Difference between revisions of "Jul 2018"

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(Created page with "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...")
 
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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
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Jul 1 - Jul 2 Biao Huang, Jul 3- Jul 7 Xuguang Yue, Jul 8- Jul 12 Haiyuan Zou, Jul 13- Jul 17 Zehan Li, Jul 18- Jul 22 Jiansong Pan, Jul 23-Jul 27 Ahmet Keles, Jul 28- Jul 31 Max Aarzamazovs
  
  
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  <nowiki>Jun 7
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  <nowiki>Jul 12
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arXiv:1806.01852 [pdf, other]
 
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Bilayer Kitaev models: Phase diagrams and novel phases
 
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Urban F. P. Seifert, Julian Gritsch, Erik Wagner, Darshan G. Joshi, Wolfram Brenig, Matthias Vojta, Kai P. Schmidt
 
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Comments: 22 pages, 18 figures
 
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Subjects: Strongly Correlated Electrons (cond-mat.str-el)
 
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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.
 
  
  
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arXiv:1807.03838 [pdf, ps, other]
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Static properties of two connected Bose-Hubbard rings
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Albert Escrivà, Bruno Juliá-Díaz, Montserrat Guilleumas
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Subjects: Quantum Gases (cond-mat.quant-gas)
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We consider two coupled Bose-Hubbard rings populated with ultra-cold bosons with repulsive interactions. The atoms can either tunnel between the sites of the same ring, with a given inter-ring coupling, or between the sites of different rings coupled by an intra-ring coupling. By solving the corresponding Bose-Hubbard Hamiltonian we obtain the many-body ground state for different values of the interaction and tunneling strengths. We characterize the static many-body properties of the ground state by means of coherence, correlations and entanglement.
  
  
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Jun 6
 
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arXiv:1806.01582 [pdf, ps, other]
 
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Fulde-Ferrell-Larkin-Ovchinnikov pairing states of a polarized dipolar Fermi gas trapped in a one-dimensional optical lattice
 
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Xingbo Wei, Chao Gao, Reza Asgari, Pei Wang, Gao Xianlong
 
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Comments: 8 pages, 11 figures, typos corrected
 
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Subjects: Quantum Gases (cond-mat.quant-gas)
 
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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.
 
  
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Jul 11
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arXiv:1807.03572 [pdf, other]
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Heat distribution of a quantum harmonic oscillator
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Tobias Denzler, Eric Lutz
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Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
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We consider a thermal quantum harmonic oscillator weakly coupled to a heat bath at a different temperature. We analytically study the quantum heat exchange statistics between the two systems using the quantum-optical master equation. We exactly compute the characteristic function of the heat distribution and show that it verifies the Jarzynski-W\'ojcik fluctuation theorem. We further evaluate the heat probability density in the limit of long thermalization times, both in the low and high temperature regimes, and investigate its time evolution by calculating its first two cumulants.
  
  
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Jul 10
  
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Jun 5
 
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arXiv:1806.00624 [pdf, other]
 
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Rényi entropies of generic thermodynamic macrostates in integrable systems
 
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Marton Mestyán, Vincenzo Alba, Pasquale Calabrese
 
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Comments: 22 pages, 6 figures
 
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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)
 
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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.
 
  
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arXiv:1807.02577 [pdf, other]
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Light-induced coherence in an atom-cavity system
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Christoph Georges, Jayson G. Cosme, Ludwig Mathey, Andreas Hemmerich
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Comments: 5 page, 3 figures
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Subjects: Quantum Gases (cond-mat.quant-gas)
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We demonstrate light-induced formation of coherence in a cold atomic gas system that utilizes the suppression of a competing density wave (DW) order. The condensed atoms are placed in an optical cavity and pumped by an external optical standing wave, which induces a long-range interaction, mediated by photon scattering, and DW order above a critical pump strength. We show that light induced modulation of the pump wave can suppress this DW order and restore coherence. This establishes a foundational principle of dynamical control of competing orders analogous to a hypothesized mechanism for light induced superconductivity in high-$T_c$ cuprates.
  
  
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Jun 4
 
  
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arXiv:1806.00022 [pdf, other]
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Jul 9
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Scrambling and entanglement spreading in long-range spin chains
 
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Silvia Pappalardi, Angelo Russomanno, Bojan Žunkovič, Fernando Iemini, Alessandro Silva, Rosario Fazio
 
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Comments: 6 pages, 4 figures and Supplementary Material
 
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Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
 
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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.
 
  
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arXiv:1806.00472 [pdf, other]
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arXiv:1807.02146 [pdf, other]
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Quantum Information Scrambling Through a High-Complexity Operator Mapping
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Absence of Criticality in the Phase Transitions of Open Floquet Systems
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Xiaopeng Li, Guanyu Zhu, Muxin Han, Xin Wang
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Steven Mathey, Sebastian Diehl
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Comments: 9 pages, 5 figures
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Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
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Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Computational Complexity (cs.CC); High Energy Physics - Theory (hep-th)
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Floquet systems hold the promise to realize novel phases of matter without equilibrium counterpart. The coupling to a bath can stabilize a stationary state at finite energy density. We address here the nature of phase transitions in such systems at rapid drive, complementary to the Kibble-Zurek scenario at slow drive. While the infinitely rapidly driven limit exhibits a second order phase transition, here we reveal a universal mechanism showing that fluctuations associated to the first rotating wave correction drive the transition first order at any finite driving. The effect is rooted in the degeneracy of critical poles in weakly coupled higher Floquet-Brillouin zones, in some analogy to the Coleman-Weinberg or Halperin-Lubensky-Ma phenomenon. The critical exponents of the infinitely rapidly driven fixed point -- including a new, independent one -- can be probed experimentally upon smoothly tuning towards that limit.</nowiki>
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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.</nowiki>
 

Revision as of 16:35, 9 October 2018

Jul 1 - Jul 2 Biao Huang, Jul 3- Jul 7 Xuguang Yue, Jul 8- Jul 12 Haiyuan Zou, Jul 13- Jul 17 Zehan Li, Jul 18- Jul 22 Jiansong Pan, Jul 23-Jul 27 Ahmet Keles, Jul 28- Jul 31 Max Aarzamazovs 


Jul 12


arXiv:1807.03838 [pdf, ps, other]
Static properties of two connected Bose-Hubbard rings
Albert Escrivà, Bruno Juliá-Díaz, Montserrat Guilleumas
Subjects: Quantum Gases (cond-mat.quant-gas)
We consider two coupled Bose-Hubbard rings populated with ultra-cold bosons with repulsive interactions. The atoms can either tunnel between the sites of the same ring, with a given inter-ring coupling, or between the sites of different rings coupled by an intra-ring coupling. By solving the corresponding Bose-Hubbard Hamiltonian we obtain the many-body ground state for different values of the interaction and tunneling strengths. We characterize the static many-body properties of the ground state by means of coherence, correlations and entanglement.



Jul 11

arXiv:1807.03572 [pdf, other]
Heat distribution of a quantum harmonic oscillator
Tobias Denzler, Eric Lutz
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
We consider a thermal quantum harmonic oscillator weakly coupled to a heat bath at a different temperature. We analytically study the quantum heat exchange statistics between the two systems using the quantum-optical master equation. We exactly compute the characteristic function of the heat distribution and show that it verifies the Jarzynski-W\'ojcik fluctuation theorem. We further evaluate the heat probability density in the limit of long thermalization times, both in the low and high temperature regimes, and investigate its time evolution by calculating its first two cumulants.


Jul 10


arXiv:1807.02577 [pdf, other]
Light-induced coherence in an atom-cavity system
Christoph Georges, Jayson G. Cosme, Ludwig Mathey, Andreas Hemmerich
Comments: 5 page, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We demonstrate light-induced formation of coherence in a cold atomic gas system that utilizes the suppression of a competing density wave (DW) order. The condensed atoms are placed in an optical cavity and pumped by an external optical standing wave, which induces a long-range interaction, mediated by photon scattering, and DW order above a critical pump strength. We show that light induced modulation of the pump wave can suppress this DW order and restore coherence. This establishes a foundational principle of dynamical control of competing orders analogous to a hypothesized mechanism for light induced superconductivity in high-$T_c$ cuprates.



Jul 9

arXiv:1807.02146 [pdf, other]
Absence of Criticality in the Phase Transitions of Open Floquet Systems
Steven Mathey, Sebastian Diehl
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
Floquet systems hold the promise to realize novel phases of matter without equilibrium counterpart. The coupling to a bath can stabilize a stationary state at finite energy density. We address here the nature of phase transitions in such systems at rapid drive, complementary to the Kibble-Zurek scenario at slow drive. While the infinitely rapidly driven limit exhibits a second order phase transition, here we reveal a universal mechanism showing that fluctuations associated to the first rotating wave correction drive the transition first order at any finite driving. The effect is rooted in the degeneracy of critical poles in weakly coupled higher Floquet-Brillouin zones, in some analogy to the Coleman-Weinberg or Halperin-Lubensky-Ma phenomenon. The critical exponents of the infinitely rapidly driven fixed point -- including a new, independent one -- can be probed experimentally upon smoothly tuning towards that limit.
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