Aug+2014

flat =Aug 4-Aug 8, Zhenyu zhou & Jinlong Yu, Aug 11-Aug 15, Jiyao chen & Jianhui zhou, Aug 18-Aug 22, Haiyuan Zou & Ahmet Keles, Aug 25-Aug 29, Zhifang Xu & Xuguang Yue=

=Aug29= 1. [|arXiv:1408.6743] [[|pdf], [|other]] Quench dynamics and statistics of measurements for a line of quantum spins in two dimensions [|Jonathan Lux], [|Achim Rosch] Comments: 10 pages, 7 figures Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Motivated by recent experiments, we investigate the dynamics of a line of spin-down spins embedded in the ferromagnetic spin-up ground state of a two-dimensional xxz model close to the Ising limit. In a situation where the couplings in x and y direction are different, the quench dynamics of this system is governed by the interplay of one-dimensional excitations (kinks and holes) moving along the line and single-spin excitations evaporating into the two-dimensional background. A semiclassical approximation can be used to calculate the dynamics of this complex quantum system. Recently, it became possible to perform projective quantum measurements on such spin systems, allowing to determine, e.g., the z-component of each individual spin. We predict the statistical properties of such measurements which contain much more information than correlation functions.

2. [|arXiv:1408.6582] [[|pdf], [|ps], [|other]] Pairing symmetry of superfluid state in three-component repulsive fermionic atoms in optical lattices [|Kensuke Inaba], [|Sei-ichiro Suga] Comments: 5 pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas)

We investigate the pairing symmetry of the superfluid state in repulsively interacting three-component (colors) fermionic atoms in optical lattices. When two of the three color-dependent repulsions are much larger than the other, pairing symmetry is an extended s wave although the superfluid state appears adjacent to the paired Mott insulator in the phase diagram. As the difference between the three repulsions is decreased in square optical lattices, the extended s-wave pairing changes into a nodal s-wave pairing and then into a d-wave pairing. This change in pairing symmetry is attributed to the competition among the density fluctuations of unpaired atoms, the quantum fluctuations of the color-density wave, and those of the color-selective antiferromagnet. This phenomenon can be studied using existing experimental techniques.

3. [|arXiv:1408.6830] (cross-list from quant-ph) [[|pdf], [|other]] Dissipative phase transitions: independent vs. collective decay and spin squeezing [|Tony E. Lee], [|Ching-Kit Chan], [|Susanne F. Yelin] Comments: 9 pages, 6 figures Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Chaotic Dynamics (nlin.CD)

We study the XY model with infinite-range interactions (Lipkin-Meshkov-Glick model) in the presence of dissipation from spontaneous decay. We show that independent and collective decay lead to qualitatively different phase transitions of the steady state, even though the phase boundary is the same. Independent decay leads to a second-order phase transition to a ferromagnet, while collective decay leads to a first-order transition to a time-dependent oscillatory phase. Then we show that the addition of a drive leads to infinite spin squeezing for collective decay in the thermodynamic limit. The combination of spin-spin interaction and drive leads to more spin squeezing than each by itself. Our results can be experimentally seen in trapped-ion and cavity-QED experiments.

4. [|arXiv:1408.6820] [[|pdf], [|other]] Emergence of $p+ip$ superconductivity in $2$D strongly correlated Dirac fermions [|Zheng-Cheng Gu], [|Hong-Chen Jiang], [|G. Baskaran] Comments: 7 pages, 5 figures Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)

Searching for p+ip superconducting(SC) state has become a fascinating subject in condensed matter physics, as a dream application awaiting in topological quantum computation. In this paper, we report a theoretical discovery of a p+ip SC ground state (coexisting with ferromagnetic order) in honeycomb lattice Hubbard model with infinite repulsive interaction at low doping(δ<0.2), by using both the state-of-art Grassmann tensor product state(GTPS) approach and a quantum field theory approach. Our discovery suggests a new mechanism for p+ipSC state in generic strongly correlated systems and opens a new door towards experimental realization. The p+ip SC state has an instability towards a potential non-Fermi liquid with a large but finite U. However, a small Zeeman field term stabilizes the p+ip SC state. Relevant realistic materials are also proposed.

=Aug 28= 1. [|arXiv:1408.6377] [[|pdf], [|other]] Ultracold atoms out of equilibrium [|Tim Langen], [|Remi Geiger], [|Jörg Schmiedmayer] Comments: Comments welcome Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)

The relaxation of isolated quantum many-body systems is a major unsolved problem connecting statistical and quantum physics. Studying such relaxation processes remains a challenge despite considerable efforts. Experimentally, it requires the creation and manipulation of well-controlled and truly isolated quantum systems. In this context, ultracold neutral atoms provide unique opportunities to understand non-equilibrium phenomena because of the large set of available methods to isolate, manipulate and probe these systems. Here, we give an overview of the rapid experimental progress that has been made in the field over the last years and highlight some of the questions which may be explored in the future.

2. [|arXiv:1408.6419] [[|pdf], [|other]] Quasi-particle Lifetime in a Mixture of Bose and Fermi Superfluids [|Wei Zheng], [|Hui Zhai] Comments: 8 pages and 3 figures including supplemental material Subjects: Quantum Gases (cond-mat.quant-gas)

In this letter, to reveal the effect of quasi-particle interactions in a Bose-Fermi superfluid mixture, we consider the lifetime of quasi-particle of Bose superfluid due to its interaction with quasi-particles in Fermi superfluid. We find that this damping rate, i.e. inverse of the lifetime, has quite different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant nearby the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because in the BCS side the decay processe is restricted by constant density-of-state of fermion quasi-particle nearby Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasi-particles of Fermi superfluid. Our results are related to collective mode experiment in recently realized Bose-Fermi superfluid mixture.

3. [|arXiv:1408.6421] [[|pdf], [|other]] A Two-dimensional Algebraic Quantum Liquid Produced by an Atomic Simulator of the Quantum Lifshitz Model[| Hoi Chun Po], [|Qi Zhou] Comments: 3 figures Subjects: Quantum Gases (cond-mat.quant-gas)

Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonian are required for suppressing the condensation. Here, we show that ultra cold atoms with synthetic spin-orbit coupling provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where the single-particle ground state shrinks to a point from a circle in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.

=Aug 27= 1. [|arXiv:1408.6058] [[|pdf], [|ps], [|other]] Hyperspherical Treatment of Strongly-Interacting Few-Fermion Systems in One Dimension [|A. G. Volosniev], [|D. V. Fedorov], [|A. S. Jensen], [|N. T. Zinner] Comments: 5 pages. Original paper for EPJ ST in connection with the workshop BEC2014 28-31 May 2014 in Levico Terme, Italy Subjects: Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph)

We examine a one-dimensional two-component fermionic system in a trap, assuming that all particles have the same mass and interact through a strong repulsive zero-range force. First we show how a simple system of three strongly interacting particles in a harmonic trap can be treated using the hyperspherical formalism. Next we discuss the behavior of the energy for the N-body system.

2. [|arXiv:1408.5913] [[|pdf], [|ps], [|other]] Sound-induced vortex interactions in a zero temperature two-dimensional superfluid [|Andrew Lucas], [|Piotr Surówka] Comments: 20 pages Subjects: Quantum Gases (cond-mat.quant-gas) ; High Energy Physics - Theory (hep-th)

We present a systematic derivation of the effective action for interacting vortices in a non-relativistic two-dimensional superfluid described by the Gross-Pitaevskii equation by integrating out longitudinal fluctuations of the order parameter. There are no logarithmically divergent coefficients in the equations of motion. Our analysis is valid in a dilute limit of vortices where the intervortex spacing is large compared to the core size, and where number fluctuations of atoms in vortex cores are suppressed. We analyze sound-induced corrections to the dynamics of a vortex-antivortex pair and show that there is no instability to annihilation, suggesting that sound-mediated interactions are not strong enough to ruin an inverse energy cascade in two-dimensional zero temperature superfluid turbulence.

3. [|arXiv:1408.5911] [[|pdf], [|ps], [|other]] Effective theory of two-dimensional chiral superfluids: gauge duality and Newton-Cartan formulation [|Sergej Moroz], [|Carlos Hoyos] Comments: 14 pages Subjects: Quantum Gases (cond-mat.quant-gas) ; Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)

We present a theory of Galilean-invariant conventional and chiral p_x \pm ip_y fermionic superfluids at zero temperature in two spatial dimensions in terms of a dual gauge theory. Our formulation is general coordinate invariant. The parity-violating effects are encoded in the Wen-Zee term that gives rise to the Hall viscosity and edge current. We show that the relativistic superfluid with the Euler current reduces to the chiral superfluid in the limit c\to\infty. Using Newton-Cartan geometry we construct the covariant formulation of the effective theory and calculate the energy current.

=Aug 26= 1. [|arXiv:1408.5824] [[|pdf], [|ps], [|other]] Floquet FFLO superfluids and Majorana fermions in a shaken fermionic optical lattice [|Zhen Zheng], [|Chunlei Qu], [|Xubo Zou], [|Chuanwei Zhang] Subjects: Quantum Gases (cond-mat.quant-gas)

Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids, Cooper pairings with finite momentum, and Majorana fermions (MFs), quasiparticles with non-Abelian exchange statistics, are two topics under intensive investigation in the past several decades, but unambiguous experimental evidences for them have not been found yet in any physical system. Here we show that the recent experimentally realized cold atom shaken optical lattice provides a new pathway to realize FFLO superfluids and MFs. By tuning shaken lattice parameters (shaking frequency and amplitude), various coupling between the s- and p-orbitals of the lattice (denoted as the pseudo-spins) can be generated. We show that the combination of the inverted s- and p-band dispersions, the engineered pseudo-spin coupling, and the attractive on-site atom interaction, naturally allows the observation of FFLO superfluids as well as MFs in different parameter regions. While without interaction the system is a topological insulator (TI) with edge states, the MFs in the superfluid may be found to be in the conduction or valence band, distinguished from previous TI-based schemes that utilize edge states inside the band gap.

2. [|arXiv:1408.5653] (cross-list from quant-ph) [[|pdf], [|other]] An experimental proposal to observe non-abelian statistics of Majorana-Shockley fermions in an optical lattice [|Dong-Ling Deng], [|Sheng-Tao Wang], [|Kai Sun], [|Lu-Ming Duan] Comments: 6 pages Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con)

We propose an experimental scheme to observe non-abelian statistics with cold atoms in a two dimensional optical lattice. We show that the Majorana-Schockley modes associated with line defects obey non-abelian statistics and can be created, braided, and fused, all through adiabatic shift of the local chemical potentials. The detection of the topological qubit is transformed to local measurement of the atom number on a single lattice site. We demonstrate the robustness of the braiding operation by incorporating noise and experiential imperfections in numerical simulations, and show that the requirement fits well with the current experimental technology.

3. [|arXiv:1408.5852] [[|pdf], [|ps], [|other]] Measuring The Heat Capacity in a Bose-Einstein Condensation using Global Variables [|R.F. Shiozaki], [|G.D. Telles], [|P. Castilho], [|F.J. Poveda-Cuevas], [|S.R. Muniz], [|G. Roati], [|V. Romero-Rochin], [|V.S. Bagnato] Comments: 9 pages, 4 figures Subjects: Quantum Gases (cond-mat.quant-gas)

Phase transitions are well understood and generally followed by the behavior of the associated thermodynamic quantities, such as in the case of the λ point superfluid transition of liquid helium, which is observed in its heat capacity. In the case of a trapped Bose-Einstein condensate (BEC), the heat capacity cannot be directly measured. In this work, we present a technique able to determine the global heat capacity from the density distribution of a weakly interacting gas trapped in an inhomogeneous potential. This approach represents an alternative to models based on local density approximation. By defining a pair of global conjugate variables, we determine the total internal energy and its temperature derivative, the heat capacity. We then apply the technique to a trapped 87Rb BEC a λ-type transition dependent on the atom number is observed, and the deviations from the non-interacting, ideal gas case are discussed. Finally we discuss the chances of using this method to study the heat capacity at T→0.

=Aug 25= 1. [|arXiv:1408.5323] [[|pdf], [|other]] Topological flat bands in optical checkerboard-like lattices [|Tomi Paananen], [|Thomas Dahm] Comments: 14 pages, 6 figures Subjects: Quantum Gases (cond-mat.quant-gas)

We present comparatively simple two-dimensional and three-dimensional checkerboard-like optical lattices possessing nontrivial topological properties. By simple tuning of the parameters these lattices can have a topological insulating phase, a topological semi-metallic phase, or a trivial insulating phase. This allows study of different topological phase transitions within a single cold atom system. In the topologically nontrivial phases flat bands appear at the surfaces of the system. These surface states possess short localization lengths such that they are observable even in systems with small lattice dimensions. Our proposed lattices neither need spin-orbit coupling nor non-Abelian gauge fields to reach topologically nontrivial states.

2. [|arXiv:1408.5239] [[|pdf], [|other]] The critical velocity in the BEC-BCS crossover [|Wolf Weimer], [|Kai Morgener], [|Vijay Pal Singh], [|Jonas Siegl], [|Klaus Hueck], [|Niclas Luick], [|Ludwig Mathey], [|Henning Moritz] Comments: 5 pages, 3 figures Subjects: Quantum Gases (cond-mat.quant-gas)

We map out the critical velocity in the crossover from Bose-Einstein condensation (BEC) to Bardeen-Cooper-Schrieffer superfluidity with ultracold ^{6} Li gases. A small attractive potential is dragged along lines of constant column density. The rate of the induced heating increases steeply above a critical velocity v_c. In the same samples, we measure the speed of sound v_s by exciting density waves and compare the results to the measured values of v_c. We perform numerical simulations in the BEC regime and find very good agreement, validating the approach. In the strongly correlated regime, where theoretical predictions only exist for the speed of sound, our measurements of v_c provide a testing ground for theoretical approaches.

3. [|arXiv:1408.5209] [[|pdf], [|other]] Stroboscopic vs. Non-stroboscopic Dynamics in the Floquet Realisation of the Harper-Hofstadter Hamiltonian [|Marin Bukov], [|Anatoli Polkovnikov] Comments: 9 pages, 8 figures Subjects: Quantum Gases (cond-mat.quant-gas)

We study the stroboscopic and non-stroboscopic dynamics in the Floquet realisation of the Harper-Hofstadter Hamiltonian. We show that the former produces the evolution expected in the high-frequency limit only for observables which commute with the operator to which the driving protocol couples. On the contrary, non-stroboscopic dynamics is capable of capturing the evolution governed by the Floquet Hamiltonian of any observable associated with the effective high-frequency model. We provide exact numerical simulations for the dynamics of the density operator following a quantum cyclotron orbit on a 2\times 2 plaquette, as well as the chiral current operator flowing along the legs of a 2\times 20 ladder. The exact evolution is compared with its stroboscopic and non-stroboscopic counterparts, including finite-frequency corrections.

4.[| arXiv:1408.5148][[|pdf], [|ps],[| other]] Quantum many-body systems out of equilibrium [|J. Eisert], [|M. Friesdorf], [|C. Gogolin] Comments: 7 pages, brief review and perspectives article Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)

Closed quantum many-body systems out of equilibrium pose several long-standing problems in physics. Recent years have seen a tremendous progress in approaching these questions, not least due to experiments with cold atoms and trapped ions in instances of quantum simulations. This article provides an overview on the progress in understanding dynamical equilibration and thermalisation of closed quantum many-body systems out of equilibrium due to quenches, ramps and periodic driving. It also addresses topics such as the eigenstate thermalisation hypothesis, typicality, transport, many-body localisation, universality near phase transitions, and prospects for quantum simulation

**Aug 22**

[|arXiv:1408.4852] [ [|pdf], [|other] ] A Novel Class of $J_{eff}=1/2$ Mott Insulators [|Turan Birol], [|Kristjan Haule]   Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Materials Science (cond-mat.mtrl-sci) Discovery of new transition metal compounds with large spin orbit coupling (SOC) coexisting with strong electron-electron correlation among the $d$ electrons is essential for understanding the physics that emerges from the interplay of these two effects. In this study, we predict a novel class of $J_{eff}=1/2$ Mott insulators in a family of fluoride compounds that are previously synthesized, but not characterized extensively. First principles calculations in the level of all electron Density Functional Theory + Dynamical Mean Field Theory (DFT+DMFT) indicate that these compounds have large Mott gaps and some of them exhibit unprecedented proximity to the ideal, $SU(2)$ symmetric $J_{eff}=1/2$ limit.

[|arXiv:1408.4876] [ [|pdf], [|ps] , [|other] ] Plasmon mode as a detection of the chiral anomaly in Weyl semimetals [|Jianhui Zhou], [|Hao-Ran Chang] , [|Di Xiao]   Comments: 8 pages, 4 figures (with Supplementary material) Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall) Weyl semimetals are one kind of three dimensional gapless semimetals with nontrivial topology in the momentum space. The chiral anomaly in Weyl semimetals manifests as a charge imbalance between the Weyl nodes of opposite chiralities induced by parallel electric and magnetic fields. We investigate the chiral anomaly effect on the plasmon mode in both intrinsic and doped Weyl semimetals within the random phase approximation. We prove that the chiral anomaly gives rise to a new plasmon mode in intrinsic Weyl semimetals. We also find the chiral anomaly leads to some exotic properties in the plasmon dispersion in doped Weyl semimetals. Consequently, the unconventional plasmon mode acts as a signature of the chiral anomaly in Weyl semimetals, by which the spectrum of plasmon provides a proper way to detect the Lifshitz transition.

[|arXiv:1408.4804] [ [|pdf], [|ps] , [|other] ] Interaction-induced spontaneous symmetry breaking in bilayer graphene with an applied electric field: A renormalization group analysis of quantum multicriticality in the presence of a tunable energy gap [|Robert E. Throckmorton], [|S. Das Sarma]   Comments: 17 pages, 5 figures Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall) We develop a theory for quantum phases and quantum multicriticality in bilayer graphene in the presence of an explicit energy gap in the non-interacting spectrum by extending previous renormalization group (RG) analyses of electron-electron interactions in gapless bilayer graphene at finite temperature to include the effect of an electric field applied perpendicular to the sample. We determine the possible outcomes of the resulting RG equations, represented by "fixed rays" along which ratios of the coupling constants remain constant and map out the leading instabilities of the system for an interaction of the form of a Coulomb interaction that is screened by two parallel conducting plates placed equidistant from the electron. We find that some of the fixed rays on the "target plane" found in the zero-field case are no longer valid fixed rays, but that all four of the isolated rays are still valid. We also find five additional fixed rays that are not present in the zero-field case. We then construct maps of the leading instability (or instabilities) of the system for the screened Coulomb-like interaction as a function of the overall interaction strength and interaction range for four values of the applied electric field. We find that the pattern of leading instabilities is the same as that found in the zero-field case, namely that the system is unstable to a layer antiferromagnetic state for short-ranged interactions, to a nematic state for long-ranged interactions, and to both for intermediate-ranged interactions. However, if the interaction becomes too long-ranged or too weak, then the system will exhibit no instabilities. The ranges at which the nematic instability first appears, the antiferromagnetic instability disappears, and the nematic instability disappears all decrease with increasing applied electric field.

[|arXiv:1408.5056] [ [|pdf], [|other] ] Unifying time evolution and optimization with matrix product states [|Jutho Haegeman], [|Christian Lubich] , [|Ivan Oseledets] , [|Bart Vandereycken] , [|Frank Verstraete]   Comments: 5 pages + 5 pages supplementary material (6 figures) Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el) We show that the time-dependent variational principle provides a unifying framework for time-evolution methods and optimisation methods in the context of matrix product states. In particular, we introduce a new integration scheme for studying time-evolution, which can cope with arbitrary Hamiltonians, including those with long-range interactions. Rather than a Suzuki-Trotter splitting of the Hamiltonian, which is the idea behind the adaptive time-dependent density matrix renormalization group method or time-evolving block decimation, our method is based on splitting the projector onto the matrix product state tangent space as it appears in the Dirac-Frenkel time-dependent variational principle. We discuss how the resulting algorithm resembles the density matrix renormalization group (DMRG) algorithm for finding ground states so closely that it can be implemented by changing just a few lines of code and it inherits the same stability and efficiency. In particular, our method is compatible with any Hamiltonian for which DMRG can be implemented efficiently and DMRG is obtained as a special case of imaginary time evolution with infinite time step.

Aug 21
[|arXiv:1408.4557] [ [|pdf], [|ps] , [|other] ] Fluctuation Effects on the Transport Properties of Unitary Fermi Gases [|Boyang Liu], [|Hui Zhai] , [|Shizhong Zhang]   Comments: 8 pages and 4 figures including supplementary materials Subjects: Quantum Gases (cond-mat.quant-gas) In this letter, we investigate the fluctuation effects on the transport properties of unitary Fermi gases in the vicinity of the superfluid transition temperature $T_c$. Based on the time-dependent Ginzburg-Landau formalism of the BEC-BCS crossover, we investigate both the residual resistivity below $T_c$ induced by phase slips and the paraconductivity above $T_c$ due to pair fluctuations. These two effects have been well studied in the weak coupling BCS superconductor, and here we generalize them to the unitary regime of ultracold Fermi gases. We find that while the residual resistivity below $T_c$ increases as one approaches the unitary limit, consistent with recent experiments, the paraconductivity exhibits non-monotonic behavior. Our results can be verified with the recently developed transport apparatus using mesoscopic channels.

[|arXiv:1408.4473] [ [|pdf], [|ps] , [|other] ] Critical phenomena in one dimension from a Bethe ansatz perspective [|Xiwen Guan] Comments: a brief review, 21 pages, 15 figures Journal-ref: International Journal of Modern Physics B, 28, 1430015 (2014) Subjects: Quantum Gases (cond-mat.quant-gas) This article briefly reviews recent theoretical developments in quantum critical phenomena in one-dimensional (1D) integrable quantum gases of cold atoms. We present a discussion on quantum phase transitions, universal thermodynamics, scaling functions and correlations for a few prototypical exactly solved models, such as the Lieb-Liniger Bose gas, the spin-1 Bose gas with antiferromagnetic spin-spin interaction, the two-component interacting Fermi gas as well as spin-3/2 Fermi gases. We demonstrate that their corresponding Bethe ansatz solutions provide a precise way to understand quantum many-body physics, such as quantum criticality, Luttinger liquids, the Wilson ratio, Tan's Contact, etc. These theoretical developments give rise to a physical perspective using integrability for uncovering experimentally testable phenomena in systems of interacting bosonic and fermonic ultracold atoms confined to 1D.

[|arXiv:1408.4672] [ [|pdf], [|other] ] Detecting two-site spin-entanglement in many-body systems with local particle-number fluctuations [|Leonardo Mazza], [|Davide Rossini] , [|Rosario Fazio] , [|Manuel Endres]   Subjects: Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph) We derive experimentally measurable lower bounds for the two-site entanglement of the spin-degrees of freedom of many-body systems with local particle-number fluctuations. Our method aims at enabling the spatially resolved detection of spin-entanglement in Hubbard systems using high-resolution imaging in optical lattices. A possible application is the observation of entanglement generation and spreading during spin impurity dynamics, for which we provide numerical simulations. More generally, the scheme can simplify the entanglement detection in ion chains, Rydberg atoms, or similar atomic systems.

[|arXiv:1408.4457] [ [|pdf], [|other] ] Fractionally quantized charge pumping in a one-dimensional superlattice [|Pasquale Marra], [|Roberta Citro] , [|Carmine Ortix]   Comments: 6 pages, 4 figures, submitted to PRL Subjects: Quantum Gases (cond-mat.quant-gas) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall) A one-dimensional quantum charge pump transfers a quantized charge in each pumping cycle. This quantization is topologically robust being analogous to the quantum Hall effect. The charge transferred in a fraction of the pumping period is instead generally not quantized. We show, however, that with specific symmetries in parameter space constraining the pumping protocol, the charge transferred at well-defined fractions of the pumping period is quantized as integer fractions of the Chern number. We discuss the relevance of this fractionally quantized charge pumping for cold atomic gases in one-dimensional optical superlattices with closed as well as open geometries.

Aug 20
[|arXiv:1408.4357] (cross-list from quant-ph) [ [|pdf], [|other] ] Quantum Spin-Dimers from Chiral Dissipation in Cold Atom Chains [|Tomás Ramos], [|Hannes Pichler] , [|Andrew J. Daley] , [|Peter Zoller]   Comments: 5 pages + 7 pages supplemental material Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) We consider the non-equilibrium dynamics of a driven dissipative spin chain with chiral coupling to a 1D bosonic bath, and its atomic implementation with a two-species mixture of cold quantum gases. The reservoir is represented by a spin-orbit coupled 1D quasi-condensate of atoms in a magnetized phase, while the spins are identified with motional states of a separate species of atoms in an optical lattice. The chirality of reservoir excitations allows the spins to couple differently to left and right moving modes, which in our atomic setup can be tuned from bidirectional to purely unidirectional. Remarkably, this leads to a pure steady state in which pairs of neighboring spins form dimers that decouple from the remainder of the chain. Our results also apply to current experiments with two-level emitters coupled to photonic waveguides.

[|arXiv:1408.4441] [ [|pdf], [|other] ] The truncated Wigner approximation on discrete phase spaces [|Johannes Schachenmayer], [|Alexander Pikovski] , [|Ana Maria Rey]   Comments: 8 pages, 5 figures Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) A phase-space method, suitable to study the many-body spin dynamics in generic spin lattice models is introduced, discussed, and tested. This technique, which we refer to as the dTWA, is based on the discrete sampling of the Wigner function instead of the continuous sampling in traditional Truncated Wigner Approximation (TWA) methods. The power of the method is demonstrated by comparisons with analytical and numerically exact calculations, which show a significant improvement compared to the TWA, e.g. by capturing revivals of spin-observables. The dTWA is demonstrated to not only correctly reproduce dynamics of one-particle observables but also two-point correlations and spin squeezing, a property relying on entanglement. This method thus opens the possibility to study the quantum dynamics in long-range spin models, accessible to recent state-of-the-art experiments, in regimes where other numerical techniques are inapplicable.

Aug 19
[|arXiv:1408.3669] [ [|pdf], [|other] ] Topology and interactions in a frustrated slab: tuning from Weyl semi-metal to ${\cal C}>1$ fractional Chern insulators [|E.J. Bergholtz], [|Z. Liu] , [|M. Trescher] , [|R. Moessner] , [|M. Udagawa]   Comments: 5+5 pages Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph) We show that, quite generically, a [111] slab of spin-orbit coupled pyrochlore lattice exhibits surface states whose constant energy curves take the shape of Fermi arcs, localized to different surfaces depending on their quasi-momentum. Remarkably, these persist independently of the existence of Weyl points in the bulk. Considering interacting electrons in slabs of finite thickness, we find a plethora of known fractional Chern insulating phases, to which we add the discovery of a new higher Chern number state which is likely a generalization of the Moore-Read fermionic fractional quantum Hall state. By contrast, in the three-dimensional limit, we argue for the absence of gapped states of the flat surface band due to a topologically protected coupling of the surface to gapless states in the bulk. We comment on generalizations as well as experimental perspectives in thin slabs of pyrochlore iridates.

[|arXiv:1408.4027] [ [|pdf], [|other] ] Floquet edge states in a harmonically driven integer quantum Hall system [|Zhenyu Zhou], [|Indubala I. Satija] , [|Erhai Zhao]   Comments: 9 pages, 9 figures Subjects: Quantum Gases (cond-mat.quant-gas) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph) Recent theoretical work on time-periodically kicked Hofstadter model found robust counter-propagating edge modes. It remains unclear how ubiquitously such anomalous modes can appear, and what dictates their robustness against disorder. Here we shed further light on the nature of these modes by analyzing a simple type of periodic driving where the hopping along one spatial direction is modulated sinusoidally with time while the hopping along the other spatial direction is kept constant. We obtain the phase diagram for the quasienergy spectrum at flux 1/3 as the driving frequency $\omega$ and the hopping anisotropy are varied. A series of topologically distinct phases with counter-propagating edge modes appear due to the harmonic driving, similar to the case of a periodically kicked system studied earlier. We analyze the time dependence of the pair of Floquet edge states localized at the same edge, and compare their Fourier components in the frequency domain. In the limit of small modulation, one of the Floquet edge mode within the pair can be viewed as the edge mode originally living in the other energy gap shifted in quasienergy by $\hbar \omega$, i.e., by absorption or emission of a "photon" of frequency $\omega$. Our result suggests that counter-propagating Floquet edge modes are generic features of periodically driven integer quantum Hall systems, and not tied to any particular driving protocol. It also suggests that the Floquet edge modes would remain robust to any static perturbations that do not destroy the chiral edge modes of static quantum Hall states.

[|arXiv:1408.3787] (cross-list from quant-ph) [ [|pdf], [|other] ] Experimental implementation of adiabatic passage between different topological orders [|Xinhua Peng], [|Zhihuang Luo] , [|Supeng Kou] , [|Dieter Suter] , [|Jiangfeng Du]   Comments: 5 pages, 4 figures + Supplementary Materials; Accepted in Phys. Rev. Lett. (2014) Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el) Topological orders are exotic phases of matter existing in strongly correlated quantum systems, which are beyond the usual symmetry description and cannot be distinguished by local order parameters. Here we report an experimental quantum simulation of the Wen-plaquette spin model with different topological orders in a nuclear magnetic resonance system, and observe the adiabatic transition between two $Z_2$ topological orders through a spin-polarized phase by measuring the nonlocal closed-string (Wilson loop) operator. Moreover, we also measure the entanglement properties of the topological orders. This work confirms the adiabatic method for preparing topologically ordered states and provides an experimental tool for further studies of complex quantum systems.

Aug 18
[|arXiv:1408.3424] [ [|pdf], [|ps] , [|other] ] Fractional Quantum Hall Effect in Hofstadter Butterflies of Dirac Fermions [|Areg Ghazaryan], [|Tapash Chakraborty] , [|Pekka Pietilainen]   Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) We report on the influence of a periodic potential on the fractional quantum Hall effect (FQHE) states in monolayer graphene. We have shown that for two values of the magnetic flux per unit cell (one-half and one-third flux quantum) an increase of the periodic potential strength results in a closure of the FQHE gap and appearance of gaps due to the periodic potential. In the case of one-half flux quantum this causes a change of the ground state and consequently the change of the momentum of the system in the ground state. While there is also crossing between low-lying energy levels for one-third flux quantum the ground state does not change with the increase of the periodic potential strength and is always characterized by the same momentum. Finally, it is shown that for one-half flux quantum the emergent gaps are due entirely to the electron-electron interaction, whereas for the one-third flux quantum per unit cell these are due to both non-interacting electrons (Hofstadter butterfly pattern) and the electron-electron interaction.

[|arXiv:1408.3413] [ [|pdf], [|other] ] Anomalous diffusion and Griffiths effects near the many-body localization transition [|Kartiek Agarwal], [|Sarang Gopalakrishnan] , [|Michael Knap] , [|Markus Mueller] , [|Eugene Demler]   Comments: 6 pages, 3 figures + Supplemental Material Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn) ; Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el) We explore the high-temperature dynamics of the disordered, one-dimensional XXZ model near the many-body localization (MBL) transition, focusing on the delocalized (i.e., "metallic") phase. In the vicinity of the transition, we find that this phase has the following properties: (i) Local magnetization fluctuations relax subdiffusively; (ii) the a.c. conductivity vanishes near zero frequency as a power law; (iii) the distribution of resistances becomes increasingly broad at low frequencies, approaching a power law in the zero-frequency limit. We argue that these effects can be understood in a unified way if the metallic phase near the MBL transition is a Griffiths phase. We establish scaling relations between the associated exponents, using exact linear-response arguments as well as a phenomenological resistor-capacitor model.

[|arXiv:1408.3509] [ [|pdf], [|ps] , [|other] ] Topological tuning in three-dimensional Dirac semimetals [|Awadhesh Narayan], [|Domenico Di Sante] , [|Silvia Picozzi] , [|Stefano Sanvito]   Comments: 4 pages, 4 figures Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Materials Science (cond-mat.mtrl-sci) We study with first-principles methods the interplay between bulk and surface Dirac fermions in three dimensional Dirac semimetals. By combining density functional theory with the coherent potential approximation, we reveal a topological phase transition in alloy Na$_3$Bi$_{1-x}$Sb$_{x}$, where the material goes from a Dirac semimetal to a trivial insulator upon changing Sb concentration. Tuning the composition allows us to engineer the position of the bulk Dirac points in reciprocal space. Interestingly, the phase transition coincides with the reversal of the band ordering between the conduction and valence bands.

[|arXiv:1408.3532] [ [|pdf], [|other] ] Quantum Phases of Soft-Core Dipolar Bosons in Optical Lattices [|D. Grimmer], [|A. Safavi-Naini] , [|B. Capogrosso-Sansone] , [|Ş. G. Söyler] Comments: 5 pages, 5 figures Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Physics (quant-ph) We study the phase diagram of a system of soft-core dipolar bosons confined to a two-dimensional optical lattice layer. We assume that dipoles are aligned perpendicular to the layer such that the dipolar interactions are purely repulsive and isotropic. We consider the full dipolar interaction and perform Path Integral Quantum Monte Carlo simulations using the Worm Algorithm. Besides a superfluid phase, we find various solid and supersolid phases. We show that, unlike what was found previously for the case of nearest-neighboring interaction, supersolid phases are stabilized not only by doping the solids with particles but with holes as well. We further study the stability of these quantum phases against thermal fluctuations. Finally, we discuss pair formation and the stability of the pair checkerboard phase formed in a bilayer geometry, and suggest experimental conditions under which the pair checkerboard phase can be observed.

Aug 15
1. [|arXiv:1408.3119] [ [|pdf], [|other] ] p-wave Superfluidity by Spin-Nematic Fermi Surface Deformation [|Jan Gukelberger], [|Evgeny Kozik] , [|Lode Pollet] , [|Nikolay Prokof'ev] , [|Manfred Sigrist] , [|Boris Svistunov] , [|Matthias Troyer]   Comments: 4+1 pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas) ; Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)We study attractively interacting fermions on a square lattice with dispersion relations exhibiting strong spin-dependent anisotropy. The resulting Fermi surface mismatch suppresses the s-wave BCS-type instability, clearing the way for unconventional types of order. Unbiased sampling of the Feynman diagrammatic series using Diagrammatic Monte Carlo methods reveals a rich phase diagram in the regime of intermediate coupling strength. Instead of a proposed Cooper-pair Bose metal phase [A. E. Feiguin and M. P. A. Fisher, Phys. Rev. Lett. 103, 025303 (2009)] we find an incommensurate density wave at strong anisotropy and two different p-wave superfluid states with unconventional symmetry at intermediate anisotropy.

Aug 13
1. [|arXiv:1408.2801] [ [|pdf], [|other] ] Thermodynamics of Attractive and Repulsive Fermi Gases in Two Dimensions [|Weiran Li] Subjects: Quantum Gases (cond-mat.quant-gas) We study the attractive and repulsive two-component Fermi gas with spin imbalance in two dimensions. Using a generalized T -matrix approximation, we examine the thermodynamic properties of both attractive and repulsive contact interacting Fermi gases. The interaction strength, which is characterized by the bound state energy E b <span class="mo" style="font-family: MathJax_Main; font-size: 19px; vertical-align: 0px;">= <span class="mi" style="font-family: MathJax_Main; font-size: 19px; vertical-align: 0px;">ℏ <span class="mn" style="font-family: MathJax_Main; font-size: 13px; vertical-align: 0px;">2 <span class="mo" style="font-family: MathJax_Main; font-size: 19px; vertical-align: 0px;">/ <span class="mi" style="font-family: MathJax_Math; font-size: 19px; vertical-align: 0px;">ma <span class="mn" style="font-family: MathJax_Main; font-size: 13px; vertical-align: 0px;">22 <span class="mi" style="font-family: MathJax_Math; font-size: 13px; vertical-align: 0px;">d <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> in vacuum, can be adjusted through a Feshbach resonance. We calculate the interaction energy, compressibility and spin susceptibility of the two branches of the Fermi gas. For the repulsive branch, we also find a critical strength of interaction <span class="MathJax" style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"><span class="mi" style="font-family: MathJax_Math; font-size: 19px; vertical-align: 0px;">a <span class="mo" style="font-family: MathJax_Main; font-size: 13px; vertical-align: 0px;">( <span class="mi" style="font-family: MathJax_Math; font-size: 13px; vertical-align: 0px;">c <span class="mo" style="font-family: MathJax_Main; font-size: 13px; vertical-align: 0px;">) <span class="mn" style="font-family: MathJax_Main; font-size: 13px; vertical-align: 0px;">2 <span class="mi" style="font-family: MathJax_Math; font-size: 13px; vertical-align: 0px;">d <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> above which this metastable thermodynamic state becomes unstable. This critical value depends on the temperature and the spin imbalance (the "magnetization") of the system.

<span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">2. [|arXiv:1408.2737] [ [|pdf], [|other] ] Strongly interacting two-dimensional Fermi gases [|Jesper Levinsen], [|Meera M. Parish]   Comments: Review paper. 71 pages, 28 figures Subjects: Quantum Gases (cond-mat.quant-gas) ; Superconductivity (cond-mat.supr-con)<span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We review the current understanding of the uniform two-dimensional (2D) Fermi gas with short-range interactions. We first outline the basics of two-body scattering in 2D, including a discussion of how such a 2D system may be realized in practice using an anisotropic confining potential. We then discuss the thermodynamic and dynamical properties of 2D Fermi gases, which cold-atom experiments have only just begun to explore. Of particular interest are the different pairing regimes as the interparticle attraction is varied; the superfluid transition and associated finite-temperature phenomenology; few-body properties and their impact on the many-body system; the Fermi polaron problem; and the symmetries underlying the collective modes. Where possible, we include the contributions from 2D experiment. An underlying theme throughout is the effect of the quasi-2D geometry, which we view as an added richness to the problem rather than an unwanted complication.

<span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">3. [|arXiv:1408.2533] [ [|pdf], [|other] ] Characterization of Bose-Hubbard Models with Quantum Non-demolition Measurements [|B. Rogers], [|M. Paternostro] , [|J. F. Sherson] , [|G. De Chiara]   Comments: 8 pages, 9 figures Subjects: Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph)<span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We propose a scheme for the detection of quantum phase transitions in the 1D Bose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the non-demolition measurement technique of quantum polarization spectroscopy. We use collective measurements of the effective total angular momentum of a particular spatial mode to characterise the Mott insulator to superfluid phase transition in the BH model, and the Haldane insulator to density wave phase transition in the EBH model. We extend the application of collective measurements to the ground states at various deformations of a super-lattice potential.

Aug 12
1. [|arXiv:1408.2269] (cross-list from cond-mat.str-el) [ [|pdf], [|other] ] Solving fermion sign problem in quantum Monte Carlo by Majorana representation [|Zi-Xiang Li], [|Yi-Fan Jiang] , [|Hong Yao]   Comments: 4.5 pages, 1 figure Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Quantum Gases (cond-mat.quant-gas); High Energy Physics - Lattice (hep-lat)<span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">In this paper, we discover a new quantum Monte Carlo (QMC) method to solve the fermion sign problem in interacting fermion models by employing Majorana representation of complex fermions. We call it "Majorana QMC" (MQMC). Especially, MQMC is fermion sign free in simulating a class of spinless fermion models on bipartite lattices with arbitrary range of interactions. To the best of our knowledge, MQMC is the first auxiliary field QMC method to solve fermion sign problem in spinless (more generally, odd number of species) fermion models. MQMC simulations can be performed efficiently both at finite and zero temperatures. We believe that MQMC has potential of paving a new avenue to solve fermion sign problem in more generic fermionic models.

//**Aug 8**// 1. [|arXiv:1408.1411] [[|pdf], [|ps], [|other]] [|Ivana Vasic], [|Alexandru Petrescu], [|Karyn Le Hur], [|Walter Hofstetter] Recent experiments in ultracold atoms and photonic analogs have reported the implementation of artificial gauge fields in lattice systems, facilitating the realization of topological phases. Motivated by such advances, we investigate the Haldane honeycomb lattice tight-binding model, for bosons with local interactions at the average filling of one boson per site. We analyze the ground state phase diagram and uncover three distinct phases: a uniform superfluid (SF), a chiral superfluid (CSF) and a plaquette Mott insulator with local current loops (PMI). Nearest-neighbor and next-nearest neighbor currents distinguish CSF from SF, and the phase transition between them is first order. We apply bosonic dynamical mean field theory and exact diagonalization to obtain the phase diagram, complementing numerics with calculations of excitation spectra in strong and weak coupling perturbation theory. The characteristic density fluctuations, current correlation functions, and excitation spectra are measurable in ultracold atom experiments.
 * Chiral Bosonic Phases on the Haldane Honeycomb Lattice**

2. [|arXiv:1408.1691] [[|pdf], [|other]] [|Aron J. Beekman] Spontaneous symmetry breaking is revered by students of high-energy physics and condensed matter alike as the important mechanism for creating order out of beautifully symmetric equations of nature. Within the collection of spontaneously broken states, the Heisenberg ferromagnet has long been known to be an outlier, for instance it is an exact eigenstate of the Hamiltonian and as such has no quantum fluctuations. It also breaks time-reversal symmetry spontaneously, and has a reduced number of Nambu-Goldstone modes. The recent explanations of the counting of Nambu-Goldstone modes in non-relativistic systems lead one to wonder whether other properties of the ferromagnet carry over to such states of matter. Here I establish criteria for the absence of quantum fluctuations and the other specialties of the ferromagnet. In particular, it is not sufficient that the order parameter commute with the Hamiltonian.
 * Criteria for the absence of quantum fluctuations after spontaneous symmetry breaking**

//**Aug 7**// 1. [|arXiv:1408.1326] [[|pdf], [|ps], [|other]] [|Yvan Castin], [|Igor Ferrier-Barbut] , [|C. Salomon] We determine \'a la Landau the critical velocity vLc of a moving impurity in a Fermi superfluid, that is by restricting to the minimal excitation processes of the superfluid. vLc is then the minimal velocity at which these processes are energetically allowed. The Fermi superfluid actually exhibits two excitation branches~: one is the fermionic pair-breaking excitation, as predicted by BCS theory; the other one is bosonic and sets pairs into motion, as predicted by Anderson's RPA. vLc is the smallest of the two corresponding critical velocities vLc,f and vLc,b. In the parameter space (superfluid interaction strength, fermion-to-impurity mass ratio), we identify two transition lines, corresponding to a discontinuity of the first-order and second-order derivatives of vLc. These two lines meet in a triple point and split the plane in three domains. We briefly extend this analysis to the very recently realized case at ENS, where the moving object in the Fermi superfluid is a weakly interacting Bose superfluid of impurities, rather than a single impurity. For a Bose chemical potential much smaller than the Fermi energy, the topology of the transition lines is unaffected; a key result is that the domain vLc=c, where c is the sound velocity in the Fermi superfluid, is turned into a domain vLc=c+cB, where cB is the sound velocity in the Bose superfluid, with slightly shifted boundaries.
 * The Landau critical velocity for a particle in a Fermi superfluid**

2. [|arXiv:1408.1289] [[|pdf], [|other]] [|L. Dominici], [|D. Colas], [|S. Donati], [|J. P. Restrepo Cuartas], [|M. De Giorgi], [|D. Ballarini], [|G. Guirales], [|J. C. López Carreño], [|A. Bramati], [|G. Gigli], [|E. del Valle], [|F. P. Laussy], [|D. Sanvitto] We report the experimental observation and control of space and time-resolved light-matter Rabi oscillations in a microcavity. Our setup precision and the system coherence are so high that coherent control can be implemented with amplification or switching off of the oscillations and even erasing of the polariton density by optical pulses. The data is reproduced by a fundamental quantum optical model with excellent accuracy, providing new insights on the key components that rule the polariton dynamics.
 * Ultrafast control of Rabi oscillations in a polariton condensate**

//**Aug 6**// 1. [|arXiv:1408.0944] [[|pdf], [|other]] [|A. A. Wood], [|L. M. Bennie], [|A. Duong], [|M. Jasperse], [|L. D. Turner], [|R. P. Anderson] We have realized a magnetic tensor gradiometer by interferometrically measuring the relative phase between two spatially separated Bose-Einstein condensates (BECs). We perform simultaneous Ramsey interferometry of the proximate 87Rb spin-1 condensates in freefall and infer their relative Larmor phase -- and thus the differential magnetic field strength -- with a common-mode phase noise suppression exceeding 50dB. By appropriately biasing the magnetic field and separating the BECs along orthogonal directions, we measure the magnetic field gradient tensor of ambient and applied magnetic fields with a nominal precision of 30μGcm−1 and a sensor volume of 2×10−5mm3. We predict a spin-projection noise limited magnetic energy resolution of order ℏ for typical Zeeman coherence times of trapped condensates with this scheme, even with the low measurement duty cycle inherent to BEC experiments.
 * Magnetic tensor gradiometry using Ramsey interferometry of spinor condensates**

2. [|arXiv:1408.1041] [[|pdf], [|other]] [|Johannes Schachenmayer], [|Lode Pollet], [|Matthias Troyer], [|Andrew J. Daley] We study the out-of-equilibrium dynamics of bosonic atoms in a 1D optical lattice, after the ground-state is excited by a single spontaneous emission event, i.e. after an absorption and re-emission of a lattice photon. This is an important fundamental source of decoherence for current experiments, and understanding the resulting dynamics and changes in the many-body state is important for controlling heating in quantum simulators. Previously it was found that in the superfluid regime, simple observables relax to values that can be described by a thermal distribution on experimental time-scales, and that this breaks down for strong interactions (in the Mott insulator regime). Here we expand on this result, investigating the relaxation of the momentum distribution as a function of time, and discussing the relationship to eigenstate thermalization. For the strongly interacting limit, we provide an analytical analysis for the behavior of the system, based on an effective low-energy Hamiltonian in which the dynamics can be understood based on correlated doublon-holon pairs.
 * Thermalization of strongly interacting bosons after spontaneous emissions in optical lattices**

3. [|arXiv:1408.0928] [[|pdf], [|other]] [|Guido Pagano], [|Marco Mancini], [|Giacomo Cappellini], [|Pietro Lombardi], [|Florian Schäfer], [|Hui Hu], [|Xia-Ji Liu], [|Jacopo Catani], [|Carlo Sias], [|Massimo Inguscio], [|Leonardo Fallani]
 * A one-dimensional liquid of fermions with tunable spin**

Correlations in systems with spin degree of freedom are at the heart of fundamental phenomena, ranging from magnetism to superconductivity. The effects of correlations depend strongly on dimensionality, a striking example being one-dimensional (1D) electronic systems, extensively studied theoretically over the past fifty years. However, the experimental investigation of the role of spin multiplicity in 1D fermions - and especially for more than two spin components - is still lacking. Here we report on the realization of 1D, strongly-correlated liquids of ultracold fermions interacting repulsively within SU(N) symmetry, with a tunable number N of spin components. We observe that static and dynamic properties of the system deviate from those of ideal fermions and, for N>2, from those of a spin-1/2 Luttinger liquid. In the large-N limit, the system exhibits properties of a bosonic spinless liquid. Our results provide a testing ground for many-body theories and may lead to the observation of fundamental 1D effects.

4. [|arXiv:1408.1055] [[|pdf], [|other]] [|Daniel Barredo], [|Henning Labuhn], [|Sylvain Ravets], [|Thierry Lahaye], [|Antoine Browaeys], [|Charles S. Adams] We study coherent excitation "hopping" in a spin chain realized using highly-excited individually addressable Rydberg atoms. The dynamics are fully described in terms of an XY spin Hamiltonanian with a long range resonant dipole-dipole coupling that scales as the inverse third power of the lattice spacing, C3/R3. The experimental data demonstrate the importance of next neighbor interactions which are manifest as revivals in the excitation dynamics. The results suggest that arrays of Rydberg atoms are ideally suited to large scale, high-fidelity quantum simulation of spin dynamics.
 * Coherent Excitation Transfer in a "Spin Chain" of Three Rydberg Atoms**

5. [|arXiv:1408.0843] [[|pdf], [|other]] [|T. S. Jackson], [|G. Möller], [|R. Roy] The fractional quantum Hall effect (FQHE) provides some indication of the vast range of novel phenomena which can arise in a topologically ordered state in the presence of strong interactions. The possibility of realizing FQH-like phases in lattice models has attracted intense interest recently, both as a more experimentally accessible venue for FQH phenomena as well as a generalization of FQH physics which has been largely unexplored theoretically. For both of these purposes, we investigate the physical relevance of geometric conditions previously derived by one of us as quantifying deviations from the Landau level physics of the FQHE. We conduct extensive numerical many-body simulations on a variety of lattice models and find remarkable correlation between these criteria and the many-body gap. This leads us to propose a "geometric stability hypothesis," namely that these single-particle criteria usefully quantify destabilizing effects on many-body FQH-like phases.
 * Geometric stability of topological lattice phases**

1. [|arXiv:1408.0769] [[|pdf], [|ps], [|other]] [|Tobias Graß], [|Ravindra W. Chhajlany], [|Christine A. Muschik], [|Maciej Lewenstein] We study the Mott phase of three-component bosons, with one particle per site, in an optical lattice by mapping it onto an SU(3) spin model. In the simplest case of full SU(3) symmetry, one obtains a ferromagnetic Heisenberg model. Introducing an SU(3) analog of spin-orbit coupling, additional spin-spin interactions are generated. We first consider the scenario of spin-dependent hopping phases, leading to Dzyaloshinskii-Moriya-type interactions. They result in the formation of spiral spin textures, which in one dimension can be understood by a local unitary transformation. Applying classical Monte Carlo simulations, we extend our study to two-dimensional systems, and systems with "true" spin-orbit coupling, involving spin-changing hoppings.
 * //Aug 5//**
 * Spiral spin textures of bosonic Mott insulator with SU(3) spin-orbit coupling**

2. [|arXiv:1408.0662] [[|pdf], [|other]] [|Benoît Vermersch], [|Matthias Punk], [|Alexander W. Glaetzle], [|Christian Gross], [|Peter Zoller] We describe the dynamical preparation of anisotropic crystalline phases obtained by laser-exciting ultracold Alkali atoms to Rydberg p-states where they interact via anisotropic van der Waals interactions. We develop a time- dependent variational mean field ansatz to model large, but finite two-dimensional systems in experimentally accessible parameter regimes, and we present numerical simulations to illustrate the dynamical formation of anisotropic Rydberg crystals.
 * Dynamical preparation of laser-excited anisotropic Rydberg crystals in 2D optical lattices**

//**Aug 4**// 1. [|arXiv:1408.0206] [[|pdf], [|other]] [|A. Dirks], [|K. Mikelsons], [|H.R. Krishnamurthy], [|J.K. Freericks] In the vicinity of a Feshbach resonance, a system of ultracold atoms on an optical lattice undergoes rich physical transformations which involve molecule formation and hopping of molecules on the lattice and thus goes beyond a single-band Hubbard model description. We propose to probe the behavior of this system with a harmonic modulation of the magnetic field, and thus of the scattering length, across the Feshbach resonance, as an alternative to lattice-depth modulation spectroscopy. In the regime in which the single-band Hubbard model is still valid, we provide simulation data for this type of spectroscopy. The method may uncover a route towards the efficient creation of ultracold molecules and provides an alternate means for lattice modulation spectroscopy.
 * Feshbach modulation spectroscopy**