized by the spin-orbit coupling, vanishing in its absence. We first located a second-order phase transition that continuously stiffens until, at a tricritical point, it transforms into a first- order transition (with observed width as small as h x 4 Hz). We then studied the long-lived metastable states associated with the first-order transition. These measurements are all in agreement with theory.

Jan 26
1.arXiv:1501.05661 [pdf, other]
Observation of many-body localization of interacting fermions in a quasi-random optical lattice
Michael Schreiber, Sean S. Hodgman, Pranjal Bordia, Henrik P. Lüschen, Mark H. Fischer, Ronen Vosk, Ehud Altman, Ulrich Schneider, Immanuel Bloch
Comments: 6 pages, 6 figures + supplementary information
Subjects: Quantum Gases (cond-mat.quant-gas); Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

We experimentally observe many-body localization of interacting fermions in a one-dimensional quasi-random optical lattice. We identify the many-body localization transition through the relaxation dynamics of an initially-prepared charge density wave. For sufficiently weak disorder the time evolution appears ergodic and thermalizing, erasing all remnants of the initial order. In contrast, above a critical disorder strength a significant portion of the initial ordering persists, thereby serving as an effective order parameter for localization. The stationary density wave order and the critical disorder value show a distinctive dependence on the interaction strength, in agreement with numerical simulations. We connect this dependence to the ubiquitous logarithmic growth of entanglement entropy characterizing the generic many-body localized phase.

Jan 23
arXiv:1501.05320 [pdf, other]
Exotic topological density waves in cold atomic Rydberg fermions
Xiaopeng Li, S. Das Sarma

Comments: 12 pages, 6 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Versatile controllability of interactions in ultracold atomic and molecular gases has now reached an unprecedented era where quantum correlations and unconventional many-body phases can be studied with no corresponding analogs in solid state systems. Recent experiments in Rydberg atomic gases have achieved exquisite control over non-local interactions, allowing novel quantum phases unreachable with the usual local interactions in atomic systems. Here, we study Rydberg dressed atomic fermions in a three dimensional optical lattice predicting the existence of hitherto unheard-of exotic mixed topological density wave phases. We show that varying spatial range of the non-local interaction leads to a rich phase diagram containing various bond density waves, with unexpected spontaneous time-reversal symmetry breaking. Quasiparticles in these chiral phases experience emergent gauge fields and form three dimensional quantum Hall and Weyl semimetal states. Remarkably, certain density waves even exhibit mixed topologies beyond the existing topological classification. Experimental signatures of density waves and their topological properties are predicted in time-of-flight measurements.

Jan 22
arXiv:1501.05015 [pdf, ps, other]
Damping of long wavelength collective modes in spinor Bose-Fermi mixtures
J. H. Pixley, Xiaopeng Li, S. Das Sarma

Comments: 5 pages, 2 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Using an effective field theory we describe the low energy bosonic excitations in a three dimensional ultra-cold mixture of spin-1 bosons and spin-1/2 fermions. We establish an interesting fermionic excitation induced generic damping of the usual undamped long wavelength bosonic collective Goldstone modes. Two states with bosons forming either a ferromagnetic or polar superfluid are studied. The linear dispersion of the bosonic Bogoliubov excitations is preserved with a renormalized sound velocity. For the polar superfluid we find both gapless modes (density and spin) are damped, whereas in the ferromagnetic superfluid we find the density (spin) mode is (not) damped. We argue quite generally that this holds for any mixture of bosons and fermions that are coupled through at least a density-density interaction. We discuss the implications of our many-body interaction results for experiments on Bose-Fermi mixtures.

Jan 21
arXiv:1501.04662 [pdf, other]
Optical generation and detection of pure valley current in monolayer transition metal dichalcogenides
Wen-Yu Shan, Jianhui Zhou, Di Xiao

Journal-ref: Phys. Rev. B 91, 035402 (2015)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We propose a practical scheme to generate a pure valley current in monolayer transition metal dichalcogenides by one-photon absorption of linearly polarized light. We show that the pure valley current can be detected by either photoluminescence measurements or the ultrafast pump-probe technique. Our method, together with the previously demonstrated generation of valley polarization, opens up the exciting possibility of ultrafast optical-only manipulation of the valley index. The tilted field effect on the valley current in experiment is also discussed.

arXiv:1501.04785 [pdf, other]
Quantum Phase Transition of Bosons in a Shaken Optical Lattice
Jiao Miao, Boyang Liu, Wei Zheng

Comments: 11 pages, 7 figures. arXiv admin note: text overlap with arXiv:1402.4569Subjects: Quantum Gases (cond-mat.quant-gas)

Recently, lattice shaking technique has been used to couple different Bloch bands resonantly. For 1D case, in which shaking is along only one direction, experimental observation of effective ferromagnetic domain has been explained by superfluid Ising transition. Inspired by these, we generalize to a 2D case, in which shaking is along two orthogonal directions. Analogy to the 1D case, we find quantum phase transition from normal superfluid(NSF) phase to D4 symmetry breaking superfluid(D4SF) phase. And interaction effect is demonstrated to be responsible for modified critical shaking amplitude. Unlike in the 1D case, here the interaction effect is originated not only in inhomogeneous band mixing in momentum space, but also in different shaking types. We construct a low-energy effective field theory to study the quantum criticality of bosons near the tricritical point separating NSF, D4SF and Mott insulator(MI) phases. Furthermore, we find Bose liquid with anisotropically algebraic order and propose to change Bose-Einstein condensation(BEC) into non-condensed Bose liquid by tuning shaking amplitude approaching the critical value.

Jan 20
arXiv:1501.04369 [pdf, ps, other]
One-dimensional Fermi gas with a single impurity in a harmonic trap: Perturbative description of the upper branch
Seyed Ebrahim Gharashi, X. Y. Yin, Yangqian Yan, D. Blume

Comments: 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas)The transition from "few to many" has recently been probed experimentally in an ultra cold harmonically confined one-dimensional lithium gas, in which a single impurity atom interacts with a background gas consisting of one, two, or more identical fermions [A. N. Wenz {\em{et al.}}, Science {\bf{342}}, 457 (2013)]. For repulsive interactions between the background or majority atoms and the impurity, the interaction energy for relatively moderate system sizes was analyzed and found to converge toward the corresponding expression for an infinitely large Fermi gas. Motivated by these experimental results, we apply perturbative techniques to determine the interaction energy for weak and strong coupling strengths and derive approximate descriptions for the interaction energy for repulsive interactions with varying strength between the impurity and the majority atoms and any number of majority atoms.



Jan 19
arXiv:1501.04086 [pdf, other]
Synthetic gauge fields stabilize a chiral spin liquid phase
Gang Chen, Kaden R. A. Hazzard, Ana Maria Rey, Michael Hermele

Comments: arXiv admin note: text overlap with arXiv:1108.3862Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)We calculate the phase diagram of the SU(N) Hubbard model describing fermionic alkaline earth atoms in a square optical lattice with on-average one atom per site, using a slave-rotor mean-field approximation. We find that the chiral spin liquid predicted for N≥5and large interactions passes through a fractionalized state with a spinon Fermi surface as interactions are decreased before transitioning to a weakly interacting metal. We also show that by adding an artificial uniform magnetic field with flux per plaquette 2π/N, the chiral spin liquid becomes the ground state for all N≥3 at large interactions, persists to weaker interactions, and its spin gap increases, suggesting that the spin liquid physics will persist to higher temperatures. We discuss potential methods to realize the artificial gauge fields and detect the predicted phases.



Jan 16
1. arXiv:1501.03590 [pdf, other]
Evolution of Goldstone mode in binary condensate mixtures
Arko Roy, S. Gautam, D. Angom


We show that the third Goldstone mode in the two-species condensate mixtures, which emerges at phase-separation, gets hardened when the confining potentials have separated trap centers. The {\em sandwich} type condensate density profiles, in this case, acquire a {\em side-by-side} density profile configuration. We use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution and density profiles for these phase transitions at T=0.

2. arXiv:1501.03514 [pdf, other]
Phases of d-orbital bosons in optical lattices
Fernanda Pinheiro, Jani-Petri Martikainen, Jonas Larson


We explore the properties of bosonic atoms loaded into the d bands of an isotropic square optical lattice. Following the recent experimental success reported in [Y. Zhai et al., Phys. Rev. A 87, 063638 (2013)], in which populating d bands with a 99% fidelity was demonstrated, we present a theoretical study of the possible phases that can appear in this system. Using the Gutzwiller ansatz for the three d band orbitals we map the boundaries of the Mott insulating phases. For not too large occupation, two of the orbitals are predominantly occupied, while the third, of a slightly higher energy, remains almost unpopulated. In this regime, in the superfluid phase we find the formation of a vortex lattice, where the vortices come in vortex/anti-vortex pairs with two pairs locked to every site. Due to the orientation of the vortices time-reversal symmetry is spontaneously broken. This state also breaks a discrete Z2-symmetry. We further derive an effective spin-1/2 model that describe the relevant physics of the lowest Mott-phase with unit filling. We argue that the corresponding two dimensional phase diagram should be rich with several different phases. We also explain how to generate antisymmetric spin interactions that can give rise to novel effects like spin canting.

3. arXiv:1501.03495 (cross-list from cond-mat.str-el) [pdf, other]
Constraining quantum critical dynamics: 2+1D Ising model and beyond
William Witczak-Krempa


Quantum critical (QC) phase transitions generally lead to the absence of quasiparticles. The resulting correlated quantum fluid, when thermally excited, displays rich universal dynamics. We establish non-perturbative constraints on the linear-response dynamics of conformal QC systems, in spatial dimensions above one. Specifically, we analyze the large frequency/momentum asymptotics, which we use to derive powerful sum rules. The general results are applied to the O(N) Wilson-Fisher fixed point, describing the QC Ising model when N = 1. We focus on the order parameter and scalar susceptibilities, and the dynamical shear viscosity. Connections to simulations, experiments and interacting gauge theories are made.


 Jan 15

1. arXiv:1501.03269 [pdf, other]
Spatial Patterns of Rydberg Excitations from Logarithmic Pair Interactions
Wolfgang Lechner, Peter ZollerThe collective excitations in ensembles of dissipative, laser driven ultracold atoms exhibit crystal-like patterns, a many-body effect of the Rydberg blockade mechanism. These crystalline structure are revealed in experiment from a post-selection of configurations with fixed numbers of excitations. Here, we show that these sub-ensemble can be well represented by ensembles of effective particles that interact via logarithmic pair potentials. This allows one to study the emergent patterns with a small number of effective particles to determine the phases of Rydberg crystals and to systematically study contributions from N-body terms.




Jan 14

1. arXiv:1501.03095 (cross-list from quant-ph) [pdf, other]
Thermometry Precision in Strongly Correlated Ultracold Lattice Gases
Mohammad Mehboudi, Maria Moreno-Cardoner, Gabriele De Chiara, Anna SanperaThe precise knowledge of the temperature of an ultracold lattice gas simulating a strongly correlated system is a question of both, fundamental and technological importance. Here, we address such question by combining tools from quantum metrology together with the study of the quantum correlations embedded in the system at finite temperatures. Within this frame we examine the spin-1/2 XY chain, first estimating, by means of the quantum Fisher information, the lowest attainable bound on the temperature precision. We then address the estimation of the temperature of the sample from the analysis of correlations using a quantum non demolishing Faraday spectroscopy method. Finally, we demonstrate that for sufficiently low temperatures the proposed measurements are optimal to estimate accurately the temperature of the sample.


Jan 13
1. arXiv:1501.02401 [pdf, ps, other]

Hawking-like escape of the soliton from the trap in two-component Bose-Einstein condensate
Yu. V. Bludov, M. A. García-ÑustesWe demonstrate, that Bose-Einstein condensate can escape from the trap, formed of combined linear periodic (optical lattice) and parabolic potentials, and the escaping mechanism is similar to Hawking radiation from black hole. The low-amplitude bright-bright soliton in two-component Bose-Einstein condensate (where chemical potentials of the BEC first and second components are located nearby the opposite edges of the first band of the optical lattice spectrum) serves as an analogue of particle-antiparticle pair in Hawking radiation. It is shown that parabolic potential, being applied to such two-component BEC, leads to spatial separation of its components: BEC component with chemical potential located in semi-infinite gap exerts the periodical oscillations, while the BEC component, whose chemical potential is in the first finite gap, escapes from the trap (due to negative effective mass of gap soliton). We also propose a method for the creation of such bright-bright soliton -- transferring of atoms from one BEC component to another by spatially periodic linear coupling term.





Jan 9
1.  arXiv:1501.01896 [pdf, other]
`Quantum explosion' of a trapped one-dimensional Bose gas
A. S. Campbell, D. M. Gangardt, K. V. Kheruntsyan
We analyse free expansion of a trapped one-dimensional Bose gas after a sudden release from the confining trap potential. By using the stationary phase and local density approximations, we show that the long-time asymptotic density profile and the momentum distribution of the gas are determined by the initial distribution of Bethe rapidities (quasimomenta) and hence can be obtained from the solutions to the thermodynamic Bethe ansatz equations. For expansion from a harmonic trap, and in the limits of very weak and very strong interactions, we recover the known scaling solutions of the hydrodynamic approach corresponding to self-similar expansion. For all other power-law traps and arbitrary interaction strengths, the expansion is not self-similar and shows strong dependence on the trap anharmonicity of the shape variation of the density profile during evolution. We also characterize dynamical fermionization of an expanding cloud in terms of its first- and second-order coherences describing phase and density fluctuations.

Jan 8
1.  arXiv:1501.01362 [pdf, ps, other]
Superfluidity of pure spin current in ultracold Bose gases
Qizhong Zhu, Qing-feng Sun, Biao Wu
We study the superfluidity of a pure spin current that is a spin current without mass current. We examine two types of pure spin currents, planar and circular, in spin-1 Bose gas. For the planar current, it is usually unstable, but can be stabilized by the quadratic Zeeman effect. The circular current can be generated with spin-orbit coupling. When the spin-orbit coupling strength is weak, we find that the circular pure spin current is the ground state of the system and thus a super-flow. We discuss the experimental schemes to realize and detect a pure spin current.

2. arXiv:1501.01304 [pdf, other]
Competing Chiral Magnetic Orders in the Strongly Correlated Haldane-Hubbard Model
Ciarán Hickey, Pratik Rath, Arun Paramekanti
Motivated by experiments on ultracold atoms which have realized the Haldane model for a Chern insulator, we consider its strongly correlated Mott limit with spin-1/2 fermions. A slave rotor mean field theory suggests the appearance of gapped or gapless chiral spin liquid Mott insulators. To study competing magnetic orders, we consider the strong coupling effective spin Hamiltonian which includes chiral three-spin exchange. We obtain its classical phase diagram, uncovering various chiral magnetic orders including tetrahedral, cone, and noncoplanar spiral states which can compete with putative chiral quantum spin liquids. We study the effect of thermal fluctuations on these states, identifying crossovers in the spin chirality, and phase transitions associated with lattice symmetry breaking. We also discuss analogous effective spin Hamiltonians for correlated spin-1/2 bosons.

Jan 7
1. arXiv:1501.01176 [pdf, ps, other]
Attractive Hofstadter-Hubbard model with imbalanced chemical and vector potentials
M. Iskin

Comments: 11 pages and 12 figures. arXiv admin note: substantial text overlap with arXiv:1406.6890Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

We study the interplay between the Hofstadter butterfly, strong interactions and Zeeman field within the mean-field Bogoliubov-de Gennes theory in real space, and explore the ground states of the attractive single-band Hofstadter-Hubbard Hamiltonian on a square lattice, including the exotic possibility of imbalanced vector potentials. We find that the cooperation between the vector potential and superfluid order breaks the spatial symmetry of the system, and flourish stripe-ordered Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like superfluid and supersolid phases that can be distinguished and characterised according to their coexisting pair-density (PDW), charge-density (CDW) and spin-density (SDW) wave orders. We also discuss confined systems and comment on the likelihood of observing such stripe-ordered phases by loading neutral atomic Fermi gases on laser-induced optical lattices under laser-generated artificial gauge fields.


2. arXiv:1501.01164 [pdf, other]

Spontaneous symmetry breaking in a spin-orbit coupled $f=2$ spinor condensate
Sandeep Gautam, S. K. Adhikari
We study the ground-state density profile of a spin-orbit coupled f=2 spinor condensate in a quasi-one-dimensional trap. The Hamiltonian of the system is invariant under time reversal but not under parity. We identify different parity- and time-reversal-symmetry-breaking states. The time-reversal-symmetry breaking is possible for degenerate states. A phase separation among densities of different components is possible in the domain of time-reversal-symmetry breaking. Different types of parity- and time-reversal-symmetry-breaking states are predicted analytically and studied numerically. We employ numerical and approximate analytic solutions of a mean-field model in this investigation to illustrate our findings.


Jan 6
1. arXiv:1501.00540 [pdf, ps, other]
Unconventional symmetries of Fermi liquid and Cooper pairing properties with electric and magnetic dipolar fermions
Yi Li, Congjun Wu

Comments: Review articleJournal-ref: J. Phys.: Condens. Matter 26, 493203 (2014)Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

The rapid experimental progress of ultra-cold dipolar fermions opens up a whole new opportunity to investigate novel many-body physics of fermions. In this article, we review theoretical studies of the Fermi liquid theory and Cooper pairing instabilities of both electric and magnetic dipolar fermionic systems from the perspective of unconventional symmetries. When the electric dipole moments are aligned by the external electric field, their interactions exhibit the explicit dr2−3z2 anisotropy. The Fermi liquid properties, including the single-particle spectra, thermodynamic susceptibilities, and collective excitations, are all affected by this anisotropy. The electric dipolar interaction provides a mechanism for the unconventional spin triplet Cooper pairing, which is different from the usual spin-fluctuation mechanism in solids and the superfluid 3He. Furthermore, the competition between pairing instabilities in the singlet and triplet channels gives rise to a novel time-reversal symmetry breaking superfluid state. Unlike electric dipole moments which are induced by electric fields and unquantized, magnetic dipole moments are intrinsic proportional to the hyperfine-spin operators with a Lande factor. Its effects even manifest in unpolarized systems exhibiting an isotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi liquid theory supports a collective sound mode exhibiting a topologically non-trivial spin distribution over the Fermi surface. It also leads to a novel p-wave spin triplet Cooper pairing state whose spin and orbital angular momentum are entangled to the total angular momentum J=1 dubbed the J-triplet pairing. This J-triplet pairing phase is different from both the spin-orbit coupled 3He-B phase with J=0and the spin-orbit decoupled 3He-A phase.


Jan 5
1. arXiv:1501.00448 [pdf, ps, other]Fulde-Ferrell superfluids without spin-imbalance in three-dimensional driven spinful fermionic optical latticesZhen Zheng, Chunlei Qu, Xubo Zou, Chuanwei ZhangSpin-imbalanced ultra-cold Fermi gases have been widely studied recently as a platform for exploring the long-sought Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phases, but so far conclusive evidence has not been found. Here we propose to realize an FF superfluid without spin imbalance in a three-dimensional (3D) fermionic cold atom optical lattice, where s- and p-orbital bands of the lattice are coupled by another weak moving optical lattice. Such coupling leads to a spin-independent asymmetric Fermi surface, which, together with the s-wave scattering interaction between two spins, yields an FF type of superfluid pairing. Unlike traditional schemes, our proposal does not rely on the spin imbalance (or an equivalent Zeeman field) to induce the Fermi surface mismatch and may provide a completely new route for realizing FF superfluids.‍

2. arXiv:1501.00425 [pdf, other]Dice lattice and Haldane-like model for quasi-spin-1

T. Andrijauskas, E. Anisimovas, M. Račiūnas, A. Mekys, V. Kudriašov, I. B. Spielman, G. Juzeliūnas
We consider ultracold atoms in a two-dimensional optical lattice of the dice geometry in a tight-binding regime. The atoms experience a laser-assisted tunneling between the nearest neighbour sites of the dice lattice accompanied by the momentum recoil. This allows one to engineer staggered synthetic magnetic fluxes over plaquettes, and thus pave a way towards a realization of topologically nontrivial band structures. In such a lattice the real-valued next-neighbour transitions are not needed to reach a topological regime. Yet, such transitions can increase a variety of the obtained topological phases. The dice lattice represents a triangular Bravais lattice with a three-site basis consisting of a hub site connected to two rim sites. As a consequence, the dice lattice supports three dispersion bands. From this point of view, our model can be interpreted as a generalization of the paradigmatic Haldane model which is reproduced if one of the two rim sub-lattices is eliminated. We demonstrate that the proposed upgrade of the Haldane model creates a significant added value, including an easy access to topological semimetal phases relying only on the nearest neighbour coupling, as well as enhanced topological band structures featuring Chern numbers higher than one. The numerical investigation is supported and complemented by an analytical scheme based on the study of singularities in the Berry connection.‍

3. arXiv:1501.00057 [pdf, other]Seeing spin dynamics in atomic gasesDan M. Stamper-KurnThe dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.

4. arXiv:1501.00228 (cross-list from cond-mat.str-el) [pdf, other]
On the Matrix Product Ansatz for Fermi Fields in One-Dimension
Sangwoo S. Chung, Kuei Sun, C. J. Bolech

Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We present an implementation of a continuous matrix product state for two-component fermions in one-dimension. We propose a construction of variational matrices with an efficient parameterization that respects the translational symmetry of the problem (without being overly constraining) and readily meets the regularity conditions that arise from removing the ultraviolet divergences in the kinetic energy. We test the validity of our approach on an interacting spin-1/2 system and observe that the ansatz correctly predicts the ground state magnetic properties for the attractive spin-1/2 Fermi gas, including the phase-oscillating pair correlation function in the partially polarized regime.