Double Semion Phase in an Exactly Solvable Quantum Dimer Model on the Kagome Lattice

Quantum dimer models typically arise in various low energy theories like those of frustrated antiferromagnets. We introduce a quantum dimer model on the kagome lattice which stabilizes an alternative $\mathbb{Z}_2$ topological order, namely the so-called "double semion" order. For a particular set of parameters, the model is exactly solvable, allowing us to access the ground state as well as the excited states. We show that the double semion phase is stable over a wide range of parameters using numerical exact diagonalization. Furthermore, we propose a simple microscopic spin Hamiltonian for which the low-energy physics is described by the derived quantum dimer model.Comment: 7 pages, 5 figure

Sub-ballistic growth of R\'enyi entropies due to diffusion

We investigate the dynamics of quantum entanglement after a global quench and uncover a qualitative difference between the behavior of the von Neumann entropy and higher R\'enyi entropies. We argue that the latter generically grow \emph{sub-ballistically}, as $\propto\sqrt{t}$, in systems with diffusive transport. We provide strong evidence for this in both a U$(1)$ symmetric random circuit model and in a paradigmatic non-integrable spin chain, where energy is the sole conserved quantity. We interpret our results as a consequence of local quantum fluctuations in conserved densities, whose behavior is controlled by diffusion, and use the random circuit model to derive an effective description. We also discuss the late-time behavior of the second R\'enyi entropy and show that it exhibits hydrodynamic tails with \emph{three distinct power laws} occurring for different classes of initial states.Comment: close to published version: 4 + epsilon pages, 3 figures + supplemen

Diffusive hydrodynamics of out-of-time-ordered correlators with charge conservation

The scrambling of quantum information in closed many-body systems, as measured by out-of-time-ordered correlation functions (OTOCs), has lately received considerable attention. Recently, a hydrodynamical description of OTOCs has emerged from considering random local circuits, aspects of which are conjectured to be universal to ergodic many-body systems, even without randomness. Here we extend this approach to systems with locally conserved quantities (e.g., energy). We do this by considering local random unitary circuits with a conserved U$(1)$ charge and argue, with numerical and analytical evidence, that the presence of a conservation law slows relaxation in both time ordered {\textit{and}} out-of-time-ordered correlation functions, both can have a diffusively relaxing component or "hydrodynamic tail" at late times. We verify the presence of such tails also in a deterministic, peridocially driven system. We show that for OTOCs, the combination of diffusive and ballistic components leads to a wave front with a specific, asymmetric shape, decaying as a power law behind the front. These results also explain existing numerical investigations in non-noisy ergodic systems with energy conservation. Moreover, we consider OTOCs in Gibbs states, parametrized by a chemical potential $\mu$, and apply perturbative arguments to show that for $\mu\gg 1$ the ballistic front of information-spreading can only develop at times exponentially large in $\mu$ -- with the information traveling diffusively at earlier times. We also develop a new formalism for describing OTOCs and operator spreading, which allows us to interpret the saturation of OTOCs as a form of thermalization on the Hilbert space of operators.Comment: Close to published version: 17 + 9.5 pages. Improved presentation. Contains new section on clean Floquet spin chain. New and/or improved numerical data in Figures 4-7, 11, 1

Correlated Fermions on a Checkerboard Lattice

A model of strongly correlated spinless fermions hopping on a checkerboard lattice is mapped onto a quantum fully-packed loop model. We identify a large number of fluctuationless states specific to the fermionic case. We also show that for a class of fluctuating states, the fermionic sign problem can be gauged away. This claim is supported by numerically evaluating the energies of the low-lying states. Furthermore, we analyze in detail the excitations at the Rokhsar-Kivelson point of this model thereby using the relation to the height model and the single-mode approximation.Comment: 4 Pages, 3 Figures; v4: updated version published in Phys. Rev. Lett.; one reference adde

Spectral functions for strongly correlated 5f-electrons

We calculate the spectral functions of model systems describing 5f-compounds adopting Cluster Perturbation Theory. The method allows for an accurate treatment of the short-range correlations. The calculated excitation spectra exhibit coherent 5f bands coexisting with features associated with local intra-atomic transitions. The findings provide a microscopic basis for partial localization. Results are presented for linear chains.Comment: 10 Page

The Misprediction of emotions in Track Athletics.: Is experience the teacher of all things?

People commonly overestimate the intensity of their emotions toward future events. In other words, they display an impact bias. This research addresses the question whether people learn from their experiences and correct for the impact bias. We hypothesize that athletes display an impact bias and, counterintuitively, that increased experience with an event increases this impact bias. A field study in the context of competitive track athletics supported our hypotheses by showing that athletes clearly overestimated their emotions toward the outcome of a track event and that this impact bias was more pronounced for negative events than for positive events. Moreover, with increased athletic experience this impact bias became larger. This effect could not be explained by athletes’ forecasted emotions, but it could be explained by the emotions they actually felt following the race. The more experience athletes had with athletics, the less they felt negative emotions after unsuccessful goal attainment. These findings are discussed in relation to possible underlying emotion regulation processes

Linear quantum quench in the Heisenberg XXZ chain: Time-dependent Luttinger-model description of a lattice system

We study variable-rate linear quenches in the anisotropic Heisenberg (XXZ) chain, starting at the XX point. This is equivalent to switching on a nearest-neighbor interaction for hard-core bosons or an interaction quench for free fermions. The physical observables we investigate are the energy pumped into the system during the quench, the spin-flip correlation function, and the bipartite fluctuations of the z component of the spin in a box. We find excellent agreement between exact numerics (infinite system time-evolving block decimation) and analytical results from bosonization, as a function of the quench time, spatial coordinate, and interaction strength. This provides a stringent and much-needed test of Luttinger liquid theory in a nonequilibrium situation. DOI: 10.1103/PhysRevB.87.04110