Jun 2015

Jun 1-Jun 5 Haiyuan Zou, Jun 8-Jun 12 Ahmet Keles, Jun 15-Jun 19, Xuguang Yue, Jun 22-Jun 26, Max, Jun 29-July 3 Bo Liu

July 3
1. arXiv:1507.00470 [pdf, other]
Persistent bright solitons in sign-indefinite coupled nonlinear Schrodinger equations with a time-dependent harmonic trap
R. Radha, P. S. Vinayagam, J. B. Sudharsan, Boris. A. Malomed
We introduce a model based on a system of coupled nonlinear Schrodinger (NLS) equations with opposite signs infront of the kinetic and gradient terms in the two equations. It also includes time-dependent nonlinearity coefficients and a parabolic expulsive potential. By means of a gauge transformation, we demonstrate that, with a special choice of the time dependence of the trap, the system gives rise to persistent solitons. Exact single and two-soliton analytical solutions and their stability are corroborated by numerical simulations. In particular, the exact solutions exhibit inelastic collisions between solitons.


July 2
1. arXiv:1507.00318 [pdf, ps, other]
Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein condensate
Yan Li, Chunlei Qu, Yongsheng Zhang, Chuanwei Zhang
Synthetic spin-orbit (SO) coupling, an important ingredient for quantum simulation of many exotic condensed matter physics, has recently attracted considerable attention. The static and dynamic properties of a SO coupled Bose-Einstein condensate (BEC) have been extensively studied in both theory and experiment. Here we numerically investigate the generation and propagation of a \textit{dynamical} spin-density wave (SDW) in a SO coupled BEC using a fast moving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to the barrier's velocity while varies slightly with the barrier's peak potential or width. We qualitatively explain the generation of SDW by considering a rectangular barrier in a one dimensional system. Our results may motivate future experimental and theoretical investigations of rich dynamics in the SO coupled BEC induced by a moving barrier.


July 1

1. arXiv:1506.08983 (cross-list from cond-mat.str-el) [pdf, ps, other]
Non-equilibrium properties of a pumped-decaying Bose-condensed electron-hole gas in the BCS-BEC crossover region
Ryo Hanai, Peter B. Littlewood, Yoji Ohashi
We theoretically investigate a Bose-condensed exciton gas out of equilibrium. Within the framework of the combined BCS-Leggett strong-coupling theory with the non-equilibrium Keldysh formalism, we show how the Bose-Einstein condensation (BEC) of excitons is suppressed to eventually disappear, when the system is in the non-equilibrium steady state. The supply of electrons and holes from the bath is shown to induce quasi-particle excitations, leading to the partial occupation of the upper branch of Bogoliubov single-particle excitation spectrum. We also discuss how this quasi-particle induction is related to the suppression of exciton BEC, as well as the stability of the steady state.




Jun 30
1. arXiv:1506.08461 [pdf, other]
Chiral currents in one-dimensional fractional quantum Hall states
Eyal Cornfeld, Eran Sela

We study bosonic and fermionic quantum two-leg ladders with orbital magnetic flux. In such systems, the ratio, ν, of particle density to magnetic flux shapes the phase-space, as in quantum Hall effects. In fermionic (bosonic) ladders, when ν equals one over an odd (even) i integer, Laughlin fractional quantum Hall (FQH) states are stabilized for sufficiently long ranged repulsive interactions. As a signature of these fractional states, we find a unique dependence of the chiral currents on particle density and on magnetic flux. This dependence is characterized by the fractional filling factor ν, and forms a stringent test for the realization of FQH states in ladders, using either numerical simulations or future ultracold atom experiments. The two-leg model is equivalent to a single spinful chain with spin-orbit interactions and a Zeeman magnetic field, and results can thus be directly borrowed from one model to the other.



Jun 19
1. arXiv:1506.05609 [pdf, other]
Beyond the Hubbard bands in strongly correlated lattice bosons
Hugo U. R. Strand, Martin Eckstein, Philipp Werner
Comments: 8 pages, 3 figures, including supplemental material
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We investigate features in the single particle spectral function beyond the Hubbard bands in the strongly correlated normal phase of the Bose-Hubbard model. There are two distinct classes of additional peaks generated by the bosonic statistics. The first type is thermally activated Hubbard "side bands" with the same physical origin as the zero temperature Hubbard bands but generated by excitations from thermally activated local occupation number states. The second class are two-particle fluctuation resonances driven by the lattice dynamics. In the unity filling Mott insulator this takes the form of a localized triplon combined with a dispersing holon. Both types of resonances also manifest themselves in the structure factor and the interaction modulation spectra obtained from non-equilibrium bosonic dynamical mean-field theory calculations. Our findings explain experimental lattice modulation and Bragg spectroscopy results, and predict a strong temperature dependence of the first side-band, thereby opening the door to precise thermometry of strongly correlated lattice Bosons.

2. arXiv:1506.05455 (cross-list from cond-mat.dis-nn) [pdf, other]
Dynamical many-body localization in an integrable model
Aydin Cem Keser, Sriram Ganeshan, Gil Refael, Victor Galitski
Comments: 5 pages, 2 figuresSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)
We investigate dynamical many-body localization and delocalization in an integrable system of periodically-kicked, interacting linear rotors. The Hamiltonian we investigate is linear in momentum, and its Floquet evolution operator is analytically tractable for arbitrary interaction strengths. One of the hallmarks of this model is that depending on certain parameters, it manifest both localization and delocalization in momentum space. We explicitly show that, for this model, the energy being bounded at long times is not a sufficient condition for dynamical localization. Besides integrals of motion associated to the integrability, this model manifests additional integrals of motion, which are the exclusive consequence of dynamical many-body localization. We also propose an experimental scheme, involving voltage-biased Josephson junctions, to realize such many-body kicked models.

Jun 18
1. arXiv:1506.05221 [pdf, other]
Emergence of chaotic scattering in ultracold Er and Dy
T. Maier, H. Kadau, M. Schmitt, M. Wenzel, I. Ferrier-Barbut, T. Pfau, A. Frisch, S. Baier, K. Aikawa, L. Chomaz, M. J. Mark, F. Ferlaino, C. Makrides, E. Tiesinga, A. Petrov, S. Kotochigova
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)

We show that for ultracold magnetic lanthanide atoms chaotic scattering emerges due to a combination of anisotropic interaction potentials and Zeeman coupling under an external magnetic field. This scattering is studied in a collaborative experimental and theoretical effort for both dysprosium and erbium. We present extensive measurements of their dense magnetic Feshbach resonance spectra, analyze their statistical properties, and compare to predictions from a random-matrix-theory inspired model. Furthermore, theoretical coupled-channels simulations of the molecular Hamiltonian at zero magnetic field show that short-ranged anisotropic interactions are sufficiently strong that weakly-bound diatomic levels form overlapping, uncoupled chaotic series that when combined are randomly distributed. The Zeeman interaction shifts and couples these levels, leading to a Feshbach spectrum of zero-energy bound states with nearest-neighbor spacings that changes from randomly to chaotically distributed for increasing magnetic field.

2.arXiv:1506.05302 [pdf, ps, other]
Probing a quantum gas with single Rydberg atoms
Huan Nguyen, Tara Cubel Liebisch, Michael Schlagmüller, Graham Lochead, Karl M. Westphal, Robert Löw, Sebastian Hofferberth, Tilman Pfau
Subjects: Atomic Physics (physics.atom-ph)
We present a novel spectroscopic method for probing the \insitu~density of quantum gases. We exploit the density-dependent energy shift of highly excited {Rydberg} states, which is of the order 10\MHz\,/\,1E14\,cm-3 for \rubidium~for triplet s-wave scattering. The energy shift combined with a density gradient can be used to localize Rydberg atoms in density shells with a spatial resolution less than optical wavelengths, as demonstrated by scanning the excitation laser spatially across the density distribution. We use this Rydberg spectroscopy to measure the mean density addressed by the Rydberg excitation lasers, and to monitor the phase transition from a thermal gas to a Bose-Einstein condensate (BEC).


Jun 17
1. arXiv:1506.04761 [pdf, other]
PT invariant Weyl semimetals in gauge symmetric systems
L. Lepori, I. C. Fulga, A. Trombettoni, M. Burrello
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)

Weyl semimetals typically appear in systems in which either time-reversal (T) or inversion (P) symmetry are broken. We show that these topological states of matter can also arise in fermionic systems with gauge potentials preserving both T and P. The role of the gauge symmetry in the formation of Weyl points is discussed for both Abelian and non-Abelian gauge potentials. Focusing on a U(2) symmetric system in a cubic lattice, we show that double-Weyl points and Fermi arcs appear as an effect of gauge invariance. A simultaneous breaking of both gauge and time-reversal symmetry brings the P T invariant system into a usual Weyl semimetal with inversion symmetry

2. arXiv:1506.04895 (cross-list from cond-mat.stat-mech) [pdf, ps, other]
Bose-Einstein condensation and critical behavior of two-component bosonic gases
Giacomo Ceccarelli, Jacopo Nespolo, Andrea Pelissetto, Ettore Vicari
Comments: 13 pagesSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas)
We study Bose-Einstein condensation (BEC) in three-dimensional two-component bosonic gases, characterizing the universal behaviors of the critical modes arising at the BEC transitions. For this purpose, we use field-theoretical (FT) renormalization-group (RG) methods and perform mean-field and numerical calculations. The FT RG analysis is based on the Landau-Ginzburg-Wilson Phi4 theory with two complex scalar fields which has the same symmetry as the bosonic system. In particular, for identical bosons with exchange Z_2,e symmetry, coupled by effective density-density interactions, the global symmetry is Z_2e X U(1) X U(1). At the BEC transition it may break into Z_2,e X Z_2 X Z_2 when both components condense simultaneously, or to U(1) X Z_2 when only one component condenses. This implies different universality classes for the corresponding critical behaviors. Numerical simulations of the two-component Bose-Hubbard model in the hard-core limit support the RG prediction: when both components condense simultaneously, the critical behavior is controlled by a decoupled XY fixed point, with unusual slowly-decaying scaling corrections arising from the on-site inter-species interaction.


Jun 16
1. arXiv:1506.04556 [pdf, ps, other]
Excitation band topology and edge matter waves in Bose-Einstein condensates in optical lattices
Shunsuke Furukawa, Masahito Ueda
Comments: 25 pages, 9 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We show that Bogoliubov excitations in Bose-Einstein condensates in optical lattices can support chiral edge modes originating from nontrivial bulk band topology. To be specific, we analyze a Bose-Hubbard extension of the Haldane model, which can be realized with recently developed techniques of manipulating honeycomb optical lattices. The topological properties of Bloch bands known for the noninteracting case are smoothly carried over to Bogoliubov excitation bands for the interacting case. We show that the parameter ranges displaying topological bands extend with increasing the Hubbard interaction or the particle density. With sharp boundaries, chiral edge modes appear in the gap between topological excitation bands. We demonstrate that by coherently transferring a portion of a condensate into an edge mode, a density wave is formed along the edge due to an interference with the background condensate. This offers a unique method of detecting an edge mode through a macroscopic quantum phenomenon.

2. arXiv:1506.04539 [pdf, other]
Extended Bose Hubbard model in a shaken optical lattice
Jiao Miao
Comments: 6 pages, 6 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
We study an extended Bose-Hubbard model with next-nearest-neighbor (NNN) hopping in a shaken optical lattice. We show how mean-field phase diagram evolves with the changing of NNN hopping amplitude t2, which can be easily tuned via shaking amplitude. As t2increases, a Z2-symmetry-breaking superfluid (Z2SF) phase emerges at the bottom of the Mott lobs. The tricritical points between normal superfluid, Z2SF, and Mott insulator (MI) phases are identified. We further demonstrate the tricritical point can be tuned to the tip of the Mott lobe, in which case a new critical behavior has been predicted. Within random-phase approximation, excitation spectra in the three phases are obtained, which indicate how the phase transitions occur.

3. arXiv:1506.04346 [pdf, ps, other]
Bosons with long range interactions on two-leg ladders in artificial magnetic fields
Stefan S. Natu
Comments: 11 pages, 4 figures. Comments are welcomeSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Motivated by experiments exploring the physics of neutral atoms in artificial magnetic fields, we study the ground state of bosons interacting with long range dipolar interactions on a two-leg ladder. Using two complimentary variational approaches, valid for weak interactions, we find rich physics driven by the long range forces. Generically, long range interactions tend to destroy the Meissner phase in favor of modulated density wave phases. Nearest neighbor interactions produce a novel interleg charge density wave phase, where the total density remains uniform, but the density on each leg of the ladder is modulating in space, out-of-phase with one another. At weak magnetic fields, next nearest neighbor interactions lead to a fully modulated biased ladder phase, where all the particles are on one leg of the ladder, and the density is modulating in space. This state simultaneously breaks Z2 reflection symmetry and U(1) symmetry associated with translation in real space. For values of the flux near ϕ=π, we find that a switching effect occurs for arbitrarily weak interactions, where the density modulates in space, but the chiral current changes sign on every plaquette. Arbitrarily weak attractive interactions along the rungs destroy the Meissner phase completely, in favor of a modulated density wave phase. Varying magnetic field produces a cascade of first order transitions between modulated density wave states with different wave-vectors, which manifests itself as discrete jumps in the chiral current. Polarizing the dipoles along the ladder direction yields a region of phase space where a stable biased ladder phase occurs even at arbitrarily weak magnetic fields. We discuss the experimental consequences of our work, in particular, how the interleg charge density wave can manifest itself in recent experiments on bosons in synthetic dimensions.


4. arXiv:1506.04169 [pdf, other]

One-dimensional ultracold atomic gases: impact of the effective range on integrability
Tom Kristensen (LPTMC), Ludovic Pricoupenko (LPTMC)
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

The one-dimensional one-component Bose and Fermi gases are considered in a regime of large effective range. We focus our study on the three-body problem, which is at the heart of the integra-bility issue. For fermions, the vicinity of the integrability is characterized by large deviations with respect to the predictions of the Bethe ansatz. For the consistency of the contact model, it appears essential to take into account the contact of three particles.

5. arXiv:1506.04528 (cross-list from cond-mat.stat-mech) [pdf, other]

Aging in isolated quantum systems after a critical quench: exact results
Anna Maraga, Alessio Chiocchetta, Aditi Mitra, Andrea Gambassi
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)




The non-equilibrium dynamics of an isolated quantum system after a sudden quench to a dynamical critical point is expected to be characterized by scaling and universal exponents due to the absence of time scales. We explore these features for a quench of the parameters of a Hamiltonian with O(N) symmetry, starting from a ground state in the disordered phase. In the limit of infinite N, the exponents and scaling forms of the relevant two-time correlation functions can be calculated exactly. Our analytical predictions are confirmed by the numerical solution of the corresponding equations. Moreover, we find that the same scaling functions, yet with different exponents, also describe the coarsening dynamics for quenches below the dynamical critical point.



6. arXiv:1506.04419 (cross-list from physics.atom-ph) [pdf, other]
Rapid production of uniformly-filled arrays of neutral atoms
Brian J. Lester, Niclas Luick, Adam M. Kaufman, Collin M. Reynolds, Cindy A. Regal
Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We demonstrate rapid loading of a small array of optical tweezers with a single 87Rb atom per site. We find that loading efficiencies of up to 90% per tweezer are achievable in less than 170 ms for traps separated by more than 1.7μm. Interestingly, we find the load efficiency is affected by nearby traps and present the efficiency as a function of the spacing between two optical tweezers. This enhanced loading, combined with subsequent rearranging of filled sites, will enable the study of quantum many-body systems via quantum gas assembly.




Jun 15
1. arXiv:1506.04053 [pdf, other]
Fluctuational susceptibility of ultracold bosons in the vicinity of condensation
Arvid J. Kingl, D.M. Gangardt, Igor V. Lerner
Comments: 5 pages, 3 figures, 5 pages of Supplement
Subjects: Quantum Gases (cond-mat.quant-gas)

We study the behaviour of ultracold bosonic gas in the critical region above the Bose-Einstein condensation in the presence of an artificial magnetic field, Bart. We show that the condensate fluctuations above the critical temperature Tc cause the fluctuational susceptibility, χfl, of a uniform gas to have a stronger power-law divergence than in an analogous superconducting system. Measuring such a divergence opens new ways of exploring critical properties of the ultracold gas and an opportunity of an accurate determination of Tc. We describe a method of measuring χfl which requires a constant gradient in Bart and suggest a way of creating such a field in experiment.

2. arXiv:1506.04020 [pdf, other]
Ehrenfest Breakdown of the Mean-field Dynamics of Bose Gases
Xizhi Han, Biao Wu
Subjects: Quantum Gases (cond-mat.quant-gas)
The mean-field dynamics of a Bose gas is shown to break down at time τh=(c1/γ)lnN where γ is the Lyapunov exponent of the mean-field theory, N is the number of bosons, and c1 is a system-dependent constant. The breakdown time τh is essentially the Ehrenfest time that characterizes the breakdown of the correspondence between classical and quantum dynamics. This breakdown can be well described by the quantum fidelity defined for reduced density matrices. Our results are obtained with the formalism in particle-number phase space and are illustrated with a triple-well model. The logarithmic quantum-classical correspondence time may be verified experimentally with Bose-Einstein condensates.

3. arXiv:1506.03964 [pdf, other]
Berry Curvature of interacting bosons in a honeycomb lattice
Yun Li, Pinaki Sengupta, George G. Batrouni, Christian Miniatura, Benoît Grémaud
Comments: 10 pages, 11 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We consider soft-core bosons with onsite interaction loaded in the honeycomb lattice with different site energies for the two sublattices. Using both a mean-field approach and quantum Monte-Carlo simulations, we show that the topology of the honeycomb lattice results in a non-vanishing Berry curvature for the band structure of the single-particle excitations of the system. This Berry curvature induces an anomalous Hall effect. It is seen by studying the time evolution of a wavepacket, namely a superfluid ground state in a harmonic trap, subjected either to a constant force (Bloch oscillations) or to a sudden shift of the trap center.

4. arXiv:1506.03887 [pdf, other]

Spin-momentum coupled Bose-Einstein condensates with lattice band pseudospins
M. A. Khamehchi, Chunlei Qu, M. E. Mossman, Chuanwei Zhang, P. Engels
Comments: 6 pages, 5 figuresSubjects: Quantum Gases (cond-mat.quant-gas)

The quantum emulation of spin-momentum coupling (SMC), a crucial ingredient for the emergence of topological phases, is currently drawing considerable interest. In previous quantum gas experiments, typically two atomic hyperfine states were chosen as pseudospins. Here, we report the observation of a new kind of SMC achieved by loading a Bose-Einstein condensate (BEC) into periodically driven optical lattices. The s- and p-bands of a static lattice, which act as pseudospins, are coupled through an additional moving lattice which induces a momentum dependent coupling between the two pseudospins, resulting in s-p hybrid Floquet-Bloch bands. We investigate the band structures by measuring the quasimomentum of the BEC for different velocities and strengths of the moving lattice and compare our measurements to theoretical predictions. The realization of SMC with lattice bands as pseudospins paves the way for engineering novel quantum matter using hybrid orbital bands.

5. arXiv:1506.04005 (cross-list from physics.atom-ph) [pdf, other]
Could optical lattices be used to simulate real materials?
J.P. Hague, C. MacCormick
Subjects: Atomic Physics (physics.atom-ph); Materials Science (cond-mat.mtrl-sci); Quantum Gases (cond-mat.quant-gas); Computational Physics (physics.comp-ph)

With the aim of understanding whether it is possible to build a quantum simulator that can probe multiband effects, we make DFT calculations for a system of cold atoms/ions. These move in a 1/r periodic potential convoluted by resolution effects, which represent the closest form of optical lattice to the nuclear potential in materials, that could be generated with painted potentials or holograms. We demonstrate that while resolution effects in optical lattices affect bandstructures, the physics of the bands closest to the fermi surface is sufficiently similar to that in real materials that they could give useful insight into complex multi-band processes. We determine that decoherence effects are sufficiently small that they do not destroy multiband effects, however there are strict constraints on the temperature and strength of interactions in experimental systems. The interaction form investigated here is most appropriate for cold ions, since inter-ion potentials have a native 1/r form. While a scaling argument demonstrates that (with the exception of the lightest ions) cold ions in optical lattices have interactions that are too large to form direct material analogues at currently achievable temperatures, the technology for very low temperature cold ion systems is rapidly progressing, and the interactions between ions are sufficiently similar to those between electrons that we expect them to be useful as a tuneable system for comparison with ab-initio numerical techniques. On the other hand, interaction strengths and forms between Rydberg atoms or polar molecules can be tuned to the right magnitude. Owing to the way correlation between atoms is considered, the results here represent a best case for where 1/r interactions between atoms can be achieved. If such interactions can be achieved experimentally then detailed quantum simulator analogues of real materials might be constructed.

Jun 8-12
 arXiv:1506.03082 [pdf, ps, other]
Driven impurity in an ultracold 1D Bose gas with intermediate interaction strength
Claudio Castelnovo, Jean-Sébastien Caux, Steven H. Simon
Comments: (5 pages, 2 figures)
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We study a single impurity driven by a constant force through a 1D Bose gas using a Lieb-Liniger based approach. Our calculaton is exact in the interaction amongst the particles in the Bose gas, and is perturbative in the interaction between the gas and the impurity. In contrast to previous studies of this problem, we are able to handle arbitrary interaction strength for the Bose gas. We find very good agreement with recent experiments [Phys. Rev. Lett. 103, 150601 (2009)].

 arXiv:1506.03020 [pdf, ps, other]
Spontaneous formation and non-equilibrium dynamics of a soliton-shaped Bose-Einstein condensate in a trap
Oleg L. Berman, Roman Ya. Kezerashvili, German V. Kolmakov, Leonid M. Pomirchi
Comments: 14 pages, 7 figures
Journal-ref: Phys. Rev. E 91, 062901 (2015)
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Pattern Formation and Solitons (nlin.PS)

The Bose-stimulated self-organization of a quasi-two dimensional non-equilibrium Bose-Einstein condensate in an in-plane potential is proposed. We obtained the solution of the nonlinear, driven-dissipative Gross-Pitaevskii equation for a Bose-Einstein condensate trapped in an external asymmetric parabolic potential within the method of the spectral expansion. We found that, in sharp contrast to previous observations, the condensate can spontaneously acquire a soliton-like shape for spatially homogenous pumping. This condensate soliton performs oscillatory motion in a parabolic trap and, also, can spontaneously rotate. Stability of the condensate soliton in the spatially asymmetric trap is analyzed. In addition to the nonlinear dynamics of non-equilibrium Bose-Einstein condensates of ultra-cold atoms, our findings can be applied to the condensates of quantum well excitons and cavity polaritons in semiconductor heterostructure, and to the condensates of photons.

 arXiv:1506.02947 [pdf, other]
Laser-induced Kondo effect in ultracold alkaline-earth fermions
Masaya Nakagawa, Norio Kawakami
Comments: 9 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We demonstrate that laser excitations can coherently induce a novel Kondo effect in ultracold atoms in optical lattices. Using a model of alkaline-earth fermions with two orbitals, it is shown that the optically coupled two internal states are dynamically entangled to form the Kondo-singlet state, overcoming the heating effect due to the irradiation. Furthermore, a lack of SU($N$) symmetry in the optical coupling provides a peculiar feature in the Kondo effect, which results in spin-selective renormalization of effective masses. We also discuss effects of interorbital exchange interactions, and reveal that they induce novel crossover or reentrant behavior of the Kondo effect owing to control of the coupling anisotropy. The laser-induced Kondo effect is highly controllable by tuning the laser strength and the frequency, and thus offers a versatile platform to study the Kondo physics using ultracold atoms.

 arXiv:1506.02861 [pdf, ps, other]
Experimental realization of a two-dimensional synthetic spin-orbit coupling in ultracold Fermi gases
Lianghui Huang, Zengming Meng, Pengjun Wang, Peng Peng, Shao-Liang Zhang, Liangchao Chen, Donghao Li, Qi Zhou, Jing Zhang
Comments: 4 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas)

Spin-orbit coupling (SOC) is central to many physical phenomena, including fine structures of atomic spectra and quantum topological matters. Whereas SOC is in general fixed in a physical system, atom-laser interaction provides physicists a unique means to create and control synthetic SOC for ultracold atoms \cite{Dalibard}. Though significant experimental progresses have been made, a bottleneck in current studies is the lack of a two-dimensional (2D) synthetic SOC, which is crucial for realizing high-dimensional topological matters. Here, we report the experimental realization of 2D SOC in ultracold $^{40}$K Fermi gases using three lasers, each of which dresses one atomic hyperfine spin state. Through spin injection radio-frequency (rf) spectroscopy, we probe the spin-resolved energy dispersions of dressed atoms, and observe a highly controllable Dirac point created by the 2D SOC. Our work paves the way for exploring high-dimensional topological matters in ultracold atoms using Raman schemes.

arXiv:1506.02775 [pdf, ps, other]
Ground state phase diagram of twisted three-leg spin tube in magnetic field
Kouki Yonaga, Naokazu Shibata
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

We study the ground state phase diagram of the twisted three-leg spin tube in magnetic fields by the density matrix renormalization group (DMRG) method. The twisted spin tube is composed of triangular unit cells and possesses strong quantum fluctuations under geometrical frustration. We apply the sine square deformation method to remove the strong boundary effects and obtain smooth magnetization curves without steps of finite systems. With the analysis of the magnetization curves and correlation functions we determine the ground state phase diagram consisting of (a) a Tomonaga-Luttinger (TL) liquid characterized by spin-$\frac{3}{2}$ Heisenberg model, (b) 3-sublattice state named UUD with 1/3 magnetization and (c) TL-liquid of massless chirality with 1/3 magnetization plateau, (d) TL-liquid of massless spin mode with or without chirality quasi long-range order.

 arXiv:1506.02747 [pdf, other]
Do Composite Fermions Satisfy Luttinger's Theorem?
Ajit C. Balram, Csaba Tőke, J. K. Jain
Comments: 14 pages, 10 figures including supplemental material
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

While an ordinary Fermi sea is perturbatively robust to interactions, the paradigmatic composite-fermion (CF) Fermi sea arises as a non-perturbative consequence of emergent gauge fields in a system where there was no Fermi sea to begin with. A mean-field picture produces two Fermi seas, of composite fermions made from electrons or holes in the lowest Landau level, which appear to be topologically distinct and occupy different areas. We provide evidence that these are dual descriptions of the same state. We calculate the Fermi wave vector in a particle-hole symmetric theory confined to the lowest Landau level, and find our results to be generally consistent with the experimental results of Kamburov {\em et al.} [Phys. Rev. Lett. {\bf 113}, 196801 (2014)]. Our calculations suggest that the area of the CF Fermi sea may not strictly satisfy the Luttinger theorem.
Jun 5
arXiv:1506.01640 [pdf, other]
Concept of contact spectrum and its applications in atomic quantum Hall states
Ming-Yuan He, Shao-Liang Zhang, Hon Ming Chan, Qi Zhou
Comments: 8 pages, 1 figures
Subjects: Quantum Gases (cond-mat.quant-gas)

A unique feature of ultracold atoms is the separation of length scales, $r_0\ll k_F^{-1}$, where $k_F$ and $r_0$ are the Fermi momentum characterizing the average particle distance and the range of interaction between atoms respectively. For $s$-wave scattering, Shina Tan discovered that such diluteness leads to universal relations, all of which are governed by contact, among a wide range of thermodynamic quantities. Here, we show that the concept of contact can be generalized to an arbitrary partial-wave scattering. Contact of all partial-wave scatterings form a contact spectrum, which establishes universal thermodynamic relations with notable differences from those in the presence of $s$-wave scattering alone. Moreover, such a contact spectrum has an interesting connection with a special bipartite entanglement spectrum of atomic quantum Hall states, and enables an intrinsic probe of these highly correlated states using two-body short-ranged correlations.
Jun 4
arXiv:1506.01172 [pdf, other]
Equilibrium angular momentum and edge current in Bose-condensed cold atom systems with k-space Berry curvature
Xiao-Hui Li, Ting-Pong Choy, Tai-Kai Ng
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)

In this paper we study the properties of cold bosons in a two-dimensional optical lattice system where Bose-condensation occurs at a momentum point k with non-zero k-space Berry curvature. By combining results from both analytic and numerical approaches, we show that the boson system carries non-universal, temperature dependent equilibrium angular momentum and edge current at low temperatures.

Jun 3
arXiv:1506.00723 [pdf, other]
Current-Driven Motion of Magnetic Domain Wall with Many Bloch Lines
Junichi Iwasaki, Naoto Nagaosa
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)

The current-driven motion of a domain wall (DW) in a ferromagnet with many Bloch lines (BLs) via the spin transfer torque is studied theoretically. It is found that the motion of BLs changes the current-velocity ($j$-$v$) characteristic dramatically. Especially, the critical current density to overcome the pinning force is reduced by the factor of the Gilbert damping coefficient $\alpha$ even compared with that of a skyrmion. This is in sharp contrast to the case of magnetic field driven motion, where the existence of BLs reduces the mobility of the DW.
Jun 2
arXiv:1506.00364 [pdf, other]
Second-order response theory of radio-frequency spectroscopy for cold atoms
C. Berthod, M. Koehl, T. Giamarchi
Comments: 16 pages, 13 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We present a theoretical description of the radio-frequency (rf) spectroscopy of fermionic atomic gases, based on the second-order response theory at finite temperature. This approach takes into account the energy resolution due to the envelope of the rf pulse. For a non-interacting final state, the momentum- and energy-resolved rf intensity depends on the fermion spectral function and pulse envelope. The contributions due to interactions in the final state can be classified by means of diagrams. Using this formalism, as well as the local density approximation in two and three dimensions, we study the interplay of inhomogeneities and Hartree energy in forming the line shape of the rf signal. We show that the effects of inhomogeneities can be minimized by taking advantage of interactions in the final state, and we discuss the most relevant final-state effects at low temperature and density, in particular the effect of a finite lifetime.


Jun 1
arXiv:1505.08164 [pdf, ps, other]
Detecting $π$-phase superfluids with $p$-wave symmetry in a quasi-1D optical lattice
Bo Liu, Xiaopeng Li, Randall G. Hulet, W. Vincent Liu
Comments: 5 pages, 5 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We propose an experimental protocol to study p-wave superfluidity in a spin-polarized cold Fermi gas tuned by an s-wave Feshbach resonance. A crucial ingredient is to add a quasi-1D optical lattice and tune the fillings of two spins to the s and p band, respectively. The pairing order parameter is confirmed to inherit p-wave symmetry in its center-of-mass motion. We find that it can further develop into a state of unexpected π-phase modulation in a broad parameter regime. Measurable quantities are calculated, including time-of-flight distributions, radio-frequency spectra, and in situ phase-contrast imaging in an external trap. The π-phase p-wave superfluid is reminiscent of the π-state in superconductor-ferromagnet heterostructures but differs in symmetry and origin. If observed, it would represent another example of p-wave pairing, first discovered in He-3 liquids.