Jun 2018

Jun 1- Jun 2 Xuguang Yue, Jun 3- Jun 7 Haiyuan Zou, Jun 8- Jun 12 Zehan Li, Jun 13- Jun 17 Jiansong Pan, Jun 18-Jun 22 Ahmet Keles, Jun 23- Jun 27 Max Aarzamazovs, Jun 28- Jun 30 Biao Huang

Jun 7
arXiv:1806.01852 [pdf, other]
Bilayer Kitaev models: Phase diagrams and novel phases
Urban F. P. Seifert, Julian Gritsch, Erik Wagner, Darshan G. Joshi, Wolfram Brenig, Matthias Vojta, Kai P. Schmidt
Comments: 22 pages, 18 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Kitaev's honeycomb-lattice spin-$1/2$ model has become a paradigmatic example for $\mathbb{Z}_2$ quantum spin liquids, both gapped and gapless. Here we study the fate of these spin-liquid phases in differently stacked bilayer versions of the Kitaev model. Increasing the ratio between the inter-layer Heisenberg coupling $J_\perp$ and the intra-layer Kitaev couplings $K^{x,y,z}$ destroys the topological spin liquid in favor of a paramagnetic dimer phase. We study phase diagrams as a function of $J_\perp/K$ and Kitaev coupling anisotropies using Majorana-fermion mean-field theory, and we employ different expansion techniques in the limits of small and large $J_\perp/K$. For strongly anisotropic Kitaev couplings, we derive effective models for the different layer stackings which we use to discuss the quantum phase transition out of the Kitaev phase. We find that the phase diagrams depend sensitively on the nature of the stacking and anisotropy strength. While in some stackings and at strong anisotropies we find a single transition between the Kitaev and dimer phases, other stackings are more involved: Most importantly, we prove the existence of two novel macro-spin phases which can be understood in terms of Ising chains which can be either coupled ferromagnetically, or remain degenerate, thus realizing a classical spin liquid. In addition, our results suggest the existence of a flux phase with spontaneous inter-layer coherence.




Jun 6
arXiv:1806.01582 [pdf, ps, other]
Fulde-Ferrell-Larkin-Ovchinnikov pairing states of a polarized dipolar Fermi gas trapped in a one-dimensional optical lattice
Xingbo Wei, Chao Gao, Reza Asgari, Pei Wang, Gao Xianlong
Comments: 8 pages, 11 figures, typos corrected
Subjects: Quantum Gases (cond-mat.quant-gas)
We study the interplay between the long- and short-range interaction of a one-dimensional optical lattice system of two-component dipolar fermions by using the density matrix renormalization group method. The atomic density profile, pairing-pairing correlation function, and the compressibility are calculated in the ground state, from which we identify the parameter region of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state, half-metal (HM) state, FFLO-HM state, and the normal polarized state, and thus the phase diagram in the coordinates of the long- and short-range interaction strength. The effect of the long-range dipolar interaction on the FFLO state is discussed in details. We find that the long-range part of the dipole-dipole interaction does not sweep away the FFLO superconducting region that is driven by the short-range interaction in the Hubbard model, and thus the FFLO state survives in the wide parameter space of the long-range interaction, polarization and the filling.




Jun 5
arXiv:1806.00624 [pdf, other]
Rényi entropies of generic thermodynamic macrostates in integrable systems
Marton Mestyán, Vincenzo Alba, Pasquale Calabrese
Comments: 22 pages, 6 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We study the behaviour of R\'enyi entropies in a generic thermodynamic macrostate of an integrable model. In the standard quench action approach to quench dynamics, the R\'enyi entropies may be derived from the overlaps of the initial state with Bethe eigenstates. These overlaps fix the driving term in the thermodynamic Bethe ansatz (TBA) formalism. We show that this driving term can be also reconstructed starting from the macrostate's particle densities. We then compute explicitly the stationary R\'enyi entropies after the quench from the dimer and the tilted N\'eel state in XXZ spin chains. For the former state we employ the overlap TBA approach, while for the latter we reconstruct the driving terms from the macrostate. We discuss in full details the limits that can be analytically handled and we use numerical simulations to check our results against the large time limit of the entanglement entropies.



Jun 4

arXiv:1806.00022 [pdf, other]
Scrambling and entanglement spreading in long-range spin chains
Silvia Pappalardi, Angelo Russomanno, Bojan Žunkovič, Fernando Iemini, Alessandro Silva, Rosario Fazio
Comments: 6 pages, 4 figures and Supplementary Material
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We study scrambling in connection to multipartite entanglement dynamics in regular and chaotic long-range spin chains, characterized by a well defined semi-classical limit. For regular dynamics, scrambling and entanglement dynamics are found to be very different: up to the Ehrenfest time they rise side by side departing only afterwards. Entanglement saturates and becomes extensively multipartite, while scrambling continues its growth up to the recurrence time. Remarkably, the exponential behaviour of scrambling emerges not only in the chaotic case, but also in the regular one, when the dynamics occurs at a dynamical critical point.

arXiv:1806.00472 [pdf, other]
Quantum Information Scrambling Through a High-Complexity Operator Mapping
Xiaopeng Li, Guanyu Zhu, Muxin Han, Xin Wang
Comments: 9 pages, 5 figures
Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Complexity (cs.CC); High Energy Physics - Theory (hep-th)
Recently, quantum information scrambling has attracted much attention amid the effort to reconcile the apparent conflict between quantum-mechanical unitarity and the irreversibility of thermalizaiton in quantum many-body systems. Here we propose an unconventional mechanism to generate quantum information scrambling through a high-complexity mapping from logical to physical degrees of freedom that hides the logical information into non-separable many-body correlations. We develop an algorithm to compute all physical observables in dynamics with a polynomial-in-system-size cost. The system shows information scrambling in the quantum many-body Hilbert space characterized by the spreading of Hamming distance defined by a set of a natural orbital bases, which can also be calculated with a time polynomial in system size. Despite the polynomial complexity, the operator-mapping enabled growth in the out-of-time-order-correlator still exhibits quantum chaotic behavior. The information-hiding mapping approach opens up a novel venue to investigate fundamental connections among computational complexity, information scrambling and quantum thermalization.