Systematic Construction of Scarred Many-Body Dynamics in 1D Lattice Models.

We introduce a family of nonintegrable 1D lattice models that feature robust periodic revivals under a global quench from certain initial product states, thus generalizing the phenomenon of many-body scarring recently observed in Rydberg atom quantum simulators. Our construction is based on a systematic embedding of the single-site unitary dynamics into a kinetically constrained many-body system. We numerically demonstrate that this construction yields new families of models with robust wave-function revivals, and it includes kinetically constrained quantum clock models as a special case. We show that scarring dynamics in these models can be decomposed into a period of nearly free clock precession and an interacting bottleneck, shedding light on their anomalously slow thermalization when quenched from special initial states.

Generalized Pseudopotentials for the Anisotropic Fractional Quantum Hall Effect.

We generalize the notion of Haldane pseudopotentials to anisotropic fractional quantum Hall (FQH) systems that are physically realized, e.g., in tilted magnetic field experiments or anisotropic band structures. This formalism allows us to expand any translation-invariant interaction over a complete basis, and directly reveals the intrinsic metric of incompressible FQH fluids. We show that purely anisotropic pseudopotentials give rise to new types of bound states for small particle clusters in the infinite plane, and can be used as a diagnostic of FQH nematic order. We also demonstrate that generalized pseudopotentials quantify the anisotropic contribution to the effective interaction potential, which can be particularly large in models of fractional Chern insulators.

Publisher's Note: Generalized Pseudopotentials for the Anisotropic Fractional Quantum Hall Effect [Phys. Rev. Lett. 118, 146403 (2017)].

This corrects the article DOI: 10.1103/PhysRevLett.118.146403.

Power-Law Entanglement Spectrum in Many-Body Localized Phases.

The entanglement spectrum of the reduced density matrix contains information beyond the von Neumann entropy and provides unique insights into exotic orders or critical behavior of quantum systems. Here, we show that strongly disordered systems in the many-body localized phase have power-law entanglement spectra, arising from the presence of extensively many local integrals of motion. The power-law entanglement spectrum distinguishes many-body localized systems from ergodic systems, as well as from ground states of gapped integrable models or free systems in the vicinity of scale-invariant critical points. We confirm our results using large-scale exact diagonalization. In addition, we develop a matrix-product state algorithm which allows us to access the eigenstates of large systems close to the localization transition, and discuss general implications of our results for variational studies of highly excited eigenstates in many-body localized systems.

Many-body localization in periodically driven systems.

We consider disordered many-body systems with periodic time-dependent Hamiltonians in one spatial dimension. By studying the properties of the Floquet eigenstates, we identify two distinct phases: (i) a many-body localized (MBL) phase, in which almost all eigenstates have area-law entanglement entropy, and the eigenstate thermalization hypothesis (ETH) is violated, and (ii) a delocalized phase, in which eigenstates have volume-law entanglement and obey the ETH. The MBL phase exhibits logarithmic in time growth of entanglement entropy when the system is initially prepared in a product state, which distinguishes it from the delocalized phase. We propose an effective model of the MBL phase in terms of an extensive number of emergent local integrals of motion, which naturally explains the spectral and dynamical properties of this phase. Numerical data, obtained by exact diagonalization and time-evolving block decimation methods, suggest a direct transition between the two phases.

Topological phases in the zeroth Landau level of bilayer graphene.

We analyze the phase diagram of the zeroth Landau level of bilayer graphene, taking into account the realistic effects of screening of the Coulomb interaction and strong mixing between two degenerate sublevels. We identify robust quantum Hall states at filling factors ν=-1, -4/3, -5/3, -8/5, -1/2 and discuss the nature of their ground states, collective excitations, and relation to the more familiar states in GaAs using a tractable model. In particular, we present evidence that the ν=-1/2 state is non-Abelian and described by either the Moore-Read wave function or its particle-hole conjugate, while ruling out other candidates such as the 331 state.

Interferometric probes of many-body localization.

We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a noninteracting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold-atom systems.

Local conservation laws and the structure of the many-body localized states.

We construct a complete set of local integrals of motion that characterize the many-body localized (MBL) phase. Our approach relies on the assumption that local perturbations act locally on the eigenstates in the MBL phase, which is supported by numerical simulations of the random-field XXZ spin chain. We describe the structure of the eigenstates in the MBL phase and discuss the implications of local conservation laws for its nonequilibrium quantum dynamics. We argue that the many-body localization can be used to protect coherence in the system by suppressing relaxation between eigenstates with different local integrals of motion.

Universal slow growth of entanglement in interacting strongly disordered systems.

Recent numerical work by Bardarson, Pollmann, and Moore revealed a slow, logarithmic in time, growth of the entanglement entropy for initial product states in a putative many-body localized phase. We show that this surprising phenomenon results from the dephasing due to exponentially small interaction-induced corrections to the eigenenergies of different states. For weak interactions, we find that the entanglement entropy grows as ξln(Vt/ℏ), where V is the interaction strength, and ξ is the single-particle localization length. The saturated value of the entanglement entropy at long times is determined by the participation ratios of the initial state over the eigenstates of the subsystem. Our work shows that the logarithmic entanglement growth is a universal phenomenon characteristic of the many-body localized phase in any number of spatial dimensions, and reveals a broad hierarchy of dephasing time scales present in such a phase.

Quantum phase transitions and the ν=5/2 fractional Hall state in wide quantum wells.

We study the nature of the ν=5/2 quantum Hall state in wide quantum wells under the mixing of electronic subbands and Landau levels. A general method is introduced to analyze the Moore-Read pfaffian state and its particle-hole conjugate, the anti-pfaffian state, under periodic boundary conditions in a "quartered" Brillouin zone scheme containing both even and odd numbers of electrons. By examining the rotational quantum numbers on the torus, we show spontaneous breaking of the particle-hole symmetry can be observed in finite-size systems. In the presence of electronic-subband and Landau-level mixing, the particle-hole symmetry is broken in such a way that the anti-pfaffian state is unambiguously favored, and becomes more robust in the vicinity of a transition to the compressible phase, in agreement with recent experiments.

Model wave functions for the collective modes and the magnetoroton theory of the fractional quantum Hall effect.

We construct model wave functions for the collective modes of fractional quantum Hall systems. The wave functions are expressed in terms of symmetric polynomials characterized by a root partition that defines a "squeezed" basis, and show excellent agreement with exact diagonalization results for finite systems. In the long wavelength limit, we prove that the model wave functions are identical to those predicted by the single-mode approximation, leading to intriguing interpretations of the collective modes from the perspective of the ground-state guiding-center metric.

Tunable electron interactions and fractional quantum Hall States in graphene.

The recent discovery of fractional quantum Hall (FQH) states in graphene raises the question of whether the physics of graphene offers any advantages over GaAs-based materials in exploring strongly correlated states of two-dimensional electrons. Here we propose a method to continuously tune the effective electron interactions in graphene and its bilayer by the dielectric environment of the sample. Using this method, the charge gaps of prominent FQH states, including ν=1/3 or ν=5/2 states, can be increased several times, or reduced to zero. The tunability of the interactions can be used to realize and stabilize various strongly correlated phases and explore the transitions between them.

Topological entanglement in Abelian and non-Abelian excitation eigenstates.

Entanglement in topological phases of matter has so far been investigated through the perspective of their ground-state wave functions. In contrast, we demonstrate that the excitations of fractional quantum Hall (FQH) systems also contain information to identify the system's topological order. Entanglement spectrum of the FQH quasihole (QH) excitations is shown to differentiate between the conformal field theory (CFT) sectors, based on the relative position of the QH with respect to the entanglement cut. For Read-Rezayi model states, as well as Coulomb interaction eigenstates, the counting of the QH entanglement levels in the thermodynamic limit matches exactly the CFT counting, and sector changes occur as non-Abelian quasiholes successively cross the entanglement cut.

Atypical fractional quantum Hall effect in graphene at filling factor 1/3.

We study, with the help of exact-diagonalization calculations, a four-component trial wave function that may be relevant for the recently observed graphene fractional quantum Hall state at a filling factor ν(G) = 1/3. Although it is adiabatically connected to a 1/3 Laughlin state in the upper spin branch, with SU(2) valley-isospin ferromagnetic ordering and a completely filled lower spin branch, it reveals physical properties beyond such a state that is the natural ground state for a large Zeeman effect. Most saliently, it possesses at experimentally relevant values of the Zeeman gap low-energy spin-flip excitations that may be unveiled in inelastic light-scattering experiments.

Treatment of respiratory syncytial virus infection with vitamin A: a randomized, placebo-controlled trial in Santiago, Chile.

BACKGROUND: Treatment with high dose vitamin A reduces complications and duration of hospitalization for children with measles. In respiratory syncytial virus (RSV) infection, as with measles, low serum vitamin A concentrations correlate with increased severity of illness. METHODS: To determine whether high dose vitamin A treatment is also effective for treating RSV disease, we conducted a randomized, double blind, placebo-controlled trial among 180 RSV-infected children between 1 month and 6 years of age at three hospitals in Santiago, Chile. Children with nasal washes positive for RSV antigen were given oral vitamin A (50,000 to 200,000 IU of retinyl palmitate, doses according to age; n = 89) or placebo (n = 91) within 2 days of admission. RESULTS: There was no significant benefit from vitamin A treatment for the overall group in duration of hospitalization, need for supplemental oxygen or time to resolve hypoxemia. For the subgroup of children with significant hypoxemia on admission (room air oxygen saturation level < or = 90%), those given vitamin A had more rapid resolution of tachypnea (P = 0.01) and a shorter duration of hospitalization (5.5 vs. 9.3 days, P = 0.09). No toxicities were seen, including excess vomiting or bulging fontanel. CONCLUSIONS: If vitamin A has a beneficial effect on the course of RSV disease, it may be seen only in more severely ill children.

The cytologic identification and quantification of testicular cell subtypes. Reproducibility and relation to histologic findings in the diagnosis of male infertility.

In testicular imprint smears from 100 infertile men (both testicles), stained using the Pappenheim and Papanicolaou methods, the cell forms (light and dark spermatogonia, primary and secondary spermatocytes, spermatids, spermatozoa and Sertoli cells) were identified and quantified by the counting of 500 consecutive cells. Identification of the cell types, which are described and illustrated, was consistent and reproducible; the advantages of the different stainings in their analysis is documented. The cell counts were tested for reproducibility and compared to the histologic diagnoses and sperm counts. Statistical analysis showed the highest reproducibility for cells frequently encountered in smears (0.99 for Sertoli cells and 0.98 for spermatozoa) and the lowest but still satisfactory reproducibility for rare or arbitrarily defined cell forms (0.71 for dark spermatogonia and 0.76 for secondary spermatocytes). The high reproducibility of the smear quantification permits the introduction of a number of indices, defining clinically useful relations between cell types that are indicative of various types of infertility. The data obtained by cytologic quantification showed reasonably good correlation with the histologic diagnoses of desquamation and focal fibrosis and excellent correlation with Sertoli cells only, arrested spermatogenesis and complete fibrosis. The cytologic quantification of testicular smears adds considerable information to the diagnosis of impaired fertility and should be instituted in properly equipped centers.

[Cytochemical study of the thyroid gland]. / Citohemijska ispitivanja stitaste zlezde.

The paper presents the importance of cytochemical research in the diagnostics of thyroid gland diseases. It is considered that this research usefully supplements the standard cytodiagnostics of the thyroid, especially in clarifying functional and morphological changes in goiter. Given are the basic principals of cytochemical analyses as well as the valuing, in other words, the quantification of cytochemical results. The following methods are more closely described: PAS, alpha-naphthilacetate esterase, naphthol AS-D acetate esterase, peroxidase, beta-glucuronidase and alkaline phosphatase.

[Biopsy of the external ear in diabetology]. / Biopsija usne skoljke u dijabetologiji.

In the introductory part the authors pointed to the need for the application of the morphologic method which would make possible the estimation of the existence and degree of miocroangiopathic changes. Microangiopathic changes were observed on the material obtained by skin biopsy of the auricle and the reason for selecting this localization was explained. It was performed in the representative sample consisting of 441 patients with diabetes mellitus and 92 persons with disturbed glucose tolerance and the objective indicators for small blood vessel changes were confirmed by the analysis of the material obtained by the method described. The possibility of the quantification of the degree of these changes was at the same time presented and illustrated. Finally, the authors came to the conclusion that reproducibility of these quantifications was satisfactory. Thereby, they were of the opinion that in their further work they could compare described and quantificated changes in respect to individual vital characteristics of the investigated group, the existence of factors considered risky for the appearance of diabetes mellitus complications and the degree of their development.

Comparison between cytochemical changes, concentration of PAS-positive substances in peripheral blood lymphocytes and changes of blood glucose values during the oral glucose tolerance test.

The purpose of the study was to analyse the correlation between the blood glucose values and the quantity of PAS-positive substances in lymphocytes observed in different groups of subjects during oral glucose loading. In 300 subjects--100 persons with a normal OGTT, 100 pregnant women (with normal, borderline and diabetic OGTT), 50 diabetic patients, 20 borderline cases of diabetes, and 30 persons with a 'lag form' OGIT--the PAS-index was measured at each point of the OGTT. The values of the PAS-index curve followed the values of the blood glucose level, and the results obtained in different groups of persons were compared. It has been shown that an increased value of the PAS-index is an early sign of disturbed carbohydrate metabolism and that differences between borderline and manifest diabetics, as well as between these groups and normal control persons, are significant.