Feb+2017

= Feb 1-Feb 10 Biao Huang, Feb 11-Feb 20 Haiyuan Zou, Feb 21-Feb 28 Zehan Li =

= Feb 20 = [|arXiv:1702.05097] [ [|pdf], [|other] ] Spin Polaron in an Optical Lattice [|C. W. Duncan], [|F. F. Bellotti] , [|P. Öhberg] , [|N. T. Zinner] , [|M. Valiente]   Comments: 12 pages, 10 figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph) We investigate the Fermi polaron problem in a spin-1/2 Fermi gas in a one-dimensional optical lattice with strong contact interactions. While the charge degrees of freedom of the system are frozen, the resulting tight-binding Hamiltonian for the polaron's spin exhibits an intriguing structure that strongly depends on the filling factor of the lattice potential. This filling dependency also transfers to the nature of the interactions for the case of two polarons and the important spin balanced case. At low filling, and up until near unit filling, the single polaron Hamiltonian faithfully reproduces a single-band, quasi-homogeneous tight-binding problem. As the filling is increased and the second band of the single particle spectrum of the periodic potential is progressively filled, the polaron Hamiltonian, at low energies, describes a single particle trapped in a multi-well potential. Interestingly, once the first two bands are fully filled, the polaron Hamiltonian is a near-perfect realisation of the Su-Schrieffer-Heeger model. Our studies, which go well beyond the single-band approximation, that is, the Hubbard model, pave the way for the realisation of interacting one-dimensional models of condensed matter physics.

 [|arXiv:1702.05115] [ [|pdf], [|other] ] Lattice Genons [|Zhao Liu], [|Gunnar Möller] , [|Emil J. Bergholtz]   Comments: 4+5 pages, 4+6 figures, including an Appendix. Comments are very welcome Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Topological degeneracy is, together with fractionalization, the hallmark of topological order. While fractionalization has been demonstrated both theoretically and in laboratories leading to deep insights into our basic understanding of matter, there has been no corresponding success in tracking the evolution of ground-state degeneracy due to the lack of tractable microscopic models with arbitrarily tunable topology of space. In this work however, by computer simulations, we show that lattice versions of multicomponent fractional quantum Hall systems are novel playgrounds to fill this void. With wormhole-like defects that connect separated "universes" of different components, thus changing the global topology of space, we observe a nontrivial dependence of ground-state degeneracy on the number of defects, equivalent to adding exotic non-Abelian quasiparticles called "genons" proposed recently in terms of effective topological field theory. We identify a number of different lattice genons in both Abelian and non-Abelian phases, with quantum dimensions exceeding those of fundamental quasiparticles in the host states, and provide a promising platform to study their intriguing behavior.

= Feb 17 = =  [|arXiv:1702.04735] [ [|pdf], [|ps] , [|other] ]  = Fulde-Ferrell-Larkin-Ovchinnikov state to Topologic Superfluidity Transition in Bilayer Spin-orbit Coupled Degenerate Fermi Gas [|Liang-Liang Wang], [|Qing Sun] , [|W.-M. Liu] , [|G. Juzeliünas] , [|An-Chun Ji]   Comments: 9 pages, 6 figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph) = = = = Recently a scheme has been proposed for generating the 2D Rashba-type spin-orbit coupling (SOC) for ultracold atomic bosons in a bilayer geometry [S.-W. Su et al, Phys. Rev. A 93, 053630 (2016)]. Here we investigate the superfluidity properties of a degenerate Fermi gas affected by the SOC in such a bilayer system. We demonstrate that a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state appears in the regime of small to moderate atom-light coupling. In contrast to the ordinary SOC, the FFLO state emerges in the bilayer system without adding any external fields or spin polarization. As the atom-light coupling increases, the system can transit from the FFLO state to a topological superfluid state. These findings are also confirmed by the BdG simulations with a weak harmonic trap added.

 [|arXiv:1702.04892] [ [|pdf], [|other] ] Confinement of Half-quantized Vortices in Coherently Coupled Bose-Einstein Condensates: Simulating Quark Confinement in QCD [|Minoru Eto], [|Muneto Nitta]   Comments: 9 pages, 9 figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; High Energy Physics - Theory (hep-th) We demonstrate that the confinement of half-quantized vortices (HQVs) in coherently coupled Bose-Einstein condensates (BECs) simulates certain aspects of the confinement in  SU ( 2 )   quantum chromodynamics (QCD) in 2+1 space-time dimensions. By identifying the circulation of superfluid velocity as the baryon number and the relative phase between two components as a dual gluon, we identify HQVs in a single component as electrically charged particles with a half baryon number. Further, we show that only singlet states of the relative phase of two components can stably exist as bound states of vortices, that is, a pair of vortices in each component (a baryon) and a pair of a vortex and an antivortex in the same component (a meson). We then study the dynamics of a baryon and meson; baryon is static at the equilibrium and rotates once it deviates from the equilibrium, while a meson moves with constant velocity. For both baryon and meson we verify a linear confinement and determine that they are broken, thus creating other baryons or mesons in the middle when two constituent vortices are separated by more than some critical distance, resembling QCD.

= = = Feb 13 = [|arXiv:1702.03120] [ [|pdf], [|ps] , [|other] ] Deterministic entanglement generation from driving through quantum phase transitions [|Xin-Yu Luo], [|Yi-Quan Zou] , [|Ling-Na Wu] , [|Qi Liu] , [|Ming-Fei Han] , [|Meng Khoon Tey] , [|Li You]   Comments: Supplementary materials can be found at [|this http URL]   Journal-ref: Science 355, 620-623 (2017)  Subjects: Quantum Gases (cond-mat.quant-gas)  Many-body entanglement is often created through system evolution, aided by non-linear interactions between the constituting particles. The very dynamics, however, can also lead to fluctuations and degradation of the entanglement if the interactions cannot be controlled. Here, we demonstrate near-deterministic generation of an entangled twin-Fock condensate of  ∼ 11000  atoms by driving a  87  Rb Bose-Einstein condensate undergoing spin mixing through two consecutive quantum phase transitions (QPTs). We directly observe number squeezing of  10.7 ± 0.6  dB and normalized collective spin length of  0.99 ± 0.01  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">. Together, these observations allow us to infer an entanglement-enhanced phase sensitivity of <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> ∼ 6 <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> dB beyond the standard quantum limit and an entanglement breadth of <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> ∼ 910  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> atoms. Our work highlights the power of generating large-scale useful entanglement by taking advantage of the different entanglement landscapes separated by QPTs.

[|arXiv:1702.02935] [ [|pdf], [|other] ] Quasiparticle energy in a strongly interacting homogeneous Bose-Einstein condensate [|Raphael Lopes], [|Christoph Eigen] , [|Adam Barker] , [|Konrad G. H. Viebahn] , [|Martin Robert-de-Saint-Vincent] , [|Nir Navon] , [|Zoran Hadzibabic] , [|Robert P. Smith]   Comments: 4 pages, 4 figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph) Using two-photon Bragg spectroscopy, we study the energy of particle-like excitations in a strongly interacting homogeneous Bose-Einstein condensate, and observe dramatic deviations from Bogoliubov theory. In particular, at large scattering length <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">a the shift of the excitation resonance from the free-particle energy changes sign from positive to negative. For an excitation with wavenumber <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">q, this sign change occurs at <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">a <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;">4 <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">/( <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">πq <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">)  , in agreement with the Feynman energy relation and the static structure factor expressed in terms of the two-body contact. For <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">a <span class="mo" style="font-family: MathJax_AMS; font-size: 17.28px; vertical-align: 0px;">≳ <span class="mn" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">3 <span class="mo" style="font-family: MathJax_Main; font-size: 17.28px; vertical-align: 0px;">/ <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">q we also see a breakdown of this theory, and better agreement with calculations based on the Wilson operator product expansion. Neither theory explains our observations across all interaction regimes, inviting further theoretical efforts.
 * Feb 10**

**Feb 7**
=<span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: x-large;">Chiral Spin Condensation in a One-Dimensional Optical Lattice = [|Ying-Hai Wu], [|Xiaopeng Li] , [|S. Das Sarma] (Submitted on 5 Feb 2017) > We study a spinor (two component) Bose gas confined in a one dimensional double-valley optical lattice which has a double-well structure in momentum space. Based on field theory analysis, it is found that the spinor bosons in the double-valley band generically form a spin-charge mixed chiral spin quasi-condensate. Our numerical calculations in a concrete <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">π -flux triangular ladder system confirm the robustness of the chiral spin order against interactions and quantum fluctuations. This exotic atomic Bose-Einstein condensate exhibits spatially staggered spin loop currents without any charge dynamics despite the complete absence of spin-orbit coupling in the system, paving a novel venue towards atom-spintronics. The entanglement entropy scaling allows us to extract conformal-field-theory central charge and establish the low energy effective field theory for the chiral spin condensate as a two-component Luttinger liquid. Our predictions should be detectable in atomic experiments through spin resolved time-of-flight techniques.

** Feb 1 **
[|arXiv:1702.00197] [ [|pdf], [|other] ] Majorana zero modes without edges [|Kohei Kawabata], [|Ryohei Kobayashi] , [|Ning Wu] , [|Hosho Katsura]   Comments: 14 pages, 6 figures  Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); Mathematical Physics (math-ph) We study the Kitaev chain under generalized twisted boundary conditions, for which both the amplitudes and the phases of the boundary couplings can be tuned at will. We explicitly show the presence of Majorana zero modes for large chains belonging to the topological phase in the most general case, in spite of the absence of "edges" in the system. For specific values of the phase parameters, we rigorously obtain the condition for the presence of the Majorana zero modes in finite chains, and show that the zero modes obtained are indeed localized. The full spectrum of the twisted chain with zero chemical potential is analytically presented. Finally, we demonstrate the persistence of zero modes (level crossing) even in the presence of disorder or repulsive interactions.

[|arXiv:1702.00058] (cross-list from hep-th) [ [|pdf], [|ps] , [|other] ] Quantum Information Metric and Berry Curvature from a Lagrangian Approach [|Javier Alvarez-Jimenez], [|Aldo Dector] , [|J. David Vergara]   Comments: 33 pages  Subjects: High Energy Physics - Theory (hep-th) ; Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph) We take as a starting point an expression for the quantum geometric tensor re- cently derived in the context of the gauge/gravity duality. We proceed to generalize this formalism in such way it is possible to compute the geometrical phases of quantum systems. Our scheme provides a conceptually complete description and introduce a dif- ferent point of view of earlier works. Using our formalism, we show how this expression can be applied to well-known quantum mechanical systems.

[|arXiv:1702.00173] (cross-list from quant-ph) [ [|pdf], [|other] ] Relation between <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 21.6px; vertical-align: 0px;">PT -symmetry breaking and topologically nontrivial phases in the SSH and Kitaev models  [|Marcel Klett], [|Holger Cartarius] , [|Dennis Dast] , [|Jörg Main] , [|Günter Wunner]   Comments: 7 pages, 5 figures  Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) Non-Hermitian systems with <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT symmetry can possess purely real eigenvalue spectra. In this work two one-dimensional systems with two different topological phases, the topological nontrivial Phase (TNP) and the topological trivial phase (TTP) combined with <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT -symmetric non-Hermitian potentials are investigated. The models of choice are the Su-Schrieffer-Heeger (SSH) model and the Kitaev chain. The interplay of a spontaneous <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT -symmetry breaking due to gain and loss with the topological phase is different for the two models. The SSH model undergoes a <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT -symmetry breaking transition in the TNP immediately with the presence of a non-vanishing gain and loss strength <span class="mi" style="font-family: MathJax_Math-italic; font-size: 17.28px; vertical-align: 0px;">γ , whereas the TTP exhibits a parameter regime in which a purely real eigenvalue spectrum exists. For the Kitaev chain the <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT -symmetry breaking is independent of the topological phase. We show that the topological interesting states -- the edge states -- are the reason for the different behaviors of the two models and that the intrinsic particle-hole symmetry of the edge states in the Kitaev chain is responsible for a conservation of <span class="mi" style="font-family: MathJax_Caligraphic; font-size: 17.28px; vertical-align: 0px;">PT symmetry in the TNP.