Mar 2014

| Mar 24-Mar 28, Bo Liu | Mar 28 | Mar 27 | | Mar 26 | | | Mar 25 | | | Mar 24 | Mar 17 - Mar 21, Zhenyu Zhou | Mar 10-Mar 14, Zhifang Xu | | Mar 14 | Mar 13 | Mar 12 | Mar 10 | Mar 3-Mar 7, Jinlong Yu

Mar 24-Mar 28, Bo Liu


Mar 28

1. arXiv:1403.6876 [pdf, other]
A long-lived Higgs mode in a two-dimensional confined Fermi gas
Georg M. Bruun
The Higgs mode corresponds to the collective motion of particles due to the vibrations of an invisible field. It plays a fundamental role for our understanding of both low and high energy physics, giving elementary particles their mass and leading to collective modes in condensed matter and nuclear systems. The Higgs mode has been observed in a limited number of table-top systems, where it however is characterised by a short lifetime due to decay into a continuum of modes. A major goal which has remained elusive so far, is therefore to realise a long-lived Higgs mode in a controllable system. Here, we show how an undamped Higgs mode can be observed unambiguously in a Fermi gas in a two-dimensional trap, close to a quantum phase transition between a normal and a superfluid phase. We develop a first-principles theory of the pairing and the associated collective modes, which is quantitatively reliable when the pairing energy is much smaller than the trap level spacing, yet simple enough to allow the derivation of analytical results. The theory includes the trapping potential exactly, which is demonstrated to stabilize the Higgs mode by making its decay channels discrete. Our results show how atoms in micro-traps can unravel properties of a long-lived Higgs mode, including the role of confinement and finite size effects.



Mar 27

1. arXiv:1403.6653 (cross-list from nlin.PS) [pdf, ps, other]
Localized modes in two-dimensional Schroedinger lattices with a pair of nonlinear sites
Valeriy A. Brazhnyi, Boris A. Malomed
We address the existence and stability of localized modes in the two-dimensional (2D) linear Schroedinger lattice with two symmetric nonlinear sites embedded into it, and a generalization for moderately localized nonlinearity featuring two distinct symmetric maxima. The latter setting admits a much greater variety of localized modes. Symmetric, antisymmetric, and asymmetric discrete solitons are found, and a subcritical bifurcation, accounting for the spontaneous symmetry breaking (SSB) of the symmetric modes and transition to asymmetric ones, is identified. Existence and stability of more complex 2D solutions in the form of discrete symmetric and asymmetric vortices are also discussed.

Mar 26

1.arXiv:1403.6162 (cross-list from cond-mat.stat-mech) [pdf, other]
Entropy is in Flux
Leo P. Kadanoff
The science of thermodynamics was put together in the Nineteenth Century to describe large systems in equilibrium. One part of thermodynamics defines entropy for equilibrium systems and demands an ever-increasing entropy for non-equilibrium ones. However, starting with the work of Ludwig Boltzmann in 1872, and continuing to the present day, various models of non-equilibrium behavior have been put together with the specific aim of generalizing the concept of entropy to non-equilibrium situations. This kind of entropy has been termed {\em kinetic entropy} to distinguish it from the thermodynamic variety. Knowledge of kinetic entropy started from Boltzmann's insight about his equation for the time dependence of gaseous systems. In this paper, his result is stated as a definition of kinetic entropy in terms of a local equation for the entropy density. This definition is then applied to Landau's theory of the Fermi liquid thereby giving the kinetic entropy within that theory. 
Entropy has been defined and used for a wide variety of situations in which a condensed matter system has been allowed to relax for a sufficient period so that the very most rapid fluctuations have been ironed out. One of the broadest applications of non-equilibrium analysis considers quantum degenerate systems using Martin-Schwinger Green's functions\cite{MS} as generalized of Wigner functions, g< and g>. This paper describes once again these how the quantum kinetic equations for these functions give locally defined conservation laws for mass momentum and energy. In local thermodynamic equilibrium, this kinetic theory enables a reasonable local definition of entropy density. However, when the system is outside of local equilibrium, this definition fails. It is speculated that quantum entanglement is the source of this failure.
Mar 25

1.arXiv:1403.6041 [pdf, ps, other]
The Berry Curvature as a Magnetic Field in Momentum Space
Hannah M. Price, Tomoki Ozawa, Iacopo Carusotto
Artificial magnetism in momentum space can be engineered from the geometrical properties of energy bands. We show that the Berry curvature acts as a magnetic field in momentum space in the effective quantum Hamiltonian of a wide-range of systems. The effective Hamiltonian is equivalent to the textbook magnetic Hamiltonian, with the roles of momentum and position reversed. This duality has important implications for research into solid-state materials, spin-orbit coupling, ultracold gases and photonic systems. We propose a simple experiment that will demonstrate the advantages of this approach and that will also constitute the first realisation of magnetism on a torus.
Mar 24

1. arXiv:1403.5530 (cross-list from cond-mat.other) [pdf, other]
Universality of spin-relaxation for spin 1/2 particles diffusing over magnetic field inhomogeneities in the adiabatic regime
M. Guigue, G. Pignol, R. Golub, A. K. Petukhov
We present a theoretical analysis of spin relaxation, for a polarized gas of spin 1/2 particles undergoing restricted adiabatic diffusive motion within a container of arbitrary shape, due to magnetic field inhomogeneities of arbitrary shape.

Mar 17 - Mar 21, Zhenyu Zhou
Wed, 19 Mar 2014

1. **arXiv:1403.4242** [**pdf**, **ps**, **other**]
Stabilizing the false vacuum: Mott skyrmions
Márton Kanász-Nagy, Balázs Dóra, Eugene A. Demler, Gergely Zaránd
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles -- emerging almost necessarily in any grand unified theory and responsible for charge quantization -- remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures and investigate their properties in detail. We show furthermore that the spectrum of the excitations of the superfluid and their quantum numbers change dramatically in the presence of the skyrmion, and they reflect the presence of a trapped monopole, as imposed by the skyrmion's topology.

2.**arXiv:1403.4568** (cross-list from cond-mat.stat-mech) [**pdf**, **other**]
The XYZ chain with Dzyaloshinsky-Moriya interactions: from spin-orbit-coupled lattice bosons to interacting Kitaev chains
Sebastiano Peotta, Leonardo Mazza, Ettore Vicari, Marco Polini, Rosario Fazio, Davide Rossini
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas)
Using the density-matrix renormalization-group algorithm (DMRG) and a finite-size scaling analysis, we study the properties of the one-dimensional completely-anisotropic spin-1/2 XYZ model with Dzyaloshinsky-Moriya (DM) interactions. The model shows a rich phase diagram: depending on the value of the coupling constants, the system can display different kinds of ferromagnetic order and Luttinger-liquid behavior. Transitions from ferromagnetic to Luttinger-liquid phases are first order. We thoroughly discuss the transition between different ferromagnetic phases, which, in the absence of DM interactions, belongs to the XX universality class. We provide evidence that the DM exchange term leads to a splitting of this critical line into two Ising-like transitions. In between, an interesting disordered phase appears. Our study sheds light on the general problem of strongly-interacting spin-orbit-coupled bosonic gases trapped in an optical lattice and can be used to characterize the topological properties of superconducting nanowires in the presence of an external magnetic field.

Thu, 20 Mar 2014

1. **arXiv:1403.4761** [**pdf**, **other**]
Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions
F. Scazza, C. Hofrichter, M. Höfer, P. C. De Groot, I. Bloch, S. Fölling
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
We report on the direct observation of spin-exchanging interactions in a two-orbital SU(N)-symmetric quantum gas of ytterbium in an optical lattice. The two orbital states are represented by two different (meta-)stable electronic configurations of fermionic 173Yb. A strong spin-exchange between particles in the two separate orbitals is mediated by the contact interaction between atoms, which we characterize by clock shift spectroscopy in a 3D optical lattice. We find the system to be SU(N)-symmetric within our measurement precision and characterize all relevant scattering channels for atom pairs in combinations of the ground and the excited state. Elastic scattering between the orbitals is dominated by the antisymmetric channel, which leads to the strong spin-exchange coupling. The exchange process is directly observed, by characterizing the dynamic equilibration of spin imbalances between two large ensembles in the two orbital states, as well as indirectly in atom pairs via interaction shift spectroscopy in a 3D lattice. The realization of a stable SU(N)-symmetric two-orbital Hubbard Hamiltonian opens the route towards experimental quantum simulation of condensed-matter models based on orbital interactions, such as the Kondo lattice model.

2. **arXiv:1403.4800** (cross-list from quant-ph) [**pdf**, **ps**, **other**]
Dicke super-radiance as non-destructive probe for super-fluidity in optical lattices
Nicolai ten Brinke, Ralf Schützhold
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
We study Dicke super-radiance as collective and coherent absorption and emission of photons from an ensemble of ultra-cold atoms in an optical lattice. Since this process depends on the coherence properties of the atoms (e.g., super-fluidity), it can be used as a probe for their quantum state. This detection method is less invasive than time-of-flight experiments or direct (projective) measurements of the atom number (or parity) per lattice site, which both destroy properties of the quantum state such as phase coherence.

Fri, 21 Mar 2014

**arXiv:1403.5047** [**pdf**, **other**]
Information processing with topologically protected vortex memories in exciton-polariton condensates
H. Sigurdsson, O. A. Egorov, X. Ma, I. A. Shelykh, T. C. H. Liew
Subjects: Quantum Gases (cond-mat.quant-gas)
We show that in a non-equilibrium system of an exciton-polariton condensate, where polaritons are generated from incoherent pumping, a ring-shaped pump allows for stationary vortex memory elements of topological charge m=1or m=−1. Using simple potential guides we can choose whether to copy the same charge or invert it onto another spatially separate ring pump. Such manipulation of binary information opens the possibility of a new type processing using vortices as topologically protected memory components.


Mar 10-Mar 14, Zhifang Xu
Mar 14
1.arXiv:1403.3234 [pdf, other]
Spontaneous vortex arrays in a parametrically driven polariton condensate
J. O. Hamp, A. K. Balin, F. M. Marchetti, D. Sanvitto, M. H. Szymanska
Comments: 5 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Other Condensed Matter (cond-mat.other)

We study theoretically a condensate of microcavity polaritons, driven resonantly in the optical parametric oscillator regime. Using a driven-dissipative generalized Gross-Pitaevskii equation, we model a finite system populated by a novel and experimentally viable pump with circular symmetry and radial currents. The resulting nonequilibrium superfluid is unstable to spontaneous symmetry-breaking and undergoes the formation of vortex arrays, which arise in the absence of any external field, potential, or rotation. The vortex arrays have nonzero net angular momentum and can rotate in one of two degenerate but chirally distinct states. This new phenomenon exists in a regime readily accessible to experiments, and we discuss possible experimental signatures of such an array.

Mar 13
1.arXiv:1403.2964 [pdf]
Direct observation of SU(N) orbital magnetism
X. Zhang, M. Bishof, S. L. Bromley, C. V. Kraus, M. S. Safronova, P. Zoller, A. M. Rey, J. Ye
Comments: 4 figures, 2 tables
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)

Symmetries play a fundamental role in the laws of nature. SU(N) symmetry can emerge in a quantum system with N single-particle spin states when the spin degree of freedom is decoupled from interactions. Such a system is anticipated to exhibit large degeneracy and exotic many-body behaviors. Owing to the strong decoupling between electronic-orbital and nuclear-spin degrees of freedom, alkaline-earth atoms (AEAs), prepared in the two lowest electronic states (clock states), are predicted to obey an accurate SU(N=2I+1) symmetry arising from the nuclear spin (I). So far, only indirect evidence for this symmetry exists, and the scattering parameters remain largely unknown. Here we report the first direct observation of SU(N=10) symmetry in 87Sr (I=9/2) using the state-of-the-art measurement precision offered by an ultra-stable laser. By encoding the electronic orbital degree of freedom in the two clock states, while keeping the system open to all 10 nuclear spin sublevels, we probe the non-equilibrium two-orbital SU(N) magnetism via Ramsey spectroscopy of atoms confined in an array of 2D optical traps. The motional degrees of freedom are frozen during the spin dynamics, which allows probing generic models of quantum magnetism at high temperatures. Compared with lattice models of spatially localized atoms coupled with short-range interactions, our system shows two key differences: the lattice is spanned by energy eigenvalues and the underlying interactions are long-range and nuclear spin independent. To elucidate the microscopic mechanism for SU(N) orbital physics, we model the spin-orbital dynamics and determine all relevant interaction parameters with an analytic relation between s- and p-wave scattering lengths. This work prepares for using AEAs as test-beds for iconic orbital models expected to describe transition metal oxides, heavy fermion materials, and spin liquid phases.

2. arXiv:1403.2952 [pdf, other]
Anderson tower of states and nematic order of spin-1 bosonic atoms on a 2D lattice
L. de Forges de Parny, H-Y. Yang, F. Mila
Comments: 5 pages, 4 figures + 5 pages of supplemental material
Subjects: Quantum Gases (cond-mat.quant-gas)

We investigate the structure of the spectrum of antiferromagnetically coupled spin-1 bosons on a square lattice using degenerate perturbation theory and exact diagonalizations of finite clusters. We show that the superfluid phase develops an Anderson tower of states typical of nematic long-range order with broken SU(2) symmetry, by contrast to the case of spin-1 bosons in a trap where a genuine polar superfluid ground state only appears in the presence of an external perturbation that breaks the SU(2) symmetry. We further show that this order persists into the Mott insulating phase down to zero hopping for one boson per site, and down to a critical hopping for two bosons per site, in agreement with mean-field and Quantum Monte Carlo results.

3.arXiv:1403.2792 [pdf, other]
Ultracold Fermi Gases with Emergent SU(N) Symmetry
M. A. Cazalilla, A. M. Rey
Comments: Review article (43 pages, 7 figures); comments are welcome
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

We review recent experimental and theoretical progress on ultracold alkaline-earth Fermi gases with emergent SU
external image 0028.pngexternal image 004E.pngexternal image 0029.png
symmetry. Emphasis is placed on describing the ground-breaking experimental achievements of recent years. The latter include the cooling to below quantum degeneracy of various isotopes of ytterbium and strontium, the demonstration of optical Feshbach resonances and the optical Stern-Gerlach effect, the realization of a Mott insulator of
external image 0031.pngexternal image 0037.pngexternal image 0033.png
Yb atoms, the creation of various kinds of Fermi-Bose mixtures and the observation of many-body physics in optical lattice clocks. On the theory side, we survey the zoo of phases that have been predicted for both gases in a trap and loaded into an optical lattice, focusing on two and three-dimensional systems. We also discuss some of the challenges that lie ahead for the realization of such phases, such as reaching the temperature scale required to observe magnetic and more exotic quantum orders, and dealing with collisional relaxation of excited electronic levels.

4.arXiv:1403.2836 [pdf, other]
Parallel Transport and Band Theory in Crystals
Michel Fruchart (Phys-ENS), David Carpentier (Phys-ENS), Krzysztof Gawedzki (Phys-ENS)
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Mathematical Physics (math-ph)

We show that different conventions for Bloch Hamiltonians on non-Bravais lattices correspond to different natural definitions of parallel transport of Bloch eigenstates. Generically the Berry curvatures associated with these parallel transports differ, while physical quantities are naturally related to a canonical choice of the parallel transport.

Mar 12
1. arXiv:1403.2492 [pdf]
Real-Time Detection of Transient Charge Current in Floquet-Bloch State of Topological Insulators
Yoshito Onishi, Zhi Ren, Mario Novak, Kouji Segawa, Yoichi Ando, Koichiro Tanaka
Comments: 15 pages, 5 figures
Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)

In three-dimensional topological insulators (TIs), nontrivial topology in the bulk insulating state results in the surface electronic state that follows the massless Dirac equation with the spin state locked by the momentum direction. Properties in the ground state have been investigated with angular-resolved photoemission spectroscopy (ARPES), tunneling spectroscopy and conductivity measurements. Optically excited Dirac fermions provide a useful platform for studying the non-equilibrium dynamics of relativistic particles interacting with electromagnetic field. Recently, their electric-field response such as the magneto-optical effect in the terahertz (THz) range has been studied with optical pump-probe measurements and time-resolved ARPES. Theoretically, spin-selective excitations by circularly polarized light are expected to induce an asymmetric distribution in the k-space and drive a macroscopic charge current, which has actually been observed by two-terminal sensing. However, the breaking of the symmetry due to the attachment of electrodes hinders clear understanding of the driving mechanism. Also, time-resolved techniques that are necessary for understanding the transient dynamics of the induced surface charge current have not been applied to these intriguing phenomena. Here we report our observation of THz emissions from an intrinsic TI material, Bi${}_{2-x}$Sb${}_x$Te${}_{3-y}$Se${}_y$ $[(x,y) = (0.5,1.3)$ and $(1,2)]$, under the illumination of circularly polarized femtosecond pulses. The THz emission strongly depends on the helicity of the excitation pulses, indicating that its origin is the surface charge current. Nevertheless, we observed three-fold symmetry in the azimuthal-angle dependence, which cannot stem from the simple photogalvanic effect. A plausible origin of this charge current with unusual symmetry is the formation of Floquet-Bloch states on the surface.

Mar 11
1.arXiv:1403.2018 (cross-list from cond-mat.str-el) [pdf, ps, other]
Conflicting Symmetries in Topologically Ordered Surface States of Three-dimensional Bosonic Symmetry Protected Topological Phases
Gil Young Cho, Jeffrey C. Teo, Shinsei Ryu
Comments: 9 pages plus epsilon
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas)

We study the Z2 topologically ordered surface state of three-dimensional bosonic SPT phases with the discrete symmetries G1 x G2. It has been argued that the topologically ordered surface state cannot be realized on a purely two-dimensional lattice model. We carefully examine the statement and show that the surface state should break G2 if the symmetry G1 is gauged. This manifests the conflict of the symmetry G1 and G2 on the surface of the three-dimensional SPT phase. Given that there is no such phenomena in the purely two-dimensional model, it signals that the symmetries are encoded anomalously on the surface of the three-dimensional SPT phases and that the surface state can never be realized on the purely two-dimensional models.

Mar 10
1.arXiv:1403.1739 [pdf, ps, other]
Destruction of Long-range Order by Quenching the Hopping Range in One dimension
Masaki Tezuka, Antonio M. García-García, Miguel A. Cazalilla
Comments: 6 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)

We study the dynamics in a one dimensional hard-core Bose gas with power-law hopping after an abrupt reduction of the hopping range the time-dependent density-matrix renormalization group (t-DMRG) and bosonization techniques. In particular, we focus on the destruction of the Bose-Einstein condensate (BEC), which is present in the initial state. We argue that this type of quench is akin to a sudden reduction in the effective dimensionality of the system (from d > 1 to d = 1). We identify two regimes in the evolution of the BEC fraction. For short times the decay of the BEC fraction is Gaussian while for intermediate to long times, it is well described by a stretched exponential with an exponent that depends on the initial effective dimensionality of the system. These results are potentially relevant for cold trapped-ion experiments which can simulate hard-core bosons (i.e. spins) with tunable long-range interactions.



Mar 3-Mar 7, Jinlong Yu

Mar 7
1. arXiv:1403.1474 [pdf, ps, other]
Bose-Einstein condensates in multiple well potentials from a variational path integral
Wattana Ratismith, Holger Hauptmann, Walter T. Strunz

We apply a path integral variational approach to obtain analytical expressions for condensate wave functions of an ultracold, interacting trapped Bose gases. As in many recent experiments, the particles are confined in a 1D or 3D harmonic oscillator trap which is superimposed by a periodic potential in one direction. Based on the first order cumulant expansion with respect to a harmonic trial action, and emplyoing a mean-field approximation, optimal variational parameters are obtained by minimizing an analytical expression for the ground state energy. Our largely analytical results for energy and condensate wave function are in good agreement with fully numerical calculations based on the Gross-Pitaevskii equation.

2. arXiv:1403.1284 [pdf, other]
Coarsening dynamics of binary Bose condensates
Johannes Hofmann, Stefan S. Natu, S. Das Sarma


We study the dynamics of domain formation and coarsening in a binary Bose-Einstein condensate that is quenched across a miscible-immiscible phase transition. The late-time evolution of the system is universal and governed by scaling laws for the correlation functions. We numerically determine the scaling forms and extract the critical exponents that describe the growth rate of domain size and autocorrelations. Our data is consistent with inviscid hydrodynamic domain growth, which is governed by a universal dynamical critical exponent of 1/z=0.68(2). In addition, we analyze the effect of domain wall configurations which introduce a nonanalytic term in the short-distance structure of the pair correlation function, leading to a high-momentum "Porod"-tail in the static structure factor, which can be measured experimentally.


Mar 6
1.arXiv:1403.1205 [pdf, ps, other]
Statistical properties of spectra in harmonically trapped spin-orbit coupled systems
O. V. Marchukov, A. G. Volosniev, D. V. Fedorov, A. S. Jensen, N. T. Zinner
We compute single-particle energy spectra for a one-body Hamiltonian consisting of a two-dimensional deformed harmonic oscillator potential, the Rashba spin-orbit coupling and the Zeeman term. To investigate the statistical properties of the obtained spectra as functions of deformation, spin-orbit and Zeeman strengths we examine the distributions of the nearest neighbor spacings. We find that the shapes of these distributions depend strongly on the three potential parameters. We show that the obtained shapes in some cases can be well approximated with the standard Poisson, Brody and Wigner distributions. The Brody and Wigner distributions characterize irregular motion and help identify quantum chaotic systems. We present a special choices of deformation and spin-orbit strengths without the Zeeman term which provide a fair reproduction of the fourth-power repelling Wigner distribution. By adding the Zeeman field we can reproduce a Brody distribution, which is known to describe a transition between the Poisson and linear Wigner distributions.


2. arXiv:1403.1038 [pdf, ps, other]
Beating dark-dark solitons and Zitterbewengung in spin-orbit coupled Bose-Einstein condensates
V. Achilleos, D. J. Frantzeskakis, P. G. KevrekidisWe present families of beating dark-dark solitons in spin-orbit (SO) coupled Bose-Einstein condensates. These families consist of solitons residing simultaneously in the two bands of the energy spectrum. The soliton components are characterized by two different spatial and temporal scales, which are identified by a multiscale expansion method. The solitons are "beating" ones, as they perform density oscillations with a characteristic frequency, relevant to Zitterbewengung (ZB). We find that spin oscillations may occur, depending on the parity of each soliton branch, which consequently lead to ZB oscillations of the beating dark solitons. Analytical results are corroborated by numerical simulations, illustrating the robustness of the solitons

Mar 5
1. arXiv:1403.0767 [pdf, ps, other]
Generating an effective magnetic lattice for cold atoms
Xinyu Luo, Lingna Wu, Jiyao Chen, Rong Lu, Ruquan Wang, L. You
We present a general scheme for synthesizing a spatially periodic magnetic field, or a magnetic lattice (ML), for ultracold atoms using pulsed gradient magnetic fields. Both the period and the depth of the artificial ML can be tuned, immune to atomic spontaneous emission often encountered in optical lattices. The effective Hamiltonian for our 2-dimensional ML has not been discussed previously in condensed matter physics. Its band structures show interesting features which can support topologically nontrivial phases. The technical requirements for implementing our protocol are readily available in today's cold atom experiments. Realization of our proposal will significantly expand the repertoire for quantum simulation with ultracold atoms.

2. arXiv:1403.0693 [pdf, other]
Interferometric probes of many-body localization
M. Serbyn, M. Knap, S. Gopalakrishnan, Z. Papić, N. Y. Yao, C. R. Laumann, D. A. Abanin, M. D. Lukin, E. A. Demler
We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed, coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a non-interacting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold atom systems.

3. arXiv:1403.0593 [pdf, other]
Majorana modes and $p$-wave superfluids for fermionic atoms in optical lattices
Adam Bühler, Nicolai Lang, Christina V. Kraus, Gunnar Möller, Sebastian D. Huber, Hans Peter Büchler
We present a simple approach to create a strong p-wave interaction for fermions in an optical lattice. The crucial step is that the combination of a lattice setup with different orbital states and p-wave interactions can give rise to a strong induced p-wave pairing. We identify different topological phases and demonstrate that the setup offers a natural way to explore the transition from Kitaev's Majorana wires to two-dimensional p-wave superfluids. We demonstrate how this design can induce Majorana modes at edge dislocations in the optical lattice, and we provide an experimentally feasible protocol for the observation of the non-Abelian statistics.


Mar 4
1. arXiv:1403.0294 [pdf, other]
Microscopic Origin and Universality Classes of the Efimov Three-Body Parameter
Pascal Naidon, Shimpei Endo, Masahito Ueda

The low-energy spectrum of three particles interacting via nearly resonant two-body interactions in the Efimov regime is set by the so-called three-body parameter. We show that the three-body parameter is essentially determined by the zero-energy two-body correlation. As a result, we identify two classes of two-body interactions for which the three-body parameter has a universal value in units of their effective range. One class involves the universality of the three-body parameter recently found in ultracold atom systems. The other is relevant to short-range interactions that can be found in nuclear physics and solid-state physics.