Dec+2017

= Dec 1-Dec 4 Max Arzamasovs, Dec 5-Dec 9 Xuguang Yue, Dec 10-Dec 14 Biao Huang, Dec 15-Dec 19 Haiyuan Zou, = = Dec 20-Dec 24 Zehan Li, Dec 25-Dec 29 Jiansong Pan, Dec 30- Dec 31 Ahmet Keles =

Dec 29
[|arXiv:1712.09847] (cross-list from cond-mat.str-el) [[|pdf], [|other]] Multi-particle instability in a spin-imbalanced Fermi gas [|T.M. Whitehead], [|G.J. Conduit] Comments: 11 pages, 6 figures, accepted for publication in Physical Review B  Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con Weak attractive interactions in a spin-imbalanced Fermi gas induce a multi-particle instability, binding multiple fermions together. The maximum binding energy per particle is achieved when the ratio of the number of up- and down-spin particles in the instability is equal to the ratio of the up- and down-spin densities of states in momentum at the Fermi surfaces, to utilize the variational freedom of all available momentum states. We derive this result using an analytical approach, and verify it using exact diagonalization. The multi-particle instability extends the Cooper pairing instability of balanced Fermi gases to the imbalanced case, and could form the basis of a many-body state, analogously to the construction of the Bardeen-Cooper-Schrieffer theory of superconductivity out of Cooper pairs.

 [|arXiv:1712.09524] (cross-list from quant-ph) [[|pdf], [|ps], [|other]] Soliton Diffusion as a Signature of Hawking Radiation in Bose-Einstein Condensates [|Chao Hang], [|Gregory Gabadadze], [|Guoxiang Huang] Comments: 5 pages, 3 figures  Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) We propose a scheme to detect analog Hawking radiation (HR) in an atomic Bose-Einstein condensate (BEC) through measuring the diffusion of a dark soliton. The HR is generated by changing the transverse trapping potential of the BEC to obtain a background flow, which is subsonic in downstream and supersonic in upstream, satisfying the condition of black hole horizon. When the system is in thermal equilibrium at Hawking temperature, a dark soliton is created in the upstream. Due to the influence of the HR, the motion of the dark soliton is similar to a Brownian particle and hence exhibits an apparent diffusion, which can be measured and be taken as a signal of the HR. Since the dark soliton is much "heavier" than Hawking quanta, its diffusion is much easier detectable than the Hawking quanta themselves.

Dec 27
[|arXiv:1712.08775] (cross-list from hep-th) [[|pdf], [|other]] Note on Green Function Formalism and Topological Invariants [|Yehao Zhou], [|Junyu Liu] Comments: 19 pages, 3 figures  Subjects: High Energy Physics - Theory (hep-th) ; Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Algebraic Topology (math.AT) It has been discovered previously that the topological order parameter could be identified from the topological data of the Green function, namely the (generalized) TKNN invariant in general dimensions, for both non-interacting and interacting systems. In this note, we show that this phenomena has a clear geometric derivation. This proposal could be regarded as an alternative proof for the identification of the corresponding topological invariant and topological order parameter.

[|arXiv:1712.09011] (cross-list from cond-mat.supr-con) [[|pdf], [|other]] Gapped topological Fulde-Ferrell-Larkin-Ovchinnikov superfluids with artificial gauge potential and weak interaction [|Yue-Xin Huang], [|Wei-Feng Zhuang], [|Zhen Zheng], [|Guang-Can Guo], [|Ming Gong] Comments: 6 pages, 4 figures  Subjects: Superconductivity (cond-mat.supr-con) ; Quantum Gases (cond-mat.quant-gas) The topological superfluids with Majorana zero modes have not yet been realized in ultracold atoms with Rashba spin-orbit coupling. Here we show that these phases can be realized with an artificial gauge potential, which can be regarded as a site-dependent rotating Zeeman field. This potential breaks the inversion symmetry and plays the same role as Rashba spin-orbit coupling. In the inverted bands, this model can open a proper parameter regime for topological superfluids. Strikingly, we find that the interaction near the Fermi surface is dominated by the dispersion scattering in the same band, thus can realize topological phase with much weaker attractive interaction, as compared with the model with Rashba spin-orbit coupling. We find a large regime for the gapped topological Fulde-Ferrell-Larkin-Ovchinnikov superfluids and unveil the phase diagram with mean-field theory, which should be credible in the weak interaction regime. In regarding the negligible heating effect in realizing this potential in alkaline and rare-earth atoms, our model has the potential to be the first system to realize the long-sought topological FFLO phase and the associated Majorana zero modes.

 [|arXiv:1712.08769] (cross-list from physics.optics) [[|pdf]] Bound states in the continuum in a two-dimensional PT-symmetric system [|Yaroslav V. Kartashov], [|Carles Milian], [|Vladimir V. Konotop], [|Lluis Torner] Comments: 4 pages, 4 figures, to appear in Optics Letters Subjects: Optics (physics.optics) ; Quantum Gases (cond-mat.quant-gas); Mathematical Physics (math-ph); Pattern Formation and Solitons (nlin.PS)We address a two-dimensional parity-time (PT)-symmetric structure built as a chain of waveguides, where all waveguides except for the central one are conservative, while the central one is divided into two halves with gain and losses. We show that such a system admits bound states in the continuum (BICs) whose properties vary drastically with the orientation of the line separating amplifying and absorbing domains, which sets the direction of internal energy flow. When the flow is perpendicular to the chain of the waveguides, narrow BICs emerge when the standard defect mode, which is initially located in the finite gap, collides with another mode in a standard symmetry breaking scenario and its propagation constant enters the continuous spectrum upon increase of the strength of gain/losses. In contrast, when the energy flow is parallel to the chain of the waveguides, the symmetry gets broken even for a small strength of the gain/losses. In that case, the most rapidly growing mode emerges inside the continuous spectrum and realizes a weakly localized BIC. All BICs found here are the most rapidly growing modes, therefore they can be excited from noisy inputs and, importantly, should dominate the beam dynamics in experiments.

Dec 25
[|arXiv:1712.08610] [[|pdf], [|other]] Droplet crystal ground states of a dipolar Bose gas [|D. Baillie], [|P. B. Blakie] Comments: 5+1 pages, 4 figures  Subjects: Quantum Gases (cond-mat.quant-gas) We show that the ground state of a dipolar Bose gas in a cylindrically symmetric harmonic trap has a rich phase diagram, including droplet crystal states in which a set of droplets arrange into a lattice pattern that breaks the rotational symmetry. An analytic model for small droplet crystals is developed and used to obtain a zero temperature phase diagram that is numerically validated. We show that in certain regimes a coherent low-density halo surrounds the droplet crystal giving rise to a novel phase with localized and extended features.

[|arXiv:1712.08426] [[|pdf], [|other]] Polarization of a Bose-Einstein Condensate of Photons in a Dye-Filled Microcavity [|S. Greveling], [|F. van der Laan], [|H. C. Jagers], [|D. van Oosten] Comments: 6 pages, 5 figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph) We measure the polarization of a photon gas in a dye-filled microcavity. The polarization is obtained by a single-shot measurement of the Stokes parameters. We find that the polarization of both the thermal cloud and the Bose-Einstein condensate of photons (phBEC) does not differ from shot to shot. In the case of the phBEC, we find that the polarization correlates with the polarization of the pump pulse. The polarization of the thermal cloud is independent of parameters varied in the experiment and is governed by a hidden anisotropy in the system.

[|arXiv:1712.08318] [[|pdf], [|ps], [|other]] Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: The Goldstone phonon and its Landau damping [|Peng Zou], [|Hui Hu], [|Xia-Ji Liu] Comments: 6 pages, 5 figures  Subjects: Quantum Gases (cond-mat.quant-gas) We develop a microscopic theory of dynamic structure factor to describe the Bogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly interacting Fermi gas at finite temperature. It is based on a density functional approach - the so-called superfluid local density approximation. The accuracy of the theory is quantitatively examined by comparing the theoretical predictions with the recent experimental measurements for the local dynamic structure factor of a nearly homogeneous unitary Fermi gas at low transferred momentum {[}S. Hoinka \textit{et al.}, Nat. Phys. \textbf{13}, 943 (2017){]}, without any free parameters. We calculate the dynamic structure factor as functions of temperature and transferred momentum, and determine the temperature evolution of the phonon damping rate, by considering the dominant decay process of the phonon mode via scatterings off fermionic quasiparticles. These predictions can be confronted with future Bragg scattering experiments on a unitary Fermi gas near the superfluid transition.

Dec 22
[|arXiv:1712.08020] [[|pdf], [|other]] Residual entropy and critical behavior of two interacting boson species in a double well [|Fabio Lingua], [|Andrea Richaud], [|Vittorio Penna] Comments: 18 pages, 9 figures  Subjects: Quantum Gases (cond-mat.quant-gas)  Motivated by the importance of entanglement and correlation indicators in the analysis of quantum systems, we study the equilibrium and the residual entropy in a two-species Bose Hubbard dimer when the spatial phase separation of the two species takes place. We consider both the zero and non-zero-temperature regime. We present different kinds of residual entropies (each one associated to a different way of partitioning the system), and we show that they strictly depend on the specific quantum phase characterizing the two species (supermixed, mixed or demixed) even at finite temperature. To provide a deeper physical insight into the zero-temperature scenario, we apply the fully-analytical variational approach based on su(2) coherent states and provide a considerbly good approximation of the entanglement entropy. Finally, we show that the effectiveness of residual entropy as a critical indicator at non-zero temperature is unchanged when considering a restricted combination of energy eigenstates.

Dec 21
[|arXiv:1711.07181] [[|pdf], [|ps], [|other]] A strongly interacting high partial wave Bose gas [|Juan Yao], [|Ran Qi], [|Pengfei Zhang] Subjects: Quantum Gases (cond-mat.quant-gas)  Motivated by recent experimental progress, we make an investigation of p- and d-wave resonant Bose gas. An explanation of the Nozi`eres and Schmitt-Rink (NSR) scheme in terms of two-channel model is provided. Different from the s-wave case, high partial wave interaction supports a quasibound state in the weak coupling regime. Within the NSR approximation, we study the equation of state, critical temperature and particle population distributions. We clarify the effect of the quasi-bound state on the phase diagram and the dimer production. A multi-critical point where normal phase, atomic superfluid phase and molecular superfluid phase meet is predicted within the phase diagram. We also show the occurrence of a resonant conversion between solitary atoms and dimers when temperature kBT approximates the quasi-bound energy.

Dec 19
[|arXiv:1712.06545] [[|pdf], [|ps], [|other]] Title: Frustrated superfluids in a non-Abelian flux Authors: [|Fadi Sun], [|Junsen Wang], [|Jinwu Ye], [|Youjin Deng] Comments: Revtex4-1, 12 pages, 8 figures Subjects: Quantum Gases (cond-mat.quant-gas) Abstract: We study possible superfluid states of the Rashba spin-orbit coupled (SOC) spinor bosons with the spin anisotropic interaction λ hopping in a square lattice. The frustrations from the non-abelian flux due to the SOC leads to novel spin-bond correlated superfluids. By using a recently developed systematic "order from quantum disorder" analysis, we not only determine the true quantum ground state, but also evaluate the mass gap in the spin sector at λ < 1, especially compute the the excitation spectrum of the Goldstone mode in the spin sector at λ = 1  which would be quadratic without the analysis. The analysis also leads to different critical exponents on the two sides of the 2nd order transition driven by a roton touchdown at <span class="mi" style="font-family: MathJax_Math; font-size: 19.2px;">λ <span class="mo" style="font-family: MathJax_Main; font-size: 19.2px;">= <span class="mn" style="font-family: MathJax_Main; font-size: 19.2px;">1. The intimate analogy at <span class="mi" style="font-family: MathJax_Math; font-size: 19.2px;">λ <span class="mo" style="font-family: MathJax_Main; font-size: 19.2px;">= <span class="mn" style="font-family: MathJax_Main; font-size: 19.2px;">1 with the charge neutral Goldstone mode in the pseudo-spin sector in the Bilayer quantum Hall systems at the total filling factor <span class="mi" style="font-family: MathJax_Math; font-size: 19.2px;">ν <span class="mi" style="font-family: MathJax_Math; font-size: 13.6px;">T <span class="mo" style="font-family: MathJax_Main; font-size: 19.2px;">= <span class="mn" style="font-family: MathJax_Main; font-size: 19.2px;">1  are stressed. The experimental implications and detections of these novel phenomena in cold atoms loaded on a optical lattice are presented.

[|arXiv:1712.06458] (cross-list from quant-ph) [[|pdf], [|other]] Title: Observing Fermion Pair Instability of the Sachdev-Ye-Kitaev Model on a Quantum Spin Simulator Authors: [|Zhihuang Luo], [|Yi-Zhuang You], [|Jun Li], [|Chao-Ming Jian], [|Dawei Lu], [|Cenke Xu], [|Bei Zeng], [|Raymond Laflamme] Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)

The Sachdev-Ye-Kitaev (SYK) model has become increasingly of great interest in studying exotic non-fermi liquid states without quasiparticle excitations, holography duality to Einstein gravity, and quantum chaos. However, the unnatural form of its Hamiltonian, including its strong randomness and fully nonlocal fermion interaction, makes its experimental investigation an intractable challenge. A promising solution to overcome this challenge is quantum simulation, whose role will be more pronounced particularly in the future when more qubits can be handled. We have enough control to demonstrate a first step towards quantum simulation of this system. We observed the fermion paring instability of the non-Fermi liquid state and the chaotic-nonchaotic transition at simulated temperatures, as was predicted by previous theory. These results demonstrate the feasibility of experimentally simulating the SYK model. It opens a new experimental avenue towards investigating the key features of non-Fermi liquid states, as well as the quantum chaotic systems and the AdS/CFT duality, thanks to the rich physics of the SYK model.

Dec 18
[|arXiv:1712.05588] [[|pdf], [|other]] Title: Dynamical quantum phase transitions in discrete time crystals Authors: [|Arkadiusz Kosior], [|Krzysztof Sacha] Comments: 6 pages, 3 figs Subjects: Quantum Gases (cond-mat.quant-gas) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph) Discrete time crystals are related to non-equilibrium dynamics of periodically driven quantum many-body systems where the discrete time translation symmetry of the Hamiltonian is spontaneously broken into another discrete symmetry. Recently, the concept of phase transitions has been extended to non-equilibrium dynamics of time-independent systems induced by a quantum quench, i.e. a sudden change of some parameter of the Hamiltonian. There, the return probability of a system to the ground state reveals singularities in time which are dubbed dynamical quantum phase transitions. We show that the quantum quench in a discrete time crystal leads to dynamical quantum phase transitions where the return probability of a periodically driven system to a Floquet eigenstate before the quench reveals singularities in time. It indicates that dynamical quantum phase transitions are not restricted to time-independent systems and can be also observed in systems that are periodically driven.

Dec 15
[|arXiv:1712.05111] [[|pdf], [|ps], [|other]] Title: Ground-state phases of a mixture of spin-1 and spin-2 Bose-Einstein condensates Authors: [|Naoki Irikura], [|Yujiro Eto], [|Takuya Hirano], [|Hiroki Saito] Comments: 10 pages, 11 figures Subjects: Quantum Gases (cond-mat.quant-gas) We investigate the ground-state phases of a mixture of spin-1 and spin-2 Bose-Einstein condensates at zero magnetic field. In addition to the intra-spin interactions, two spin-dependent interaction coefficients are introduced to describe the inter-spin interaction. We systematically explore the wide parameter space, and obtain phase diagrams containing a rich variety of phases. For example, there exists a phase in which the spin-1 and spin-2 vectors are tilted relative to each other breaking the axial symmetry.

Dec 11 =<span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: x-large;">Topological Mott Insulator with Bosonic Edge Modes in 1D Fermionic Superlattices = <span style="background-color: #ffffff; display: block; font-family: "Lucida Grande",helvetica,arial,verdana,sans-serif; font-size: medium;">[|Haiping Hu], [|Shu Chen], [|Tian-Sheng Zeng], [|Chuanwei Zhang] <span style="background-color: #ffffff; display: block; font-family: "Lucida Grande",helvetica,arial,verdana,sans-serif; font-size: small;">(Submitted on 11 Dec 2017) > We investigate topological phase transitions driven by interaction and identify a novel topological Mott insulator state in one-dimensional fermionic optical superlattices through numerical density matrix renormalization group (DMRG) method. Remarkably, the low-energy edge excitations change from spin-1/2 fermionic single-particle modes to spin-1 bosonic collective modes across the phase transition. Due to spin-charge separation, the low-energy theory is governed by an effective spin superexchange model, whereas the charge degree of freedom is fully gapped out. Such topological Mott state can be characterized by a spin Chern number and gapless magnon modes protected by a finite spin gap. The proposed experimental setup is simple and may pave the way for the experimental observation of exotic topological Mott states.

Dec 8
1. [|arXiv:1712.02628] (cross-list from cond-mat.dis-nn) [[|pdf], [|other]] Many-body localization of bosons in optical lattices [|Piotr Sierant], [|Jakub Zakrzewski] Comments: 16 interesting pages, comments welcome  Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn) ; Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We show that two bosonic systems directly realizable in optical lattices: Bose-Hubbard model with random interactions and Bose-Hubbard model with random on-site potential host many-body localized phase. Time evolution of initially prepared density wave states at sufficiently strong disorder reveals ergodicity breaking, whereas the close inspection of the intermediate regime suggests algebraic decay which may be attributed to subdiffusion (and Griffiths-like regions) in the studied systems. Starting with various initial states, we observe that the localization properties are energy-dependent which, together with statistical properties of energy spectrum, reveals an inverted many-body localization edge in both systems. The ergodicity breaking in the disordered Bose-Hubbard models is compared with the slowing-down of time evolution of the clean system at large interactions.

<span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">2. [|arXiv:1712.02727] (cross-list from quant-ph) [[|pdf], [|other]] Synthetic three-dimensional atomic structures assembled atom by atom [|Daniel Barredo], [|Vincent Lienhard], [|Sylvain de Léséleuc], [|Thierry Lahaye], [|Antoine Browaeys] Comments: 5 pages, 3 figures  Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We demonstrate the realization of large, fully loaded, arbitrarily-shaped three-dimensional arrays of single atoms. Using holographic methods and real-time, atom-by-atom, plane-by-plane assembly, we engineer atomic structures with up to 72 atoms separated by distances of a few micrometres. Our method allows for high average filling fractions and the unique possibility to obtain defect-free arrays with high repetition rates. These results find immediate application for the quantum simulation of spin Hamiltonians using Rydberg atoms in state-of-the-art platforms, and are very promising for quantum-information processing with neutral atoms.

Dec 7
1. [|arXiv:1712.02181] [[|pdf], [|other]] Collective modes of an imbalanced unitary Fermi gas [|Johannes Hofmann], [|Frédéric Chevy], [|Olga Goulko], [|Carlos Lobo] Comments: 8 pages, 3 figures  Subjects: Quantum Gases (cond-mat.quant-gas) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We study theoretically the collective mode spectrum of a strongly imbalanced two-component unitary Fermi gas in a cigar-shaped trap, where the minority species forms a gas of polarons. We describe the collective breathing mode of the gas in terms of the Fermi liquid kinetic equation taking collisions into account using the method of moments. Our results for the frequency and damping of the longitudinal in-phase breathing mode are in good quantitative agreement with an experiment by Nascimb\`ene et al. [Phys. Rev. Lett. 103, 170402 (2009)] and interpolate between a hydrodynamic and a collisionless regime as the polarization is increased. A separate out-of phase breathing mode, which for a collisionless gas is sensitive to the effective mass of the polaron, however, is strongly damped at finite temperature, whereas the experiment observes a well-defined oscillation.

<span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">2. [|arXiv:1712.01874] [[|pdf], [|other]] Parton theory of magnetic polarons: Mesonic resonances and signatures in dynamics [|Fabian Grusdt], [|Marton Kanasz-Nagy], [|Annabelle Bohrdt], [|Christie S. Chiu], [|Geoffrey Ji], [|Markus Greiner], [|Daniel Greif], [|Eugene Demler] Comments: 30 pages, 4 appendices, 26 figures Subjects: Quantum Gases (cond-mat.quant-gas) ; Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">When a mobile hole is moving in an anti-ferromagnet it distorts the surrounding Neel order and forms a magnetic polaron. Such interplay between hole motion and anti-ferromagnetism is believed to be at the heart of high-Tc superconductivity in cuprates. We study a single hole described by the t-Jz model with Ising interactions between the spins in 2D. This situation can be experimentally realized in quantum gas microscopes. When the hole hopping is much larger than couplings between the spins, we find strong evidence that magnetic polarons can be understood as bound states of two partons, a spinon and a holon carrying spin and charge quantum numbers respectively. We introduce a microscopic parton description which is benchmarked by comparison with results from advanced numerical simulations. Using this parton theory, we predict a series of excited states that are invisible in the spectral function and correspond to rotational excitations of the spinon-holon pair. This is reminiscent of mesonic resonances observed in high-energy physics, which can be understood as rotating quark antiquark pairs. We also apply the strong coupling parton theory to study far-from equilibrium dynamics of magnetic polarons observable in current experiments with ultracold atoms. Our work supports earlier ideas that partons in a confining phase of matter represent a useful paradigm in condensed-matter physics and in the context of high-Tc superconductivity. While direct observations of spinons and holons in real space are impossible in traditional solid-state experiments, quantum gas microscopes provide a new experimental toolbox. We show that, using this platform, direct observations of partons in and out-of equilibrium are possible. Extensions of our approach to the t-J model are also discussed. Our predictions in this case are relevant to current experiments with quantum gas microscopes for ultracold atoms.

3. [|arXiv:1712.01844] (cross-list from cond-mat.stat-mech) [[|pdf], [|other]] Information measures for a local quantum phase transition: Lattice fermions in a one-dimensional harmonic trap [|Yicheng Zhang], [|Lev Vidmar], [|Marcos Rigol]  Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Gases (cond-mat.quant-gas) We use quantum information measures to study the local quantum phase transition that occurs for trapped spinless fermions in one-dimensional lattices. We focus on the case of a harmonic confinement. The transition occurs upon increasing the characteristic density and results in the formation of a band insulating domain in the center of the trap. We show that the ground-state bipartite entanglement entropy can be used as an order parameter to characterize this local quantum phase transition. We also study excited eigenstates by calculating the average von Neumann and second Renyi eigenstate entanglement entropies, and compare the results to the thermodynamic entropy and the mutual information of thermal states at the same energy density. While at low temperatures we observe a linear increase of the thermodynamic entropy with temperature at all characteristic densities, the average eigenstate entanglement entropies behave strikingly different below and above the transition. They are linear in temperature below the transition but exhibit activated behavior above it. Hence, at nonvanishing energy densities above the ground state, the average eigenstate entanglement entropies carry fingerprints of the local quantum phase transition.

Dec 6
1. [|arXiv:1708.02704] (cross-list from physics.atom-ph) [[|pdf], [|other]] Dynamics of interacting fermions under spin-orbit coupling in an optical lattice clock [|S.L. Bromley], [|S. Kolkowitz], [|T. Bothwell], [|D. Kedar], [|A. Safavi-Naini], [|M.L. Wall], [|C. Salomon], [|A.M. Rey], [|J. Ye] Subjects: Atomic Physics (physics.atom-ph) ; Quantum Gases (cond-mat.quant-gas) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">Quantum statistics and symmetrization dictate that identical fermions do not interact via s-wave collisions. However, in the presence of spin-orbit coupling (SOC), fermions prepared in identical internal states with distinct momenta become distinguishable. The resulting strongly interacting system can exhibit exotic topological and pairing behaviors, many of which are yet to be observed in condensed matter systems. Ultracold atomic gases offer a promising pathway for simulating these rich phenomena. Two recent experiments reported the observation of single atom SOC in optical lattice clocks (OLCs) based on alkaline-earth atoms. In these works encoding the effective spin degree of freedom in the long-lived electronic clock states significantly reduced the detrimental effects of spontaneous emission and heating that have thus far hindered the study of interacting SOC with alkali atoms. Beyond first studies of interacting SOC with alkali atoms in a bulk gas and with two particles in a lattice, here we enter a new regime of many-body interacting SOC in an OLC. Using clock spectroscopy, we observe the precession of the collective magnetization and the emergence of spin locking effects arising from an interplay between p-wave and SOC-induced exchange interactions. The many-body dynamics are well captured by a collective XXZ spin model, which describes a broad class of condensed matter systems ranging from superconductors to quantum magnets. Furthermore, our work will aid in the design of next-generation OLCs by offering a route for avoiding the observed large density shifts caused by SOC-induced exchange interactions.

2. [|arXiv:1712.01560] (cross-list from quant-ph) [[|pdf], [|other]] Dynamics of non-equilibrium steady state quantum phase transitions [|Patrik Hedvall], [|Jonas Larson] Comments: 21 pages, 9 figures  Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">In this paper we address the question how the Kibble-Zurek mechanism, which describes the formation of topological defects in quantum systems subjected to a quench across a critical point, is generalized to the same scenario but for driven-dissipative quantum critical systems. In these out of equilibrium systems, the critical behavior is manifested in the steady states rather than in the ground states as in quantum critical models of closed systems. To give the generalization we need to establish what is meant by adiabaticity in open quantum systems. Another most crucial concept that we clarify is the characterization of non-adiabatic excitations. It is clear what these are for a Hamiltonian systems, but question is more subtle for driven-dissipative systems. In particular, the important observation is that the instantaneous steady states serve as reference states. From these the excitations can then be extracted by comparing the distance from the evolved state to the instantaneous steady state. With these issues resolved we demonstrate the applicability of the generalized Kibble-Zurek mechanism to an open Landau-Zener problem and show universal Kibble-Zurek scaling for an open transverse Ising model. Thus, our results support any assumption that non-equilibrium quantum critical behavior can be understood from universal features.

<span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">3. [|arXiv:1712.01538] [[|pdf], [|other]] Interaction-driven Coalescence of Two Impurities in a One-dimensional Bose Gas [|A. S. Dehkharghani], [|A. G. Volosniev], [|N. T. Zinner] Comments: 11 pages, 6 figures, comments are most welcome Subjects: Quantum Gases (cond-mat.quant-gas) ; Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We study the ground state of a one-dimensional (1D) trapped Bose gas with two mobile impurity particles. To investigate this set-up, we develop a variational procedure in which the coordinates of the impurity particles are slow-like variables. We validate our method using the exact results obtained for small systems. Then, we discuss energies and pair densities for systems that contain of the order of one hundred atoms. We show that bosonic non-interacting impurities cluster, in a way realizing a few-body analogue of the phase separation of two Bose gases. To explain the clustering, we calculate and discuss induced impurity-impurity potentials in a harmonic trap. Further, we compute the force between static impurities in a ring ({\it {\'a} la} the Casimir force), and contrast the two effective potentials: the one obtained from the mean-field approximation, and the one due to the one-phonon exchange. Our formalism and findings are important for understanding [beyond the polaron model] the physics of modern 1D cold-atom systems with more than one impurity. 4. [|arXiv:1712.01732] [[|pdf], [|other]] Tuning the relaxation dynamics of ultracold atoms with an optical cavity [|Ezequiel Rodríguez Chiacchio], [|Andreas Nunnenkamp]  Subjects: Quantum Gases (cond-mat.quant-gas) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph) We investigate the out-of-equilibrium dynamics of ultracold atoms trapped in an optical lattice and loaded into an optical resonator that is driven transversely. We derive an effective quantum master equation for weak atom-light coupling that can be brought into Lindblad form both in the bad and good cavity limits. In the so-called bad cavity regime, we find that the steady state is always that of infinite temperature, but that the relaxation dynamics can be highly non-trivial. For small hopping, the interplay between dissipation and strong interactions generally leads to anomalous diffusion in the space of atomic configurations. However, for a fine-tuned ratio of cavity-mediated and on-site interactions, we discover a limit featuring normal diffusion. In contrast, for large hopping and vanishing on-site interactions, the system can be described by a linear rate equation leading to an exponential approach of the infinite-temperature steady state. Finally, in the good cavity regime, we show that for vanishing on-site interactions, the system allows for optical pumping between momentum mode pairs enabling cavity cooling.

Dec 5
1. [|arXiv:1712.01212] [[|pdf], [|ps], [|other]] Bosonic Integer Quantum Hall States without Landau Levels on Square Lattice [|Wanli Liu], [|Zhiyu Dong], [|Zhihuan Dong], [|Chenrong Liu], [|Wei Yan], [|Yan Chen] Comments: 5 pages, 4 figures, 1 table  Subjects: Quantum Gases (cond-mat.quant-gas) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We study an interacting two-component hard-core bosons on square lattice for which, in the presence of staggered magnetic flux, the ground state is a bosonic integer quantum Hall (BIQH) state. Using a coupled-wire bosonization approach, we analytically show this model exhibits a BIQH state at total charge half filling associated with a symmetry-protected topological phase under <span class="MathJax" style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;"><span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">U <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">( <span class="mn" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">1 <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;"> charge conservation. These theoretical expectations are verified, using the infinite density matrix renormalization group method, by providing numerical evidences for: (i) a quantized Hall conductance <span class="MathJax" style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;"><span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">σ <span class="mi" style="font-family: MathJax_Math-italic; font-size: 12.217px; vertical-align: 0px;">xy <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">=± <span class="mn" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">2 <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">, and (ii) two counter-propagating gapless edge modes. Our model is a bosonic cousin of the fermionic Haldane model and serves as an additional case of analogy between bosonic and fermionic quantum Hall states.

2. [|arXiv:1712.01190] [[|pdf], [|other]] A Non-Perturbative Method to Compute Thermal Correlations in One-Dimensional Systems [|Stefan Beck], [|Igor E. Mazets], [|Thomas Schweigler] Comments: to be submitted to Phys. Rev. Lett., an extended version aimed for Phys. Rev. A is in preparation Subjects: Quantum Gases (cond-mat.quant-gas) ; Statistical Mechanics (cond-mat.stat-mech) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We develop a highly efficient method to numerically simulate thermal fluctuations and correlations in non-relativistic continuous bosonic one-dimensional systems. We start by noticing the equivalence of their description through the transfer matrix formalism and a Fokker-Planck equation for a distribution evolving in space. The corresponding stochastic differential (It\={o}) equation is very suitable for computer simulations, allowing the calculation of arbitrary correlation functions. As an illustration, we apply our method to the case of two tunnel-coupled quasicondensates of bosonic atoms.

3. [|arXiv:1712.00655] [[|pdf], [|other]] Dark state optical lattice with sub-wavelength spatial structure [|Yang Wang], [|Sarthak Subhankar], [|Przemyslaw Bienias], [|Mateusz Łącki], [|Tsz-Chun Tsui], [|Mikhail A. Baranov], [|Alexey V. Gorshkov], [|Peter Zoller], [|James V. Porto], [|Steven L. Rolston]  Comments: 5 pages, 4 figures, and supplementary material Subjects: Quantum Gases (cond-mat.quant-gas) <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;">We report on the experimental realization of a conservative optical lattice for cold atoms with sub-wavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a 1D array of ultra-narrow barriers with widths less than 10~nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice, and find good agreement with theoretical predictions. The observed lifetimes of atoms trapped in the lattice are as long as 60 ms, nearly <span class="MathJax" style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;"><span class="mn" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">10 <span class="mn" style="font-family: MathJax_Main; font-size: 12.217px; vertical-align: 0px;">5 <span style="background-color: #ffffff; font-family: &#39;Lucida Grande&#39;,helvetica,arial,verdana,sans-serif; font-size: 14.4px;"> times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimension and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with sub-wavelength spacings.