May 2015
May 4-May 7, Haiyuan Zou & Ahmet Keles, May 11-May 15 Zhifang Xu & Xuguang Yue, May 18-May 22 Bo Liu & Max, May 25-May 29, Zhenyu Zhou & Jinlong Yu
Fri, 22
1. arXiv:1505.05640 [pdf, ps, other]
Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with broken spin rotation symmetry
Yuki Endo, Daisuke Inotani, Ryo Hanai, Yoji Ohashi
We investigate the possibility that the broken spatial inversion symmetry by a trap potential induces a spin-triplet Cooper-pair amplitude in an s-wave superfluid Fermi gas. Being based on symmetry considerations, we clarify that this phenomenon may occur, when a spin rotation symmetry of the system is also broken. We also numerically confirm that a triplet pair amplitude is really induced under this condition, using a simple model. Our results imply that this phenomenon is already present in a trapped s-wave superfluid Fermi gas with spin imbalance. As an interesting application of this phenomenon, we point out that one may produce a p-wave superfluid Fermi gas, by suddenly changing the s-wave pairing interaction to a p-wave one by using the Feshbach resonance technique. Since a Cooper pair is usually classified into the spin-singlet (and even-parity) state and the spin-triplet (and odd-parity) state, our results would be useful in considering how to mix them with each other in a superfluid Fermi gas. Such admixture has recently attracted much attention in the field of non-centrosymmetric superconductivity, so that our results would also contribute to the further development of this research field, on the viewpoint of cold Fermi gas physics.
2. arXiv:1505.05791 (cross-list from cond-mat.dis-nn) [pdf, ps, other]
Superfluidity and Bose-Einstein condensation in a dipolar Bose gas with weak disorder
Boudjemaa Abdelaali
We investigate the properties of a three-dimensional homogeneous dipolar Bose gas in a weak random potential with a Gaussian correlation function at finite temperature. By using the Bogoliubov theory (beyond the mean field), we calculate the superfluid and the condensate fractions in terms of the interaction strength on the one hand and in terms of the width and the strength of the disorder on the other. The influence of the disordered potential on the second order correlation function, the ground state energy and the chemical potential is also analyzed. We find that for fixed strength and correlation length of the disorder potential, the dipole-dipole interaction leads to modify both the condensate and the superfluid fractions. We show that for a strong disorder strength the condensed fraction becomes larger than the superfluid fraction. We discuss the effect of the trapping potential on a disordered dipolar Bose in the regime of large number of particles.
Thu, 21
1. arXiv:1505.05370 [pdf, other]
Counterflow in a doubly superfluid mixture of Bosons and Fermions
F. Chevy
In this article, we calculate the friction between two counter-flowing bosonic and fermionic super-fluids. In the limit where the boson-boson and boson-fermion interactions can be treated within the mean-field approximation, we show that the force can be related to the dynamical structure factor of the fermionic component. Finally, we provide asymptotic expressions for weakly and strongly attractive fermions and show that the damping rate obeys simple scaling laws close to the critical velocity.
2. arXiv:1505.05318 [pdf, other]
Evolution of the Hofstadter butterfly in a tunable optical lattice
F. Yılmaz, F. Nur Ünal, M. Ö. Oktel
Recent advances in realizing artificial gauge fields on optical lattices promise experimental detection of topologically non-trivial energy spectra. Self-similar fractal energy structures generally known as Hofstadter butterflies depend sensitively on the geometry of the underlying lattice, as well as the applied magnetic field. The recent demonstration of an adjustable lattice geometry [L. Tarruell \textit{et al.}, Nature 483, 302--305 (2012)] presents a unique opportunity to study this dependence. In this paper, we calculate the Hofstadter butterflies that can be obtained in such an adjustable lattice and find three qualitatively different regimes. We show that the existence of Dirac points at zero magnetic field does not imply the topological equivalence of spectra at finite field. As the real-space structure evolves from the checkerboard lattice to the honeycomb lattice, two square lattice Hofstadter butterflies merge to form a honeycomb lattice butterfly. This merging is topologically non-trivial, as it is accomplished by sequential closings of gaps. Ensuing Chern number transfer between the bands can be probed with the adjustable lattice experiments. We also calculate the Chern numbers of the gaps for qualitatively different spectra and discuss the evolution of topological properties with underlying lattice geometry.
Wed, 20
1. arXiv:1505.05130 [pdf, other]
Dynamical thermalization of Bose-Einstein condensate in Bunimovich stadium
Leonardo Ermann, Eduardo Vergini, Dima L. Shepelyansky
We study numerically the wavefunction evolution of a Bose-Einstein condensate in a Bunimovich stadium billiard being governed by the Gross-Pitaevskii equation. We show that for a moderate nonlinearity, above a certain threshold, there is emergence of dynamical thermalization which leads to the Bose-Einstein probability distribution over the linear eigenmodes of the stadium. This distribution is drastically different from the energy equipartition over oscillator degrees of freedom which would lead to the ultra-violet catastrophe. We argue that this interesting phenomenon can be studied in cold atom experiments.
2. arXiv:1505.04820 [pdf, other]
Turning the BEC-BCS crossover into a transition by radiation
Y. Lemonik, I. L. Aleiner, B. L. Altshuler
We show that the Bardeen-Cooper-Schrieffer state (BCS) and the Bose-Einstein condensation (BEC) sides of the BCS-BEC crossover can be rigorously distinguished from each other by the extrema of the spectrum of the fermionic excitations. Moreover, we demonstrate that this formal distinction is realized as a non-equilibrium phase transition under radio frequency radiation. The BEC phase remains translationally invariant, whereas the BCS phase transforms into the supersolid phase. For a two-dimensional system this effect occurs at arbitrary small amplitude of the radiation field.
Tue, 19
1. arXiv:1505.04530 [pdf, other]
Impurity in a Bose-Einstein condensate and the Efimov effect
Jesper Levinsen, Meera M. Parish, Georg M. Bruun
We investigate the zero-temperature properties of an impurity particle interacting with a Bose-Einstein condensate (BEC), using a variational wavefunction that includes up to two Bogoliubov excitations of the BEC. This allows one to capture three-body Efimov physics, as well as to recover the first non-trivial terms in the weak-coupling expansion. We show that the energy and quasiparticle residue of the dressed impurity (polaron) are significantly lowered by three-body correlations, even for weak interactions where there is no Efimov trimer state in a vacuum. For increasing attraction between the impurity and the BEC, we observe a smooth crossover from atom to Efimov trimer, with a superposition of states near the Efimov resonance. We furthermore demonstrate that three-body loss does not prohibit the experimental observation of these effects. Our results thus suggest a route to realizing Efimov physics in a stable quantum many-body system for the first time.
Mon, 18 May
1. arXiv:1505.04080 [pdf, ps, other]
Establishing the Gauge Invariant Linear Response of Fermionic Superfluids with Pair Fluctuations: A Diagrammatic approach
Yan He, Hao Guo
We present a manifestly gauge invariant linear response theory for ultra-cold Fermi gases undergoing BCS-Bose-Einstein Condensation (BEC) crossover with pair fluctuation effect included, especially in the superfluid phase, by introducing an effective external electromagnetic (EM) field. For pure BCS-type superfluids, the gauge invariance of the linear response theory can be maintained by constructing a full external EM vertex by including the fluctuation of the order parameters in the same way as the the self-energy effect is included in the quasi-particle, therefore the Ward identity (WI) is satisfied. While for the Fermionic superfluids with pairing fluctuation effect included in the quasi-particle self-energy, the construction of a gauge invariant vertex is non-trivial, since in the broken symmetry phase the effect of Nambu-Goldstone modes (collective modes) intertwines with that of the pairing fluctuation. In this paper, we find that under a suitable diagrammatic representation, the construction of such vertex is greatly simplified, which allow us to build a WI-maintaining vertex with pseudogap effects included in the superfluid phase. We focus on the G0G t-matrix approach to the pair fluctuations, although our formalism should also works equally well for the G0G0 t-matrix theory.
2. arXiv:1505.04009 [pdf, other]
Chiral d-wave superfluid in periodically driven lattices
Shao-Liang Zhang, Li-Jun Lang, Qi Zhou
Chiral d-wave superfluid is a preliminary example of topological matters that intrinsically encodes interaction effects. It exhibits fascinating properties including a finite Chern number in the bulk and topologically protected edge states, which have been invoking physicists for decades. However, unlike s-wave superfluids prevalent in nature, its existence requires a strong interaction in the d-wave channel, a criterion that is difficult to access in ordinary systems. So far, such an unconventional superfluid has not been discovered in experiments. Here, we present a new principle for creating a two-dimensional chiral d-wave superfluid using periodically driven lattices. Due to an imprinted two-dimensional pseudospin-orbit coupling, where the sublattice index serves as the pseudospin, s-wave interaction between two hyperfine spin states naturally creates a chiral d-wave superfluid. This scheme also allows physicists to study the phase transition between the topologically distinct s- and d-wave superfluids by controlling the driving field or the particle density.
May 15
1. arXiv:1505.03753 [pdf, other]
Effective many-body parameters for atoms in non-separable Gaussian optical potentials
Michael L. Wall, Kaden R. A. Hazzard, A. M. Rey
Comments: 20 pages, 15 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We analyze the properties of particles trapped in three-dimensional potentials formed from superimposed Gaussian beams, fully taking into account effects of potential anharmonicity and non-separability. Although these effects are negligible in more conventional optical lattice experiments, they are essential for emerging ultracold atom developments. We focus in particular on two potentials utilized in current ultracold atom experiments: arrays of tightly focused optical tweezers and a one-dimensional optical lattice with transverse Gaussian confinement and highly excited transverse modes. Our main numerical tools are discrete variable representations (DVRs), which combine many favorable features of spectral and grid-based methods, such as the computational advantage of exponential convergence and the convenience of an analytical representation of Hamiltonian matrix elements. Optimizations, such as symmetry adaptations and variational methods built on top of DVR methods, are presented and their convergence properties discussed. We also present a quantitative analysis of the degree of non-separability of eigenstates, borrowing ideas from the theory of matrix product states (MPSs), leading to both conceptual and computational gains. Beyond developing numerical methodologies, we present results for construction of optimally localized Wannier functions and tunneling and interaction matrix elements in optical lattices and tweezers relevant for constructing effective models for many-body physics.
2. arXiv:1505.03646 [pdf, ps, other]
Phase diagram of a non-Abelian Aubry-André-Harper model with $p$-wave superfluidity
Jun Wang, Xia-Ji Liu, Gao Xianlong, Hui Hu
Comments: 7 pages, 6 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We theoretically study a one-dimensional quasi-periodic Fermi system with topological p-wave superfluidity, which can be deduced from a topologically non-trivial tight-binding model on the square lattice in a uniform magnetic field and subject to a non-Abelian gauge field. The system may be regarded a non-Abelian generalization of the well-known Aubry-Andr\'e-Harper model. We investigate its phase diagram as functions of the strength of the quasi-disorder and the amplitude of the p-wave order parameter, through a number of numerical investigations, including a multifractal analysis. There are four distinct phases separated by three critical lines, i.e., two phases with all extended wave-functions (I and IV), a topologically trivial phase (II) with all localized wave-functions and a critical phase (III) with all multifractal wave-functions. The phase I is related to the phase IV by duality. It also seems to be related to the phase II by duality. Our proposed phase diagram may be observable in current cold-atom experiments, in view of simulating non-Abelian gauge fields and topological insulators/superfluids with ultracold atoms.
3. arXiv:1505.03519 [pdf, ps, other]
Fermionic Luttinger liquids from a microscopic perspective
Manuel Valiente, Lawrence G. Phillips, Nikolaj T. Zinner, Patrik Ohberg
Comments: 25 pages, 3 figures. Comments, suggestions about missing references, etc. are welcomeSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We consider interacting one-dimensional, spinless Fermi gases, whose low-energy properties are described by Luttinger liquid theory. We perform a systematic, in-depth analysis of the relation between the macroscopic, phenomenological parameters of Luttinger liquid effective field theory, and the microscopic interactions of the Fermi gas. In particular, we begin by explaining how to model effective interactions in one dimension, which we then apply to the main forward scattering channel -- the interbranch collisions -- common to these systems. We renormalise the corresponding interbranch phenomenological constants in favour of scattering phase shifts. Interestingly, our renormalisation procedure shows (i) how Luttinger's model arises in a completely natural way -- and not as a convenient approximation -- from Tomonaga's model, and (ii) the reasons behind the interbranch coupling constant remaining unrenormalised in Luttinger's model. We then consider the so-called intrabranch processes, whose phenomenological coupling constant is known to be fixed by charge conservation, but whose microscopic origin is not well understood. We show that, contrary to general belief and common sense, the intrabranch interactions appearing in Luttinger liquid theory do not correspond to an intrabranch scattering channel, nor an energy shift due to intrabranch interactions, in the microscopic theory. Instead, they are due to interbranch processes. We finally apply our results to a particular example of an exactly solvable model, namely the fermionic dual to the Lieb-Liniger model in the Tonks-Girardeau and super-Tonks-Girardeau regimes.
May 14
1. arXiv:1505.03146 [pdf, other]
Topological phases with long-range interactions
Zhe-Xuan Gong, Mohammad F. Maghrebi, Anzi Hu, Michael L. Wall, Michael Foss-Feig, Alexey V. Gorshkov
Comments: Supplementary material included
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
Topological phases of matter are primarily studied in quantum many-body systems with short-range interactions. Whether various topological phases can survive in the presence of long-range interactions, however, is largely unknown. Here we show that a paradigmatic example of a symmetry-protected topological phase, the Haldane phase of an antiferromagnetic spin-1 chain, surprisingly remains intact in the presence of arbitrarily slowly decaying power-law interactions. The influence of long-range interactions on the topological order is largely quantitative, and we expect similar results for more general systems. Our conclusions are based on large-scale matrix-product-state simulations and two complementary effective-field-theory calculations. The striking agreement between the numerical and analytical results rules out finite-size effects. The topological phase considered here should be experimentally observable in a recently developed trapped-ion quantum simulator.
May 13
1. arXiv:1505.03126 [pdf, other]
On solving the quantum many-body problem
Thomas Schweigler, Valentin Kasper, Sebastian Erne, Bernhard Rauer, Tim Langen, Thomas Gasenzer, Jürgen Berges, Jörg Schmiedmayer
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realize the quantum sine-Gordon/massive Thirring models relevant for a wide variety of disciplines from particle to condensed-matter physics. From measured interference patterns we extract phase correlation functions and analyze if, and under which conditions, the higher-order correlation functions factorize into lower ones. This allows us to characterize the essential features of the model solely from our experimental measurements, detecting the relevant quasiparticles, their interactions and the topologically distinct vacua. Our method provides comprehensive insights into a non-trivial quantum field theory and establishes a general method to analyze quantum many-body systems through experiments.
2. arXiv:1505.03099 [pdf, other]
Bilayer fractional quantum Hall states with ultracold dysprosium
Norman Y. Yao, Steven D. Bennett, Chris R. Laumann, Benjamin L. Lev, Alexey V. Gorshkov
Comments: 11 pages, 7 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We show how dipolar interactions between dysprosium atoms in an optical lattice can be used to obtain fractional quantum Hall states. In our approach, dysprosium atoms are trapped one atom per site in a deep optical lattice with negligible tunneling. Microwave and spatially dependent optical dressing fields are used to define an effective spin-1/2 or spin-1 degree of freedom in each atom. Thinking of spin-1/2 particles as hardcore bosons, dipole-dipole interactions give rise to boson hopping, topological flat bands with Chern number 1, and the \nu = 1/2 Laughlin state. Thinking of spin-1 particles as two-component hardcore bosons, dipole-dipole interactions again give rise to boson hopping, topological flat bands with Chern number 2, and the bilayer Halperin (2,2,1) state. By adjusting the optical fields, we find a phase diagram, in which the (2,2,1) state competes with superfluidity. Generalizations to solid-state magnetic dipoles are discussed.
3. arXiv:1505.02800 [pdf, other]
Synthetic Helical Liquids with Ultracold Atoms in Optical Lattices
J. C. Budich, C. Laflamme, F. Tschirsich, S. Montangero, P. Zoller
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We develop a new platform for the synthetic realization of helical Tomonaga Luttinger liquids (HTLLs) with ultracold fermionic atoms in one-dimensional optical lattices. The HTLL is a strongly correlated metallic state where spin polarization and propagation direction of the itinerant particles are locked to each other. We propose an unconventional one-dimensional Fermi-Hubbard model which, at quarter filling, resembles the HTLL in the long wavelength limit, as we demonstrate with a combination of analytical (bosonization) and numerical (density matrix renormalization group) methods. An experimentally feasible scheme is provided for the realization of this model with ultracold fermionic atoms in optical lattices. Finally, we discuss how the robustness of the HTLL against backscattering and imperfections, well known from its realization at the edge of a two-dimensional topological insulators, is reflected in the present synthetic scenario.
May 12
1. arXiv:1505.02733 [pdf, other]
Effects of anisotropy in simple lattice geometries on many-body properties of ultracold fermions in optical lattices
Anna Golubeva, Andrii Sotnikov, Walter Hofstetter
Comments: 10 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We study the effects of anisotropic hopping amplitudes on quantum phases of ultracold fermions in optical lattices described by the repulsive Fermi-Hubbard model. In particular, using dynamical mean-field theory (DMFT) we investigate the dimensional crossover between the isotropic square and the isotropic cubic lattice. We analyze the phase transition from the antiferromagnetic to the paramagnetic state and observe a significant change in the critical temperature: Depending on the interaction strength, the anisotropy can lead to both a suppression or increase. We also investigate the localization properties of the system, such as the compressibility and double occupancy. Using the local density approximation in combination with DMFT we conclude that density profiles can be used to detect the mentioned anisotropy-driven transitions.
2. arXiv:1505.02657 [pdf, other]
Multiphoton excitations of quantum gases in driven optical lattices
M. Weinberg, C. Ölschläger, C. Sträter, S. Prelle, A. Eckardt, K. Sengstock, J. Simonet
Subjects: Quantum Gases (cond-mat.quant-gas)
We report on the observation of multiphoton absorption processes for quantum gases in shaken light crystals. Periodic inertial forcing, induced by a spatial motion of the lattice potential, drives multiphoton interband excitations of up to the 9th order. The occurrence of such excitation features is systematically investigated with respect to the potential depth and the driving amplitude. Ab initio calculations of resonance positions as well as numerical evaluation of their strengths exhibit a good agreement with experimental data. In addition our findings set the stage for reaching novel phases of quantum matter by tailoring appropriate driving schemes.
3. arXiv:1505.02526 [pdf, other]
Universal Properties of a Strongly Interacting Fermi Gas at $p$-wave Resonance
Zhenhua Yu, Joseph H. Thywissen, Shizhong Zhang
Comments: 5 pages, 1 figureSubjects: Quantum Gases (cond-mat.quant-gas)
In this letter, we investigate the properties of a strongly interacting spinless Fermi gas close to a p-wave resonance. We show that the universal properties at p-wave resonance are captured by two contacts, which are related respectively to the variation of energy to the p-wave scattering volume v and the effective range R in the two adiabatic theorems derived. We show how the two contacts determine the leading and sub-leading asymptotic behavior of the momentum distribution (∼1/k2 and ∼1/k4) and how they can be measured experimentally by radio-frequency, Bragg and photo-association spectroscopies. Finally, we determine the temperature dependences of the two contacts at high temperature via the virial expansion.
4. arXiv:1505.02242 [pdf, ps, other]
Landau instability and mobility edges of the interacting one-dimensional Bose gas in weak random potentials
Alexander Yu. Cherny, Jean-Sébastien Caux, Joachim Brand
Comments: 8 pages, 4 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
Expansion of a trapped Bose gas over weak random potentials has been used to test theoretical predictions of Anderson localization for ultracold atoms. We here study how Anderson localization is influenced by interparticle interactions during the expansion of a one-dimensional gas. Extended potentials generated by speckle patterns with a finite correlation length are specifically considered. It is shown that the onset of localization is provided by a generalized Landau instability of the one-dimensional gas. We perform a quantitative analysis of the Landau instability based on the dynamic structure factor of the integrable Lieb-Liniger model. In the limits of weak and strong interactions between bosons, the results obtained for the initial stages of expansion which are accessible to our method are consistent with the existence of a mobility edge for a single particle moving in a random potential with a finite correlation length.
May 11
1. arXiv:1505.02123 [pdf, other]
Observation of the Berezinskii-Kosterlitz-Thouless phase transition in an ultracold Fermi gas
P. A. Murthy, I. Boettcher, L. Bayha, M. Holzmann, D. Kedar, M. Neidig, M. G. Ries, A. N. Wenz, G. Zürn, S. Jochim
Comments: 9 pages, 5 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
We experimentally investigate the first-order correlation function of a trapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a transition to a low-temperature superfluid phase with algebraically decaying correlations. We show that the spatial coherence of the entire trapped system can be characterized by a single temperature-dependent exponent. We find the exponent at the transition to be independent of the interaction strength. This suggests that the phase transitions both in the bosonic regime and the strongly interacting crossover regime are of Berezinskii-Kosterlitz-Thouless-type and lie within the same universality class. On the bosonic side of the crossover, our data is well-described by Quantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly interacting regime, we observe a superfluid phase which is significantly influenced by the fermionic nature of the constituent particles.
2. arXiv:1505.01875 [pdf, ps, other]
Superfluid to normal fluid phase transition in the Bose gas trapped in two dimensional optical lattices at finite temperature
M. O. C. Pires, E. J. V. de Passos
Subjects: Quantum Gases (cond-mat.quant-gas)
We develop the Hartree-Fock-Bogoliubov theory at finite temperature for Bose gas trapped in the two dimensional optical lattices. The on-site energy is considered low enough that the gas presents superfluid properties. We obtain the condensate density as function of the temperature neglecting the anomalous density in the thermodynamics equations. The condensate fraction provide two critical temperature. Below the temperature TC1 there is one condensate fraction. Above two possible fractions merger up to the critical temperature TC2. Then the gas provides an first order transition at temperature above TC2 where the condensate fraction is null. We resume by a finite-temperature phase diagram where can be identify three domains: the normal fluid, the superfluid and the superfluid with two possible condensate fractions.
3. arXiv:1505.01906 [pdf, ps, other]
Symmetry and the critical phase of the two-bath spin-boson model: Ground-state properties
Nengji Zhou, Lipeng Chen, Dazhi Xu, Vladimir Chernyak, Yang Zhao
Comments: 18 pages, 26 figures, to appear in PRBSubjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
A generalized trial wave function termed as the "multi-D1 Ansatz" has been developed to study the ground state of the spin-boson model with simultaneous diagonal and off-diagonal coupling in the sub-Ohmic regime. Ground-state properties including the energy and the spin polarization are investigated, and the results are consistent with those from the exact diagonalization and density matrix renormalization group approaches for the cases involving two oscillators and two baths described by a continuous spectral density function. Breakdown of the rotational and parity symmetries along the continuous quantum phase transition separating the localized phase from the critical phase has been uncovered. Moreover, the phase boundary is determined accurately with the corresponding symmetry parameters of the rotational and parity symmetries. A critical value of the spectral exponent s* = 0.49(1) is predicted in the weak coupling limit, which is in agreement with the mean-field prediction of 1/2, but much smaller than the earlier literature estimate of 0.75(1).
May 8
arXiv:1505.01491 [pdf, other]
Lattice assisted spectroscopy: a generalized scanning tunnelling microscope for ultra-cold atoms
Adrian Kantian, Ulrich Schollwöck, Thierry Giamarchi
Comments: 4 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We show that the possibility to address and image single sites of an optical lattice, now an experimental reality, allows to measure the frequency-resolved local particle and hole spectra of a wide variety of one- and two-dimensional systems of lattice-confined strongly correlated ultracold atoms. Combining perturbation theory and time-dependent DMRG, we validate this scheme of lattice-assisted spectroscopy (LAS) on several example systems, such as the 1D superfluid and Mott insulator, with and without a parabolic trap, and finally on edge states of the bosonic Su-Schrieffer-Heeger model. We also highlight extensions of our basic scheme to obtain an even wider variety of interesting and important frequency resolved spectra.
May 5
arXiv:1505.00722 [pdf, other]
Competing exotic quantum phases of spin-$1/2$ ultra-cold lattice bosons with extended spin interactions
Chia-Chen Chang, Valéry G. Rousseau, Richard T. Scalettar, George G. Batrouni
Comments: 11 pages, 10 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
Advances in pure optical trapping techniques now allow the creation of degenerate Bose gases with internal degrees of freedom. Systems such as ${}^{87}$Rb, $^{39}$K or ${}^{23}$Na in the $F=1$ hyperfine state offer an ideal platform for studying the interplay of superfluidity and quantum magnetism. Motivated by the experimental developments, we study ground state phases of a two-component Bose gas loaded on an optical lattice. The system is described effectively by the Bose-Hubbard Hamiltonian with onsite and near neighbor spin-spin interactions. An important feature of our investigation is the inclusion of interconversion (spin flip) terms between the two species. Using mean-field theory and quantum Monte Carlo simulations, we map out the phase diagram of the system. A rich variety of phases is identified, including antiferromagnetic (AF) Mott insulators, ferromagnetic and AF superfluids.
arXiv:1505.00665 [pdf, other]
Hamiltonian tomography for quantum many-body systems with arbitrary couplings
Sheng-Tao Wang, Dong-Ling Deng, Lu-Ming Duan
Comments: 9 pages, 4 figures, including supplemental material
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
Characterization of qubit couplings in many-body quantum systems is essential for benchmarking quantum computation and simulation. We propose a tomographic measurement scheme to determine all the coupling terms in a general many-body Hamiltonian with arbitrary long-range interaction. Different from quantum process tomography, our scheme is fully scalable with the number of qubits as the required rounds of measurements increase only linearly with the number of coupling terms in the Hamiltonian. The scheme makes use of synchronized dynamical decoupling pulses to simplify the many-body dynamics so that the unknown parameters in the Hamiltonian can be retrieved one by one. We simulate the performance of the scheme under the influence of various pulse errors and show that it is robust to typical noise and experimental imperfections.
May 4
arXiv:1505.00166 [pdf, ps, other]
Capture Dynamics of Ultracold Atoms in the Presence of an Impurity Ion
J. M. Schurer, A. Negretti, P. Schmelcher
Comments: 14 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Following the sudden creation of a single ion in a quasi one-dimensional trapped ultracold ensemble of bosonic atoms, the major part of the atoms is captured in the vicinity of the ion, while the remaining fraction is emitted towards the outer regions of the trap. Subsequently, the two energy scales stemming from the trapping potential and the atom-ion interaction give rise to two major density oscillations. While the first one corresponds to a dipole oscillation, the second one results from a coherent superposition of an atom-ion bound and a trap state which causes spatial coherence and population transfer between the two density fractions. Induced by the dynamical build-up of correlations, this second oscillation exhibits a collapse and revival behavior. We apply the ab initio multiconfiguration time-dependent Hartree method for bosons to explore the nonequilibrium quantum dynamics and analyze it via a cluster expansion approach. The latter is adapted to bosonic systems of fixed particle number which provides us with a thorough understanding of the complicated many-body processes.
27 Apr
1. **arXiv:1504.06411** [**pdf**, **ps**, **other**]
Non-equilibrium quasi-long-range order of driven random field O(N) model
Taiki Haga
2. **arXiv:1504.06564** [**pdf**, **ps**, **other**]
Spontaneous increase of magnetic flux and chiral-current reversal in bosonic ladders: Swimming against the tide
S. Greschner, M. Piraud, F. Heidrich-Meisner, I. P. McCulloch, U. Schollwöck, T. Vekua
3. **arXiv:1504.06581** [**pdf**, **other**]
Quantum optical lattices for emergent many-body phases of ultracold atoms
Santiago F. Caballero-Benitez, Igor B. Mekhov
28 Apr
1. **arXiv:1504.06620** [**pdf**, **other**]
Matrix Product State Representation of Non-Abelian Quasiholes
Yang-Le Wu, B. Estienne, N. Regnault, B. Andrei Bernevig
2.**arXiv:1504.06623** [**pdf**, **other**]
Fractional Chern Insulators in Harper-Hofstadter Bands with Higher Chern Number
Gunnar Möller, Nigel R. Cooper
3. **arXiv:1504.06769** [**pdf**, **other**]
Fibonacci Optical Lattices for Tunable Quantum Quasicrystals
Kevin Singh, David M. Weld
4. **arXiv:1504.06819** [**pdf**, **other**]
Topological Kondo insulator. Exact results
Igor N. Karnaukhov, Igor O. Slieptsov
5. **arXiv:1504.06872** [**pdf**, **other**]
Total correlations of the diagonal ensemble herald the many-body localization transition
J. Goold, S. R. Clark, C.Gogolin, J. Eisert, A. Scardicchio, A. Silva
6.**arXiv:1504.07143** [**pdf**, **other**]
Fractional Wigner crystal in the helical Luttinger liquid
N. Traverso Ziani, F. Crépin, B. Trauzettel
7. **arXiv:1504.07185** [**pdf**, **other**]
Quantum geometry and stability of the fractional quantum Hall effect in the Hofstadter model
David Bauer, T. S. Jackson, Rahul Roy
29 Apr
1. **arXiv:1504.07370** [**pdf**, **ps**, **other**]
Multicriticality, Metastability, and Roton Feature in Bose-Einstein Condensates with Three-Dimensional Spin-Orbit Coupling
Renyuan Liao, Oleksander Fialko, Joachim Brand, Ulrich Zulicke
2. **arXiv:1504.07258** [**pdf**, **other**]
Statistical translation invariance protects a topological insulator from interactions
A. Milsted, L. Seabra, I. C. Fulga, C. W. J. Beenakker, E. Cobanera
3.**arXiv:1504.07340** [**pdf**, **other**]
Observation of coherent back-scattering and its dynamics in a transverse 2D photonic disorder : from weak to strong localization
Julien Armijo, Raphaël Allio
4.**arXiv:1504.07370** [**pdf**, **ps**, **other**]
Multicriticality, Metastability, and Roton Feature in Bose-Einstein Condensates with Three-Dimensional Spin-Orbit Coupling
Renyuan Liao, Oleksander Fialko, Joachim Brand, Ulrich Zulicke
5.**arXiv:1504.07408** [**pdf**, **ps**, **other**]
Topological superconductivity in Dirac semimetals
Shingo Kobayashi, Masatoshi Sato
30 Apr
1. **arXiv:1504.07934** [**pdf**, **other**]
Polymer crystals in Rydberg quantum gases with competing attractive and repulsive interactions
Zhihao Lan, Jiří Minář, Emanuele Levi, Weibin Li, Igor Lesanovsky
2. **arXiv:1504.07701** [**pdf**, **other**]
Compression of Correlation Matrices and an Efficient Method for Forming Matrix Product States of Fermionic Gaussian States
Matthew T. Fishman, Steven R. White
3. **arXiv:1504.07762** [**pdf**, **ps**, **other**]
Collective modes of a harmonically trapped one-dimensional Bose gas: the effects of finite particle number and nonzero temperature
Xiao-Long Chen, Yun Li, Hui Hu
1 May
1. **arXiv:1504.07993** [**pdf**, **other**]
Higgs Mechanism and Anomalous Hall Effect in Three-Dimensional Topological Superconductors
Flavio S. Nogueira, Asle Sudbo, Ilya Eremin
2. **arXiv:1504.08019** [**pdf**, **ps**, **other**]
Supersymmetric waves in Bose-Fermi mixtures
Barry Bradlyn, Andrey Gromov
3. **arXiv:1504.08036** [**pdf**, **ps**, **other**]
Monte Carlo simulations of the kagome lattice with magnetic dipolar interactions
M. S. Holden, M. L. Plumer, I. Saika-Voivod, B. W. Southern
4. **arXiv:1504.08314** [**pdf**, **other**]
Temperature-induced spontaneous time-reversal symmetry breaking on the honeycomb lattice
Wei Liu, Alexander Punnoose
