Feb 2015
Feb 2-Feb 6 Bo Liu & Max, Feb 9-Feb 13, Zhenyu Zhou & Jinlong Yu, Feb 16-Feb 20, Jiyao chen & Jianhui zhou, Feb 23-Feb 27, Haiyuan Zou & Ahmet Keles
Feb 27
arXiv:1502.07443 [pdf, other]
Gauge matters: Observing the vortex-nucleation transition in a Bose condensate
L. J. LeBlanc, K. Jiménez-García, R. A. Williams, M. C. Beeler, W. D. Phillips, I. B. Spielman
Comments: 5 pages, 4 figures + 2 pages supplementary data
Subjects: Quantum Gases (cond-mat.quant-gas)
The order parameter of a quantum-coherent many-body system can include a phase degree of freedom, which, in the presence of an electromagnetic field, depends on the choice of gauge. Because of the relationship between the phase gradient and the velocity, time-of-flight measurements reveal this gradient. Here, we make such measurements using initially trapped Bose-Einstein condensates (BECs) subject to an artificial magnetic field. Vortices are nucleated in the BEC for artificial field strengths above a critical value, which represents a structural phase transition. By comparing to superfluid-hydrodynamic and Gross-Pitaevskii calculations, we confirmed that the transition from the vortex-free state gives rise to a shear in the released BEC's spatial distribution, representing a macroscopic method to measure this transition, distinct from direct measurements of vortex entry. Shear is also affected by an artificial electric field accompanying the artificial magnetic field turn-off, which depends on the details of the physical mechanism creating the artificial fields, and implies a natural choice of gauge. Measurements of this kind offer opportunities for studying phase in less-well-understood quantum gas systems.
Feb 26
arXiv:1502.07091 [pdf, ps, other]
Tunable spin-orbit coupling synthesized with a modulating gradient magnetic field
Xinyu Luo, Lingna Wu, Jiyao Chen, Qing Guan, Kuiyi Gao, Zhi-Fang Xu, L. You, Ruquan Wang
Comments: 8 pages, 5 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We report the observation of tunable spin-orbit coupling (SOC) for ultracold $^{87}$Rb atoms in hyperfine spin-1 states. Different from most earlier experiments where atomic SOC of pseudo-spin-1/2 are synthesized with Raman coupling lasers, the scheme we demonstrate employs a gradient magnetic field (GMF) with ground state atoms and is immune to atomic spontaneous emission. The effect of the SOC is confirmed through the studies of: 1) the collective dipole oscillation of an atomic condensate in a harmonic trap after the synthesized SOC is abruptly turned on; and 2) the minimum energy state at a finite adiabatically adjusted momentum when the SOC strength is slowly ramped up. The coherence properties of the spinor condensates remain very good after interacting with modulating GMFs, which prompts the enthusiastic claim that our work provides a new repertoire for synthesized gauge fields aimed at quantum simulation studies with cold atoms.
Feb 25
arXiv:1406.6915 [pdf, other]
Echo spectroscopy of Anderson localization
T. Micklitz, C. A. Müller, A. Altland
Comments: 14 pages, 7 figures; published version
Journal-ref: Phys. Rev. B 91, 064203 (2015)
We propose a conceptually new framework to study the onset of Anderson localization in disordered systems. The idea is to expose waves propagating in a random scattering environment to a sequence of short dephasing pulses. The system responds through coherence peaks forming at specific echo times, each echo representing a particular process of quantum interference. We suggest a concrete realization for cold gases, where quantum interferences are observed in the momentum distribution of matter waves in a laser speckle potential. This defines a challenging, but arguably realistic framework promising to yield unprecedented insight into the mechanisms of Anderson localization.
arXiv:1502.06661 [pdf, other]
Fluctuating hydrodynamics for a discrete Gross-Pitaevskii equation: mapping to Kardar-Parisi-Zhang universality class
Manas Kulkarni, David A. Huse, Herbert Spohn
Comments: 6 pages, 2 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We show that several aspects of the low-temperature hydrodynamics of a discrete Gross-Pitaevskii equation (GPE) can be understood by mapping it to a nonlinear version of fluctuating hydrodynamics. This is achieved by first writing the GPE in a hydrodynamic form of a continuity and an Euler equation. Respecting conservation laws, dissipation and noise due to the system's chaos are added, thus giving us a nonlinear stochastic field theory in general and the Kardar-Parisi-Zhang (KPZ) equation in our particular case. This mapping to KPZ is benchmarked against exact Hamiltonian numerics on discrete GPE by investigating the non-zero temperature dynamical structure factor and its scaling form and exponent. Given the ubiquity of the Gross-Pitaevskii equation (a.k.a. nonlinear Schrodinger equation), ranging from nonlinear optics to cold gases, we expect this remarkable mapping to the KPZ equation to be of paramount importance and far reaching consequences.
Feb 24
arXiv:1502.06202 [pdf, ps, other]
Bosonic Kondo-Hubbard model
T. Flottat, F. Hébert, V. G. Rousseau, R. T. Scalettar, G. G. Batrouni
Subjects: Quantum Gases (cond-mat.quant-gas)
We study, using quantum Monte-Carlo simulations, the bosonic Kondo-Hubbard model in a two dimensional square lattice. We explore the phase diagram and analyse the mobility of particles and magnetic properties. At unit filling, we find that the transition from a paramagnetic Mott insulator to a ferromagnetic superfluid is first order. When the Kondo interaction, $V$, is increased, this transition becomes continuous. For double occupation per site, both phases are ferromagnetic and the transition is continuous. Multiband tight binding Hamiltonians can be realized in optical lattice experiments, which offer not only the possibility of tuning the different energy scales over wide ranges, but also the option of loading the system with either fermionic or bosonic atoms.
Feb 23
arXiv:1502.05960 [pdf, other]
Classical dipoles on the kagome lattice
Mykola Maksymenko, V. Ravi Chandra, Roderich Moessner
Comments: 9 pages, 8 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)
Motivated by recent developments in magnetic materials, frustrated nanoarrays and cold atomic systems, we investigate the behaviour of dipolar spins on the frustrated two-dimensional kagome lattice. By combining the Luttinger-Tisza approach, numerical energy minimization, spin-wave analysis and parallel tempering Monte-Carlo, we study long-range ordering and finite-temperature phase transitions for a Hamiltonian containing both dipolar and nearest-neighbor interactions. For both weak and moderate dipolar interactions, the system enters a three-sublattice long-range ordered state, with each triangle having vanishing dipole and quadrupole moments; while for dominating dipolar interactions we uncover ferrimagnetic three-sublattice order. These are also the ground states for XY spins. We discuss excitations of, as well as phase transitions into, these states. We find behaviour consistent with Ising criticality for the 120-degree state, while the ferrimagnetic state appears to be associated with drifting exponents. The celebrated flat band of zero-energy excitations of the kagome nearest-neighbour Heisenberg model is lifted to finite energies but acquires only minimal dispersion as dipolar interactions are added.
Feb 20
arXiv:1502.05414 [pdf, other]
Hall Viscosity and Momentum Transport in Lattice and Continuum Models of the Integer Quantum Hall Effect in Strong Magnetic Fields
Thomas I. Tuegel, Taylor L. Hughes
arXiv:1502.05404 [pdf, ps, other]
Particle-Hole Symmetry and the Composite Fermi Liquid
Maissam Barkeshli, Michael Mulligan, Matthew P. A. Fisher
Feb 19
arXiv:1502.05391 [pdf, other]
Non-Abelian phases in two-component $ν=2/3$ fractional quantum Hall states: Emergence of Fibonacci anyons
Zhao Liu, Abolhassan Vaezi, Kyungmin Lee, Eun-Ah Kim
arXiv:1502.05076 [pdf, ps, other]
Emergence of Non-Abelian Moore-Read state in double-layer bosonic Fractional quantum Hall system
W. Zhu, S. S. Gong, D. N. Sheng, L. Sheng
arXiv:1502.05047 [pdf, other]
Occupation of topological Floquet bands in open systems
Thomas Iadecola, Titus Neupert, Claudio Chamon
Feb 18
arXiv:1502.04886 [pdf, ps, other]
Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry
E. Kalesaki, C. Delerue, C. Morais Smith, W. Beugeling, G. Allan, D. Vanmaekelbergh
Comments: 12 pages, 12 figures
Journal-ref: Physical Review X 4, 011010 (2014)
arXiv:1502.04866 [pdf, other]
Exactly solvable 2D topological Kondo lattice model
Igor N. Karnaukhov, Igor O. Slieptsov
arXiv:1502.04704 [pdf, ps, other]
Memory matrix theory of magnetotransport in strange metals
Andrew Lucas, Subir Sachdev
Feb 17
arXiv:1502.04684 [pdf]
Discovery of Weyl semimetal TaAs
B. Q. Lv, H. M. Weng, B. B. Fu, X. P. Wang, H. Miao, J. Ma, P. Richard, X. C. Huang, L. X. Zhao, G. F. Chen, Z. Fang, X. Dai, T. Qian, H. Ding
Comments: 14 pages, 4 figures, see also theoretical paper on TaAs arXiv:1501.00060
arXiv:1502.04208 [pdf, other]
Anomalous charge pumping in a one-dimensional optical superlattice
Ran Wei, Erich J. Mueller
arXiv:1502.04126 [pdf, ps, other]
Topological central charge from Berry curvature: gravitational anomalies in trial wavefunctions for topological phases
Barry Bradlyn, N. Read
Feb 16
Feb 13
1. arXiv:1502.03483 [pdf, other]
Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells
F. Fedichkin, P. Andreakou, B. Jouault, M. Vladimirova, T. Guillet, C. Brimont, P. Valvin, T. Bretagnon, A. Dussaigne, N. Grandjean, P. Lefebvre
Comments: 11 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially- and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that increases linearly with exciton density, whereas the radiative recombination rate increases exponentially. Under continuous, localized excitation, we measure a continuous red shift of the emission, as excitons propagate away from the excitation spot. This shift corresponds to a steady-state gradient of exciton density, measured over several tens of micrometers. Time-resolved micro-photoluminescence experiments provide information on the dynamics of recombination and transport of dipolar excitons. We account for the ensemble of experimental results by solving the nonlinear drift-diffusion equation. Quantitative analysis suggests that in such structures, exciton propagation on the scale of 10 to 20 microns is mainly driven by diffusion, rather than by drift, due to the strong disorder and the presence of nonradiative defects. Secondary exciton creation, most probably by the intense higher-energy luminescence, guided along the sample plane, is shown to contribute to the exciton emission pattern on the scale up to 100 microns. The exciton propagation length is strongly temperature dependent, the emission being quenched beyond a critical distance governed by nonradiative recombination.====
Feb 12
1. arXiv:1502.03291 [pdf, ps, other]
Understanding many-body physics in one dimension from the Lieb-Liniger model
Y.-Z. Jiang, Y.-Y. Chen, X.-W. Guan
Comments: 15 figures, for the special issue "Precision measurement with ultracold atoms" published in Chinese Physics B, based on XWG's lectures
Subjects: Quantum Gases (cond-mat.quant-gas)
This article presents an elementary introduction on various aspects of the prototypical integrable model the Lieb-Liniger Bose gas ranging from the cooperative to the collective features of many-body phenomena [1]. In 1963 Lieb and Liniger first solved this quantum field theory many-body problem using the Bethe's hypothesis, i.e. a particular form of wave function introduced by Bethe in solving the one-dimensional Heisenberg model in 1931. Despite the Lieb-Liniger model is arguably the simplest exactly solvable model, it exhibits rich quantum many-body physics in terms of the aspects of mathematical integrability and physical universality. Moreover, the Yang-Yang grand canonical ensemble description for the model provides us with a deep understanding of quantum statistics, thermodynamics and quantum critical phenomena at the many-body physics level. Recently, such fundamental physics of this exactly solved model has been attracting growing interest in experiments. Since 2004, there have been more than 20 experimental papers that report novel observations of different physical aspects of the Lieb-Liniger model in the lab. So far the observed results to date are seen to be in excellent agreement with results obtained using the analysis of this simplest exactly solved model. Those experimental observations reveal the unique beauty of integrability.====
2. arXiv:1502.03214 [pdf, other]
Competing structures in 2D-trapped dipolar gases
Barbara Gränz, Sergey E. Korshunov, Vadim B. Geshkenbein, Gianni Blatter
Journal-ref: Phys. Rev. B 90, 060101(R) (2014)Subjects: Quantum Gases (cond-mat.quant-gas)
We study a system of dipolar molecules confined in a two-dimensional trap and subject to an optical square lattice. The repulsive long-range dipolar interaction D/r3 favors an equilateral triangular arrangement of the molecules, which competes against the square symmetry of the underlying optical lattice with lattice constant b and amplitude V. We find the minimal-energy states at the commensurate density n=1/b2 and establish the complete square-to-triangular transformation pathway of the lattice with decreasing V involving period-doubled, solitonic, and distorted-triangular configurations.
Feb 11
1. arXiv:1502.02664 (cross-list from cond-mat.mes-hall) [pdf, other]
Controlled Population of Floquet-Bloch States via Coupling to Bose and Fermi Baths
Karthik I. Seetharam, Charles-Edouard Bardyn, Netanel H. Lindner, Mark S. Rudner, Gil Refael
Comments: 24 pages, 7 figures; with appendices
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
External driving is emerging as a promising tool for exploring new phases in quantum systems. The intrinsically non-equilibrium states that result, however, are challenging to describe and control. We study the steady states of a periodically driven one-dimensional electronic system, including the effects of radiative recombination, electron-phonon interactions, and the coupling to an external fermionic reservoir. Using a kinetic equation for the populations of the Floquet eigenstates, we show that the steady-state distribution can be controlled using the momentum and energy relaxation pathways provided by the coupling to phonon and Fermi reservoirs. In order to utilize the latter, we propose to couple the system and reservoir via an energy filter which suppresses photon-assisted tunneling. Importantly, coupling to these reservoirs yields a steady state resembling a band insulator in the Floquet basis. The system exhibits incompressible behavior, while hosting a small density of excitations. We discuss transport signatures, and describe the regimes where insulating behavior is obtained. Our results give promise for realizing Floquet topological insulators.
Feb 10
1. arXiv:1502.02507 [pdf, ps, other]
Anderson localization and Mott insulator phase in the time domain
Krzysztof Sacha
Comments: 4 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)
Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. There is an intriguing question if solid state phenomena can be observed in the time domain. Here we show that wave-packets localized on resonant classical trajectories of periodically driven systems are ideal elements to realize Anderson localization or Mott insulator phase in the time domain. Uniform superpositions of the wave-packets form stationary states of a periodically driven particle. However, an additional perturbation that fluctuates in time results in disorder in time and Anderson localization effects emerge. Switching to many-particle systems we observe that depending on how strong particle interactions are, stationary states can be Bose-Einstein condensates or single Fock states where definite numbers of particles occupy the periodically evolving wave-packets. Our study shows that non-trivial crystal-like phenomena can be observed in the time domain.
2. arXiv:1502.02496 [pdf, other]
Visualizing edge states with an atomic Bose gas in the quantum Hall regime
B. K. Stuhl, H.-I Lu, L. M. Aycock, D. Genkina, I. B. Spielman
Comments: 14 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We engineered a two-dimensional magnetic lattice in an elongated strip geometry, with effective per-plaquette flux ~4/3 times the flux quanta. We imaged the localized edge and bulk states of atomic Bose-Einstein condensates in this strip, with single lattice-site resolution along the narrow direction. Further, we observed both the skipping orbits of excited atoms traveling down our system's edges, analogues to edge magnetoplasmons in 2-D electron systems, and a dynamical Hall effect for bulk excitations. Our lattice's long direction consisted of the sites of an optical lattice and its narrow direction consisted of the internal atomic spin states. Our technique has minimal heating, a feature that will be important for spectroscopic measurements of the Hofstadter butterfly and realizations of Laughlin's charge pump.====
3. arXiv:1502.02495 [pdf, other]
Observation of chiral edge states with neutral fermions in synthetic Hall ribbons
M. Mancini, G. Pagano, G. Cappellini, L. Livi, M. Rider, J. Catani, C. Sias, P. Zoller, M. Inguscio, M. Dalmonte, L. Fallani
Comments: 10 pages (6 + 4 supplementary material)
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, we detect the existence of the edge states, investigate the onset of chirality as a function of the bulk-edge coupling, and observe the edge-cyclotron orbits induced during a quench dynamics. The realization of fermionic chiral edge states is a fundamental achievement, which opens the door towards experiments including edge state interferometry and the study of non-Abelian anyons in atomic systems.====
Feb, 9
1. arXiv:1502.01817 [pdf, other]
Ultracold fermions in a cavity-induced artificial magnetic field
Corinna Kollath, Ferdinand Brennecke
We show how a fermionic quantum gas in an optical lattice and coupled to the field of an optical cavity can self-organize into a state in which the spontaneously emerging cavity field amplitude induces an artificial magnetic field. The fermions form either a chiral insulator or a chiral liquid carrying edge currents. The feedback mechanism via the cavity field enables robust and fast switching of the edge currents and the cavity output can be employed for non-destructive measurements of the atomic dynamics.
2. arXiv:1502.01858 (cross-list from physics.atom-ph) [pdf, other]
Sensitivity of ultracold atoms to quantized flux in a superconducting ring
P. Weiss, M. Knufinke, S. Bernon, D. Bothner, L. Sárkány, C. Zimmermann, R. Kleiner, D. Koelle, J. Fortágh, H. Hattermann
We report on the magnetic trapping of an ultracold ensemble of 87Rb atoms close to a superconducting ring prepared in different states of quantized magnetic flux. The niobium ring of 10 μm radius is prepared in a flux state nΦ0, with Φ0=h/2e the flux quantum and n varies between ±5. An atomic cloud of 250 nK temperature is positioned with a harmonic magnetic trapping potential at ∼18μm distance below the ring. The inhomogeneous magnetic field of the supercurrent in the ring contributes to the magnetic trapping potential of the cloud. The induced deformation of the magnetic trap impacts the shape of the cloud, the number of trapped atoms as well as the center-of-mass oscillation frequency of Bose-Einstein condensates. When the field applied during cooldown of the chip is varied, the change of these properties shows discrete steps that quantitatively match flux quantization.
Feb, 6
1.arXiv:1502.01469 [pdf, other]
Density functional theory for strongly-correlated bosonic and fermionic ultracold dipolar and ionic gases
F. Malet, A. Mirtschink, C. B. Mendl, J. Bjerlin, E. O. Karabulut, S. M. Reimann, Paola Gori-Giorgi
Comments: 5 pages, 2 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We introduce a density functional formalism to study the ground-state properties of strongly-correlated dipolar and ionic ultracold bosonic and fermionic gases, based on the self-consistent combination of the weak and the strong coupling limits. Contrary to conventional density functional approaches, our formalism does not require a previous calculation of the interacting homogeneous gas, and it is thus very suitable to treat systems with tunable long-range interactions. Due to its asymptotic exactness in the regime of strong correlation, the formalism works for systems in which standard mean-field theories fail.
2.arXiv:1502.01546 (cross-list from quant-ph) [pdf, ps, other]
Site-selective particle deposition in periodically driven quantum lattices
Thomas Wulf, Benno Liebchen, Peter Schmelcher
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
We demonstrate that a site-dependent driving of a periodic potential allows for the controlled manipulation of a quantum particle on length scales of the lattice spacing. Specifically we observe for distinct driving frequencies a near depletion of certain sites which is explained by a resonant mixing of the involved Floquet-Bloch modes occurring at these frequencies. Our results could be exploited as a scheme for a site-selective loading of e.g. ultracold atoms into an optical lattices.
Feb, 5
1. arXiv:1502.01310 [pdf, ps, other]
Correlations and synchronization in a Bose-Fermi mixture
Pablo Díaz, David Laroze, Boris A. Malomed
Comments: Journal of Physics B: Atomic, Molecular and Optical Physics, in press
Subjects: Quantum Gases (cond-mat.quant-gas)
We study a Bose-Fermi mixture within the framework of the mean-field theory, including three possible regimes for the fermionic species: fully polarized, BCS, and unitarity. Starting from the 3D description and using the variational approximation (VA), we derive 1D and 2D systems of equations, under the corresponding confining potentials. This method produces a pair of nonlinear Schr\"{o}dinger (NLS) equations coupled to algebraic equations for the transverse widths of the confined state. The equations incorporate interactions between atoms of the same species and between the species, assuming that the latter can be manipulated by means of the Feshbach resonance (FR). As an application, we explore spatial density correlations in the ground state (GS) between the species, concluding that they strongly depend on the sign and strength of the inter-species interaction. Also studied are the dynamics of the mixture in a vicinity of the GS and the corresponding spatiotemporal inter-species correlation. The correlations are strongly affected by the fermionic component, featuring the greatest variation in the unitary regime. Results produced by the VA are verified by comparison with full numerical solutions.
2 arXiv:1502.01041 [pdf, ps, other]
Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical Lattice
Stefan S. Natu, J. H. Pixley, S. Das Sarma
Comments: 12 pages, 6 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We demonstrate that a site-dependent driving of a periodic potential allows for the controlled manipulation of a quantum particle on length scales of the lattice spacing. Specifically we observe for distinct driving frequencies a near depletion of certain sites which is explained by a resonant mixing of the involved Floquet-Bloch modes occurring at these frequencies. Our results could be exploited as a scheme for a site-selective loading of e.g. ultracold atoms into an optical lattices.
Feb, 4
1. arXiv:1502.00960 [pdf, ps, other]
Nonequilibrium dynamics of an ultracold dipolar gas
Andrew Sykes, John Bohn
Journal-ref: Physical Review A 91, 013625 (2015)
Subjects: Quantum Gases (cond-mat.quant-gas)
We study the relaxation and damping dynamics of an ultracold, but not quantum degenerate, gas consisting of dipolar particles. These simulations are performed using a direct simulation Monte Carlo method and employing the highly anisotropic differential cross section of dipoles in the Wigner threshold regime. We find that both cross-dimensional relaxation and damping of breathing modes occur at rates that are strongly dependent on the orientation of the dipole moments relative to the trap axis. The relaxation simulations are in excellent agreement with recent experimental results in erbium. The results direct our interest toward a less explored regime in dipolar gases where interactions are dominated by collision processes rather than mean-field interactions.
Feb, 3
1. arXiv:1502.00489 [pdf, ps, other]
Carbon-dioxide-type Skyrmion controlled by spin-orbit coupling in atomic-molecular Bose-Einstein condensates
Chao-Fei Liu, Gediminas Juzeliunas, Wu-Ming Liu
Comments: 37 pages,5 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
The recent realization of spin-orbit (SO) coupling in Bose-Einstein condensates (BECs) provides a new platform for exploring nontrivial topological excitations. However, almost all the investigations on the SO coupled ultracold atoms deal with pure atomic BECs or bound pairs of fermionic atoms, and there is no study of combined atomic-molecular BECs affected by the SO coupling. Here, we propose and explore a way of creating a Rashba-Dresselhaus SO coupling in the atomic-molecular BECs by combining the spin dependent photoassociation and Raman coupling. We find that the SO coupling can control formation and distribution of topological spin textures, where two half-Skyrmions of molecular BECs can couple with one Skyrmion of atomic BECs to form a carbon-dioxide-type Skyrmion. In real experiments this kind of Skyrmions can be detected by measuring the vortices structures using the time-of-flight absorption imaging technique.
2. arXiv:1502.00431 [pdf, ps, other]
Evolution of Higgs mode in a Fermion Superfluid with Tunable Interactions
Boyang Liu, Hui Zhai, Shizhong Zhang
Comments: 5 figures, 9 pages, including supplementary material
Subjects: Quantum Gases (cond-mat.quant-gas)
In this letter we present a coherent picture for the evolution of Higgs mode in both neutral and charged s-wave fermion superfluids, as the strength of attractive interaction between fermions increases from the BCS to the BEC regime. In the case of neutral fermionic superfluid, such as ultracold fermions, the Higgs mode is pushed to higher energy while at the same time, gradually loses its spectral weight as interaction strength increases toward the BEC regime, because the system is further tuned away from Lorentz invariance. On the other hand, when damping is taken into account, Higgs mode is significantly broadened due to coupling to phase mode in the whole BEC-BCS crossover. In the charged case of electron superconductor, the Anderson-Higgs mechanism gaps out the phase mode and suppresses the coupling between the Higgs and the phase modes, and consequently, stabilizes the Higgs mode.
Feb, 2
1. arXiv:1501.07886 [pdf, ps, other]
Two-body correlations and natural orbital tomography in ultracold bosonic systems of well-defined parity
Sven Krönke, Peter Schmelcher
Subjects: Quantum Gases (cond-mat.quant-gas)
The relationship between natural orbitals, one-body coherences and two-body correlations is explored for bosonic many-body systems of well-defined parity with two occupied single-particle states. We show that the strength of local two-body correlations at the parity-symmetry center characterizes the number state distribution and controls the structure of non-local two-body correlations. A recipe for the experimental reconstruction of the natural orbital densities and quantum depletion is derived. These insights into the structure of the many-body wave-function are applied to the predicted quantum-fluctuations induced decay of dark solitons.
2. arXiv:1501.07849 [pdf, other]
Thermodynamics of the Bose-Hubbard model in a Bogoliubov+U theory
Dario Hügel, Lode Pollet
Comments: 6 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We derive the Bogoliubov+U formalism to study the thermodynamical properties of the Bose-Hubbard model. The framework can be viewed as the zero-frequency limit of bosonic dynamical mean-field theory (B-DMFT), but equally well as an extension of the mean-field decoupling approximation in which pair creation and annihilation of depleted particles is taken into account. The self-energy on the impurity site is treated variationally, minimizing the grand potential. The theory containing just 3 parameters that are determined self-consistently reproduces the T=0 phase diagrams of the 3d and 2d Bose-Hubbard model with an accuracy of 1% or better. The superfluid to normal transition at finite temperature is also reproduced well and only slightly less accurately than in B-DMFT.
