Publisher: John Wiley and Sons (Total: 1584 journals) A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1 2 3 4 5 6 7 8 | Last [Sort by number of followers] [Restore default list]
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Annalen der Physik [SJR: 1.46] [H-I: 40] [5 followers] Follow Hybrid journal (It can contain Open Access articles) ISSN (Print) 0003-3804 - ISSN (Online) 1521-3889 Published by John Wiley and Sons [1584 journals] |
- The Effect of the Multi-Environment for Quantum Correlation: Geometry
Discord vs Quantum Discord- Authors: Chang-Chun Ding; Qin-Sheng Zhu, Shao-Yi Wu, Wei Lai
Abstract: A two qubits system interacting with two independent spin-environments connecting with the third environment is constructed in order to demonstrate the effect of the multi-environment for quantum correlation. In this process, the freezing phenomenon appears for SCI and X states under Quantum Discord and Geometric Discord measures, respectively, but not for the same initial state measured by different measures. Meanwhile, the properties of the freezing platform, characterized by the collapse, revival and persistent time, are researched by the different parameters. The result of this paper may pave a way to control quantum correlation and design nanospintronic devices.The interacting muti-environment affects the properties of quantum correlation, even some environments do not directly interact with the system. The freezing behavior emerges only by the QD or GD method under the same condition and can be effectively affected by the intrinsic parameters (the coupling parameter b between the spin particles and environments, the environments temperature T and the coupling parameters q between the environments).
PubDate: 2017-07-20T08:37:08.874168-05:
DOI: 10.1002/andp.201700014
- Authors: Chang-Chun Ding; Qin-Sheng Zhu, Shao-Yi Wu, Wei Lai
- All-Optical Photonic Band Control in a Quantum Metamaterial
- Authors: D. Felbacq; E. Rousseau
Abstract: Metamaterials made of periodic collections of dielectric nanorods are considered theoretically. When quantum resonators are embedded within the nanorods, one obtains a quantum metamaterial, whose electromagnetic properties depend upon the state of the quantum resonators. The theoretical model predicts that when the resonators are pumped and reach the inversion regime, the quantum metamaterial exhibits an all-optical switchable conduction band. The phenomenon can be described by considering the pole stucture of the scattering matrix of the metamaterial.Quantum metamaterials are metamaterials in which quantum degrees of freedom are inserted. Such a metamaterial comprising quantum dots is presented. It is predicted that there exists a photonic conduction band that can be switched on and off by using an external pump field that serve to saturate the quantum dots and reach the emission regime.
PubDate: 2017-07-17T03:42:16.574003-05:
DOI: 10.1002/andp.201600371
- Authors: D. Felbacq; E. Rousseau
- Optimizing Weak Measurements to Detect Angular Deviations
- Authors: Manoel P. Araújo; Stefano Leo, Gabriel G. Maia
Abstract: We analyze and compare the angular deviations for an optical beam reflected by and transmitted through a dielectric triangular prism. The analytic expressions derived for the angular deviations hold for arbitrary incidence angles. For incidence approaching the internal and external Brewster angles, the angular deviations transverse magnetic waves present the same behavior leading to the well-known giant Goos-Hänchen angular shift. For incidence near the critical angle a new region of large shift is seen both for transverse magnetic and transverse electric waves. While a direct measuring procedure is better in the vicinity of the Brewster region, a weak measurement breaks off the giant Goos-Hänchen effect, preserving the amplification in the critical region. We discuss under which conditions it is possible to optimize the amplification and we also determine when a weak measurement is preferred to a direct measuring procedure.Angular deviations of a beam transmitted through a triangular dielectric block have been theoretically studied and related analytical expressions have been found. Using these analytical expresssions, the weak measurement procedure has been optimized showing a breaking off in the Brewester region and an effective amplification for incidence near the critical angle.
PubDate: 2017-07-17T03:41:58.035014-05:
DOI: 10.1002/andp.201600357
- Authors: Manoel P. Araújo; Stefano Leo, Gabriel G. Maia
- Ultra-Fast Control of Magnetic Relaxation in a Periodically Driven Hubbard
Model- Authors: Juan Jose Mendoza-Arenas; Fernando Javier Gómez-Ruiz, Martin Eckstein, Dieter Jaksch, Stephen R. Clark
Abstract: Motivated by cold atom and ultra-fast pump-probe experiments we study the melting of long-range antiferromagnetic order of a perfect Néel state in a periodically driven repulsive Hubbard model. The dynamics is calculated for a Bethe lattice in infinite dimensions with non-equilibrium dynamical mean-field theory. In the absence of driving melting proceeds differently depending on the quench of the interactions to hopping ratio U/ν0 from the atomic limit. For U≫ν0 decay occurs due to mobile charge-excitations transferring energy to the spin sector, while for ν0≳U it is governed by the dynamics of residual quasi-particles. Here we explore the rich effects that strong periodic driving has on this relaxation process spanning three frequency ω regimes: (i) high-frequency ω≫U,ν0, (ii) resonant lω=U>ν0 with integer l, and (iii) in-gap U>ω>ν0 away from resonance. In case (i) we can quickly switch the decay from quasi-particle to charge-excitation mechanism through the suppression of ν0. For (ii) the interaction can be engineered, even allowing an effective U=0 regime to be reached, giving the reverse switch from a charge-excitation to quasi-particle decay mechanism. For (iii) the exchange interaction can be controlled with little effect on the decay. By combining these regimes we show how periodic driving could be a potential pathway for controlling magnetism in antiferromagnetic materials. Finally, our numerical results demonstrate the accuracy and applicability of matrix product state techniques to the Hamiltonian DMFT impurity problem subjected to strong periodic driving.Motivated by state-of-the-art experiments on ultra-fast control of many-body quantum systems, the dynamics of a periodically-driven Hubbard lattice is analyzed in an infinite-dimensional Bethe geometry. Its evolution from an antiferromagetic state is simulated by combining nonequilibrium DMFT with a MPS impurity solver. Tuning the driving frequency, magnetic melting slowdown (high frequency), enhancement and dynamics reversal (resonance) are induced. Periodic driving thus provides a pathway for manipulating magnetism in complex systems.
PubDate: 2017-07-17T03:41:12.688786-05:
DOI: 10.1002/andp.201700024
- Authors: Juan Jose Mendoza-Arenas; Fernando Javier Gómez-Ruiz, Martin Eckstein, Dieter Jaksch, Stephen R. Clark
- Graphene Quantum Dots Probed by Scanning Tunneling Microscopy
- Authors: Markus Morgenstern; Nils Freitag, Alexander Nent, Peter Nemes-Incze, Marcus Liebmann
Abstract: Scanning tunneling spectroscopy results probing the electronic properties of graphene quantum dots are reviewed. After a short summary of the study of squared wave functions of graphene quantum dots on metal substrates, we firstly present data where the Landau level gaps caused by a perpendicular magnetic field are used to electrostatically confine electrons in monolayer graphene, which are probed by the Coulomb staircase revealing the consecutive charging of a quantum dot. It turns out that these quantum dots exhibit much more regular charging sequences than lithographically confined ones. Namely, the consistent grouping of charging peaks into quadruplets, both, in the electron and hole branch, portrays a regular orbital splitting of about 10meV. At low hole occupation numbers, the charging peaks are, partly, additionally grouped into doublets. The spatially varying energy separation of the doublets indicates a modulation of the valley splitting by the underlying BN substrate. We outline that this property might be used to eventually tune the valley splitting coherently. Afterwards, we describe graphene quantum dots with multiple contacts produced without lithographic resist, namely by local anodic oxidation. Such quantum dots target the goal to probe magnetotransport properties during the imaging of the corresponding wave functions by scanning tunneling spectroscopy.Graphene quantum dots are promising as qubits, but currently still suffer from too much disorder. Using scanning tunneling spectroscopy in ultrahigh vacuum, the authors aim to overcome these problems, e.g., by electrostatically inducing quantum dots into monolayer graphene exploiting the gaps caused by Landau quantization. An extraordinary quality of charging patterns results including reliable orbital and valley splittings. The authors review these and other efforts to optimize graphene quantum dots within an ultraclean environment.
PubDate: 2017-07-17T03:40:47.061385-05:
DOI: 10.1002/andp.201700018
- Authors: Markus Morgenstern; Nils Freitag, Alexander Nent, Peter Nemes-Incze, Marcus Liebmann
- Growth and Intercalation of Graphene on Silicon Carbide Studied by
Low-Energy Electron Microscopy- Authors: Florian Speck; Markus Ostler, Sven Besendörfer, Julia Krone, Martina Wanke, Thomas Seyller
Abstract: Based on its electronic, structural, chemical, and mechanical properties, many potential applications have been proposed for graphene. In order to realize these visions, graphene has to be synthesized, grown, or exfoliated with properties that are determined by the targeted application. Growth of so-called epitaxial graphene on silicon carbide by sublimation of silicon in an argon atmosphere is one particular method that could potentially lead to electronic applications. In this contribution we summarize our recent work on different aspects of epitaxial graphene growth and interface manipulation by intercalation, which was performed by a combination of low-energy electron microscopy, low-energy electron diffraction, atomic force microscopy and photoelectron spectroscopy.The sublimation growth of epitaxial graphene on silicon carbide in an argon atmosphere is one particular synthesis method that could potentially lead to electronic applications. The paper summarizes recent work on different aspects of epitaxial graphene growth and interface manipulation by intercalation, which was performed by a combination of low-energy electron microscopy, low-energy electron diffraction, atomic force microscopy and photoelectron spectroscopy.
PubDate: 2017-07-17T03:36:48.505472-05:
DOI: 10.1002/andp.201700046
- Authors: Florian Speck; Markus Ostler, Sven Besendörfer, Julia Krone, Martina Wanke, Thomas Seyller
- Carrier Dynamics in Graphene: Ultrafast Many-Particle Phenomena
- Authors: E. Malic; T. Winzer, F. Wendler, S. Brem, R. Jago, A. Knorr, M. Mittendorff, J. C. König-Otto, T. Plötzing, D. Neumaier, H. Schneider, M. Helm, S. Winnerl
Abstract: Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion.The feature article presents a review of recent theoretical work providing microscopic view on the time- and energy-resolved dynamics of optically excited carriers in graphene. The remarkable gapless and linear band structure of graphene opens up new relaxation channels giving rise to fascinating ultrafast phenomena. In this work, the authors focus on the appearance of technologially relevant carrier multiplication and population inversion.
PubDate: 2017-07-17T03:36:01.052022-05:
DOI: 10.1002/andp.201700038
- Authors: E. Malic; T. Winzer, F. Wendler, S. Brem, R. Jago, A. Knorr, M. Mittendorff, J. C. König-Otto, T. Plötzing, D. Neumaier, H. Schneider, M. Helm, S. Winnerl
- Spectral Classification of One-Dimensional Binary Aperiodic Crystals: An
Algebraic Approach- Authors: Enrique Maciá
Abstract: A spectral classification of general one-dimensional binary aperiodic crystals (BACs) based on both their diffraction patterns and energy spectrum measures is introduced along with a systematic comparison of the zeroth-order energy spectrum main features for BACs belonging to different spectral classes, including Fibonacci-class, precious means, metallic means, mixed means and period doubling based representatives. These systems are described by means of mixed-type Hamiltonians which include both diagonal and off-diagonal terms aperiodically distributed. An algebraic approach highlighting chemical correlation effects present in the underlying lattice is introduced. Close analytical expressions are obtained by exploiting some algebraic properties of suitable blocking schemes preserving the atomic order of the original lattice. The existence of a resonance energy which defines the basic anatomy of the zeroth-order energy spectra structure for the standard Fibonacci, the precious means and the Fibonacci-class quasicrystals is disclosed. This eigenstate is also found in the energy spectra of BACs belonging to other spectral classes, but for specific particular choices of the corresponding model parameters only. The transmission coefficient of these resonant states is always bounded below, although their related Landauer conductance values may range from highly conductive to highly resistive ones, depending on the relative strength of the chemical bonds.A spectral classification of general one-dimensional binary aperiodic crystals based on both their diffraction and energy spectrum measures is introduced, along with an algebraic approach highlighting chemical correlation effects in the underlying lattice. A number of resonant energies, shared by systems belonging to different spectral classes, are disclosed. Their related Landauer conductance takes on either highly conductive or highly resistive values, depending on the relative strength of the chemical bonds.
PubDate: 2017-07-17T03:30:52.700763-05:
DOI: 10.1002/andp.201700079
- Authors: Enrique Maciá
- Quantum Kinetic Theory of a Massless Scalar Model in the Presence of a
Schwarzschild Black Hole- Authors: Slava Emelyanov
Abstract: We employ quantum kinetic theory to investigate local quantum physics in the background of spherically symmetric and neutral black holes formed through the gravitational collapse. For this purpose in mind, we derive and study the covariant Wigner distribution function W(x,p) near to and far away from the black-hole horizon. We find that the local density of the particle number is negative in the near-horizon region, while the entropy density is imaginary. These pose a question whether kinetic theory is applicable in the near-horizon region. We elaborate on that and propose a possible interpretation of how this result might nevertheless be self-consistently understood.Classical many-particle systems can be described with the help of macroscopic state variables: energy density, pressure, particle number density and so on. The authors employ relativistic kinetic theory to study local state variables in the background of an evaporating black hole. For that purpose, a distribution function characterising the black-hole evaporation is derived in the far-from- and near-horizon region. It is then used to examine local quantum physics of black holes. The authors find new results which shed light on microscopic nature of the evaporation process.
PubDate: 2017-07-17T03:30:29.028799-05:
DOI: 10.1002/andp.201700078
- Authors: Slava Emelyanov
- Three-Phonon and Four-Phonon Interaction Processes in a Pair-Condensed
Fermi Gas- Authors: H. Kurkjian; Y. Castin, A. Sinatra
Abstract: We study the interactions among phonons and the phonon lifetime in a pair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime. To compute the phonon-phonon coupling amplitudes we use a microscopic model based on a generalized BCS Ansatz including moving pairs, which allows for a systematic expansion around the mean field BCS approximation of the ground state. We show that the quantum hydrodynamic expression of the amplitudes obtained by Landau and Khalatnikov apply only on the energy shell, that is for resonant processes that conserve energy. The microscopic model yields the same excitation spectrum as the Random Phase Approximation, with a linear (phononic) start and a concavity at low wave number that changes from upwards to downwards in the BEC-BCS crossover. When the concavity of the dispersion relation is upwards at low wave number, the leading damping mechanism at low temperature is the Beliaev-Landau process 2 phonons 1 phonon while, when the concavity is downwards, it is the Landau-Khalatnikov process 2 phonons 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependence on the interaction strength, we obtain a universal formula for the damping rate. This universal formula corrects and extends the original analytic results of Landau and Khalatnikov [ZhETF 19, 637 (1949)] for the 22 processes in the downward concavity case. In the upward concavity case, for the Beliaev 1 2 process for the unitary gas at zero temperature, we calculate the damping rate of an excitation with wave number q including the first correction proportional to q7 to the q5 hydrodynamic prediction, which was never done before in a systematic way.Low temperature phonon damping rates in an unpolarised spin-1/2 superfluid Fermi gas are calculated in the collisionless regime for any interaction strength across the BEC-BCS crossover. Close to unitarity the leading damping mechanism changes from the three-phonon Beliaev-Landau to the yet unobserved four-phonon Landau-Khalatnikov damping. The 1949 Landau and Khalatnikov calculation is corrected and extended. At unitarity at zero temperature the first correction to the Beliaev damping rate is obtained.
PubDate: 2017-07-13T06:31:45.629842-05:
DOI: 10.1002/andp.201600352
- Authors: H. Kurkjian; Y. Castin, A. Sinatra
- Review of the Theoretical Description of Time-Resolved Angle-Resolved
Photoemission Spectroscopy in Electron-Phonon Mediated Superconductors- Authors: A. F. Kemper; M. A. Sentef, B. Moritz, T. P. Devereaux, J. K. Freericks
Abstract: We review recent work on the theory for pump/probe photoemission spectroscopy of electron-phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal-Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson-Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity.This paper reviews work on nonequilibrum dynamical mean-field theory for superconductors emphasizing different phenomena that can be observed in photoemission.
PubDate: 2017-07-13T05:52:53.539043-05:
DOI: 10.1002/andp.201600235
- Authors: A. F. Kemper; M. A. Sentef, B. Moritz, T. P. Devereaux, J. K. Freericks
- Charge-Carrier Transport in Large-Area Epitaxial Graphene
- Authors: Ferdinand Kisslinger; Matthias Popp, Johannes Jobst, Sam Shallcross, Heiko B. Weber
Abstract: We present an overview of recent charge carrier transport experiments in both monolayer and bilayer graphene, with emphasis on the phenomena that appear in large-area samples. While many aspects of transport are based on quantum mechanical concepts, in the large-area limit classical corrections dominate and shape the magnetoresistance and the tunneling conductance. The discussed phenomena are very general and can, with little modification, be expected in any atomically thin 2D conductor.The authors present an overview of recent charge carrier transport experiments in both monolayer and bilayer graphene, with emphasis on the phenomena that appear in large-area samples. In the large-area limit classical corrections dominate and shape the magnetoresistance and the tunneling conductance. The discussed phenomena are very general and can, with little modification, be expected in any atomically thin 2D conductor.
PubDate: 2017-07-13T05:52:23.636001-05:
DOI: 10.1002/andp.201700048
- Authors: Ferdinand Kisslinger; Matthias Popp, Johannes Jobst, Sam Shallcross, Heiko B. Weber
- Quantum Transport in the Black-Hole Configuration of an Atom Condensate
Outcoupled Through an Optical Lattice- Authors: J. R. M. Nova; F. Sols, I. Zapata
Abstract: The outcoupling of a Bose-Einstein condensate through an optical lattice provides an interesting scenario to study quantum transport phenomena or the analog Hawking effect as the system can reach a quasi-stationary black-hole configuration. We devote this work to characterize the quantum transport properties of quasi-particles on top of this black-hole configuration by computing the corresponding scattering matrix. We find that most of the features can be understood in terms of the usual Schrödinger scattering. In particular, a transmission band appears in the spectrum, with the normal-normal transmission dominating over the anomalous-normal one. We show that this picture still holds in a realistic experimental situation where the actual Gaussian envelope of the optical lattice is considered. A peaked resonant structure is displayed near the upper end of the transmission band, which suggests that the proposed setup is a good candidate to provide a clear signal of spontaneous Hawking radiation.Due to its high quasi-stationarity, the analog black-hole resulting from the outcoupling of a condensate through an optical lattice is an optimal scenario for studying quantum transport phenomena, including the analog of Hawking radiation. This work presents a study of the associated quasi-particle spectrum. The Hawking spectrum shows a highly non-thermal behavior whenever the top of the conduction band is below the threshold frequency, which could ease its detection.
PubDate: 2017-07-13T05:51:10.894926-05:
DOI: 10.1002/andp.201600385
- Authors: J. R. M. Nova; F. Sols, I. Zapata
- Invariant-Based Pulse Design for Three-Level Systems Without the
Rotating-Wave Approximation- Authors: Yi-Hao Kang; Ye-Hong Chen, Bi-Hua Huang, Jie Song, Yan Xia
Abstract: In this paper, a scheme is put forward to design pulses which drive a three-level system based on the reverse engineering with Lewis-Riesenfeld invariant theory. The scheme can be applied to a three-level system even when the rotating-wave approximation (RWA) can not be used. The amplitudes of pulses and the maximal values of detunings in the system could be easily controlled by adjusting control parameters. We analyze the dynamics of the system by an invariant operator, so additional couplings are unnecessary. Moreover, the approaches to avoid singularity of pulses are studied and several useful results are obtained. We hope the scheme could contribute to fast quantum information processing without RWA.The authors have proposed a scheme that design feasible pulses for fast manipulation of a three-level quantum system without using the the rotating-wave approximation. By analysis dynamics of the system via a new found Lewis-Riesenfeld invariant, the authors have given three approaches to design pulses, which could be smoothly turned on and turned off, and whose amplitudes could be easily controlled. Besides, no extra couplings are required in the scheme.
PubDate: 2017-07-12T03:05:37.548632-05:
DOI: 10.1002/andp.201700004
- Authors: Yi-Hao Kang; Ye-Hong Chen, Bi-Hua Huang, Jie Song, Yan Xia
- Modelling Spatial Variations of the Speed of Light
- Authors: Adam Balcerzak; Mariusz P. Da̧browski, Vincenzo Salzano
Abstract: We extend a new method to measure possible variation of the speed of light by using Baryon Acoustic Oscillations and the Hubble function onto an inhomogeneous pressure model of the universe. The method relies on the fact that there is a simple relation between the angular diameter distance (DA) maximum and the Hubble function (H) evaluated at the same maximum-condition redshift, which includes the speed of light c. One limit of such a method was the assumption of the vanishing of spatial curvature (though, as it has been shown, a non-zero curvature has negligible effect). In this paper, apart from taking into account an inhomogeneity, we consider non-zero spatial curvature and calculate an exact relation between DA and H. Our main result is the evaluation if current or future missions such as Square Kilometer Array (SKA) can be sensitive enough to detect any spatial variation of c which can in principle be related to the recently observed spatial variation of the fine structure constant (an effect known as α-dipole).The authors extend their method of cosmic rulers and cosmic clocks to check for spatial variations of the speed of light c. A specific model from the class of inhomogeneous Stephani cosmological models is proposed. It agrees with cosmological data from Type Ia Supernovae, Baryon Acoustic Oscillations, Cosmic Microwave Background, and Hubble parameter. The spatial variability of c has the merit of being falsifiable by SKA (Square Kilometer Array) mission.
PubDate: 2017-07-12T03:05:23.313558-05:
DOI: 10.1002/andp.201600409
- Authors: Adam Balcerzak; Mariusz P. Da̧browski, Vincenzo Salzano
- Protecting Quantum State in Time-Dependent Decoherence-Free Subspaces
Without the Rotating-Wave Approximation- Authors: Qi-Cheng Wu; Ye-Hong Chen, Bi-Hua Huang, Zhi-Cheng Shi, Jie Song, Yan Xia
Abstract: In this paper, we propose a scheme to protect quantum state by utilizing the time-dependent decoherence-free subspaces (TDFSs) theory without the rotating-wave approximation (RWA). A coherent control is designed to drive the quantum system into the TDFSs, moreover, the singularities of the designed coherent control can be avoided by appropriately choosing the control parameters. From an experimental view point, the influences of variations of the control parameters and the imperfect initial state are discussed in detail. Numerical simulations confirm that the scheme can protect the quantum information from both the environmental decoherence and the control errors. In addition, by comparing with the scheme employing RWA, we show that the weak coherent control field is not suitable to create the TDFS, the counter-rotating terms in the strong coherent control are helpful to protect the quantum information.The work addresses a long-standing problem of protecting quantum system: when the rotating-wave approximation (RWA) breaks down, how can we protect the quantum information from both the environmental decoherence and the control errors by utilizing coherent control' The authors demonstrate the possibility to drive a two-level system without RWA protecting the purity of the quantum state in an environment that in principle induces decoherence.
PubDate: 2017-07-12T01:35:36.033017-05:
DOI: 10.1002/andp.201700186
- Authors: Qi-Cheng Wu; Ye-Hong Chen, Bi-Hua Huang, Zhi-Cheng Shi, Jie Song, Yan Xia
- Time Asymmetric Quantum Mechanics and Shock Waves: Exploring the
Irreversibility in Nonlinear Optics- Authors: Giulia Marcucci; Maria Chiara Braidotti, Silvia Gentilini, Claudio Conti
Abstract: The description of irreversible phenomena is a still debated topic in quantum mechanics. Still nowadays, there is no clear procedure to distinguish the coupling with external baths from the intrinsic irreversibility in isolated systems. In 1928 Gamow introduced states with exponentially decaying observables not belonging to the conventional Hilbert space. These states are named Gamow vectors, and they belong to rigged Hilbert spaces. This review summarizes the contemporary approach using Gamow vectors and rigged Hilbert space formalism as foundations of a generalized “time asymmetric” quantum mechanics. We study the irreversible propagation of specific wave packets and show that the topic is surprisingly related to the problem of irreversibility of shock waves in classical nonlinear evolution. We specifically consider the applications in the field of nonlinear optics. We show that it is possible to emulate irreversible quantum mechanical process by the nonlinear evolution of a laser beam and we provide experimental tests by the generation of dispersive shock waves in highly nonlocal regimes. We demonstrate experimentally the quantization of decay rates predicted by the time-asymmetric quantum mechanics. This work furnishes support to the idea of intrinsically irreversible wave propagation, and to novel tests of the foundations of quantum mechanics.In 1928 Gamow introduced states with exponentiallydecaying observables belonging to a rigged Hilbert space: the Gamow vectors (GVs). In this review, the contemporary approach using GVs as foundations of the “time asymmetric” quantum mechanics, and its relation with the problem of irreversibility of shock waves in classical nonlinear evolution are shown. The optical dispersive wave breaking in highly nonlocal regimes emulates an irreversible quantum mechanical process, experimentally proved.
PubDate: 2017-07-11T06:02:31.622134-05:
DOI: 10.1002/andp.201600349
- Authors: Giulia Marcucci; Maria Chiara Braidotti, Silvia Gentilini, Claudio Conti
- Broadband Terahertz Polarization Converter and Asymmetric Transmission
Based on Coupled Dielectric-Metal Grating- Authors: Shi-Tong Xu; Fu-Tai Hu, Meng Chen, Fei Fan, Sheng-Jiang Chang
Abstract: Coupled dielectric-metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high-efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission.Terahertz (THz) polarization converter has an irreplaceable role in manipulating the polarization states of the THz waves. Here, a coupled dielectric-metal grating is proposed for broadband THz wave polarization conversion and asymmetric transmission, which is composed of subwavelength Si deep relief grating and gold wire grating on the two surfaces of a Si substrate. The results show that a broadband asymmetric transmission is achieved with an extinction ratio of 30dB from 0.2 to 1.2 THz and the highest polarization conversion of 90% can be obtained.
PubDate: 2017-07-11T06:01:58.289107-05:
DOI: 10.1002/andp.201700151
- Authors: Shi-Tong Xu; Fu-Tai Hu, Meng Chen, Fei Fan, Sheng-Jiang Chang
- Three-Dimensional, Time-Resolved Profiling of Ferroelectric Domain Wall
Dynamics by Spectral-Domain Optical Coherence Tomography- Authors: Alexander Haußmann; Lars Kirsten, Sebastian Schmidt, Peter Cimalla, Lukas Wehmeier, Edmund Koch, Lukas M. Eng
Abstract: We apply here spectral-domain optical coherence tomography (SD-OCT) for the precise detection and temporal tracking of ferroelectric domain walls (DWs) in magnesium-doped periodically poled lithium niobate (Mg:PPLN). We reproducibly map static DWs at an axial (depth) resolution down to ∼ 0.6 μm, being located up to 0.5 mm well inside the single crystalline Mg:PPLN sample. We show that a full 3-dimensional (3D) reconstruction of the DW geometry is possible from the collected data, when applying a special algorithm that accounts for the nonlinear optical dispersion of the material. Our OCT investigation provides valuable reference information on the DWs’ polarization charge distribution, which is known to be the key to the electrical conductivity of ferroelectric DWs in such systems. Hence, we carefully analyze the SD-OCT signal dependence both when varying the direction of incident polarization, and when applying electrical fields along the polar axis. Surprisingly, the large backreflection intensities recorded under extraordinary polarization are not affected by any electrical field, at least for field strengths below the switching threshold, while no significant signals above noise floor are detected under ordinary polarization. Finally, we employed the high-speed SD-OCT setup for the real-time DW tracking upon ferroelectric domain switching under high external fields.Optical coherence tomography, known for its superb imaging qualities in biomedicine, can also be applied for the precise three-dimensional mapping and temporal tracking of ferroelectric domain walls. This opens up new possibilities for the comprehensive geometrical characterization of such walls, which is a prerequisite for the thorough investigation of electrical domain wall conductivity in ferroelectrics.
PubDate: 2017-07-10T04:37:45.890738-05:
DOI: 10.1002/andp.201700139
- Authors: Alexander Haußmann; Lars Kirsten, Sebastian Schmidt, Peter Cimalla, Lukas Wehmeier, Edmund Koch, Lukas M. Eng
- Unveiling the Link Between Fractional SchrÃ¶dinger Equation and Light
Propagation in Honeycomb Lattice- Authors: Da Zhang; Yiqi Zhang, Zhaoyang Zhang, Noor Ahmed, Yanpeng Zhang, Fuli Li, Milivoj R. Belić, Min Xiao
Abstract: We suggest a real physical system — the honeycomb lattice — as a possible realization of the fractional Schrödinger equation (FSE) system, through utilization of the Dirac-Weyl equation (DWE). The fractional Laplacian in FSE causes modulation of the dispersion relation of the system, which becomes linear in the limiting case. In the honeycomb lattice, the dispersion relation is already linear around the Dirac point, suggesting a possible connection with the FSE, since both models can be reduced to the one described by the DWE. Thus, we propagate Gaussian beams in three ways: according to FSE, honeycomb lattice around the Dirac point, and DWE, to discover universal behavior — the conical diffraction. However, if an additional potential is brought into the system, the similarity in behavior is broken, because the added potential serves as a perturbation that breaks the translational periodicity of honeycomb lattice and destroys Dirac cones in the dispersion relation.The fractional Schrödinger equation (FSE) is the fundamental equation of the fractional quantum mechanics. The fractional Laplacian in FSE causes a modulation of the dispersion relation of the system, which becomes linear in the limiting case. This change brings profound differences in the behavior of the wave function. Here, the authors compare the similarities between evolution described by FSE, evolution in honeycomb lattice described by usual Schrödinger equation, and find that the connection can be established via the Dirac-Weyl equation.
PubDate: 2017-07-10T04:37:03.41991-05:0
DOI: 10.1002/andp.201700149
- Authors: Da Zhang; Yiqi Zhang, Zhaoyang Zhang, Noor Ahmed, Yanpeng Zhang, Fuli Li, Milivoj R. Belić, Min Xiao
- Fast and Robust Quantum Information Transfer in Annular and Radial
Superconducting Networks- Authors: Yi-Hao Kang; Zhi-Cheng Shi, Bi-Hua Huang, Jie Song, Yan Xia
Abstract: In this paper, we propose a protocol to achieve fast and robustness quantum information transfer (QIT) in annular and radial superconducting networks, where each quantum node is composed of a superconducting quantum interference device (SQUID) inside a coplanar waveguide resonator (CPWR). The process is based on reversely constructing time-dependent control Hamiltonian by designing evolution operator. With the protocol, the maximal population of lossy intermediate states and the amplitudes of pulses can be easily controlled by two corresponding control parameters. Therefore, one can design feasible pulses for QIT with great flexibility. Besides, the speed of the QIT here is much faster compared with that with adiabatic QIT. Moreover, numerical simulations show that the protocol still possesses high fidelity when lossy factors and imperfect operations are taken into account. Therefore, the protocol may provide a useful way to manipulate quantum information networks.The authors have proposed a protocol to achieve fast and robustness quantum information transfer (QIT) in annular and radial superconducting networks. Based on the method, which reversely constructs time-dependent control Hamiltonian by designing evolution operator, QIT in referenced superconducting networks are much faster than adiabatic QIT. Moreover, numerical simulations show that the protocol still possesses high fidelity when lossy factors and imperfect operations are taken into account.
PubDate: 2017-07-10T04:36:53.597116-05:
DOI: 10.1002/andp.201700154
- Authors: Yi-Hao Kang; Zhi-Cheng Shi, Bi-Hua Huang, Jie Song, Yan Xia
- Ray Modes in Random Gap Systems
- Authors: K. Ziegler
Abstract: A disordered photonic crystal with spectral degeneracies in the form of Dirac nodes is considered. Disorder can create a random gap at the Dirac nodes, which leads to the formation of random edge modes. We study the distribution of these edge modes and find from symmetry considerations that the discrete anisotropy of the photonic crystal is spontaneously broken for the propagation of photons from a local photon source. This effect can be understood as the spontaneous creation of a ray mode or as the creation of a one-dimensional waveguide in a two-dimensional photonic crystal through strong random scattering. The phenomenon must be distinguished from Anderson localization of photons in a single band crystal and can be considered as angular localization, since it creates geometric states rather than confining the photons to an area of the size of the localization length. The propagation of the photon intensity is described by a Fokker-Planck equation, whose drift term is determined by the spectrum of the photonic crystal near the Dirac node.A photonic crystal with two bands and a Dirac node is considered. Random photonic edge states are created by adding a random Dirac mass, as it has been discussed for photonic metamaterials. The corresponding average photon intensity, generated by a local source at the center of the system, can escape from Anderson localization even for strong random scattering. This effect is understood as ray mode formation by angular localization.
PubDate: 2017-07-10T04:36:19.4679-05:00
DOI: 10.1002/andp.201600345
- Authors: K. Ziegler
- Hamiltonian Ratchets with Ultra-Cold Atoms
- Authors: Jiating Ni; Siamak Dadras, Wa Kun Lam, Rajendra K. Shrestha, Mark Sadgrove, Sandro Wimberger, Gil S. Summy
Abstract: Quantum-resonance ratchets have been realized over the last ten years for the production of directed currents of atoms. These non-dissipative systems are based on the interaction of a Bose-Einstein condensate with an optical standing wave potential to produce a current of atoms in momentum space. In this paper we provide a review of the important features of these ratchets with a particular emphasis on their optimization using more complex initial states. We also examine their stability close to resonance conditions of the kicking. Finally we discuss the way in which these ratchets may pave the way for applications in quantum (random) walks and matter-wave interferometry.Quantum-resonance ratchets have been realized over the last ten years for the production of directed currents of matter waves. These non-dissipative systems are based on the interaction of a Bose-Einstein condensate with an optical standing wave potential to produce a current in momentum space. A review of these ratchets is given with a particular emphasis on their optimization and stability, both of which are needed for applications.
PubDate: 2017-07-07T05:56:46.926425-05:
DOI: 10.1002/andp.201600335
- Authors: Jiating Ni; Siamak Dadras, Wa Kun Lam, Rajendra K. Shrestha, Mark Sadgrove, Sandro Wimberger, Gil S. Summy
- Terahertz Electric Field Driven Electric Currents and Ratchet Effects in
Graphene- Authors: Sergey D. Ganichev; Dieter Weiss, Jonathan Eroms
Abstract: Terahertz field induced photocurrents in graphene were studied experimentally and by microscopic modeling. Currents were generated by cw and pulsed laser radiation in large area as well as small-size exfoliated graphene samples. We review general symmetry considerations leading to photocurrents depending on linear and circular polarized radiation and then present a number of situations where photocurrents were detected. Starting with the photon drag effect under oblique incidence, we proceed to the photogalvanic effect enhancement in the reststrahlen band of SiC and edge-generated currents in graphene. Ratchet effects were considered for in-plane magnetic fields and a structure inversion asymmetry as well as for graphene with non-symmetric patterned top gates. Lastly, we demonstrate that graphene can be used as a fast, broadband detector of terahertz radiation.The authors review experimental and theoretical studies of photocurrents driven by polarized terahertz radiation in graphene. The phenomenological and microscopic theory of various second order phenomena and the state-of-the-art of the experiments are discussed. They show that nonlinear transport opens up new opportunities for probing helical Dirac electron states, address prospectives of theoretical and experimental studies and discuss the application of structured graphene for fast room temperature detection of THz radiation.
PubDate: 2017-07-07T05:56:31.378606-05:
DOI: 10.1002/andp.201600406
- Authors: Sergey D. Ganichev; Dieter Weiss, Jonathan Eroms
- Physics of Quantum Light Emitters in Disordered Photonic Nanostructures
- Authors: P. D. García; P. Lodahl
Abstract: Nanophotonics focuses on the control of light and the interaction with matter by the aid of intricate nanostructures. Typically, a photonic nanostructure is carefully designed for a specific application and any imperfections may reduce its performance, i.e., a thorough investigation of the role of unavoidable fabrication imperfections is essential for any application. However, another approach to nanophotonic applications exists where fabrication disorder is used to induce functionalities by enhancing light-matter interaction. Disorder leads to multiple scattering of light, which is the realm of statistical optics where light propagation requires a statistical description. We review here the recent progress on disordered photonic nanostructures and the potential implications for quantum photonics devices.The development of nanoscale optical devices requires high quality nanocavities to mediate the optical feedback. Any fabrication method will generate imperfections that may induce light loss limiting the device performance. However, in some cases such disorder may enable new functionalities. Here, the authors review unconventional nanostructures where disorder enables highly efficient light-matter interaction.
PubDate: 2017-07-07T05:42:07.790209-05:
DOI: 10.1002/andp.201600351
- Authors: P. D. García; P. Lodahl
- Large-Scale Modulation of Left-Handed Passband in Hybrid
Graphene/Dielectric Metasurface- Authors: Chuanbao Liu; Yang Bai, Ji Zhou, Qian Zhao, Lijie Qiao
Abstract: Large-scale modulation of the left-handed transmission with a high quality factor is greatly desired by high-performance optical devices, but the requirements are hard to be satisfied simultaneously. This paper presents a hybrid graphene/dielectric metasurface to realize a large transmission modulation for the left-handed passband at near-infrared frequencies via tuning the Fermi energy of graphene. By splitting the nanoblocks, i.e. introducing an additional symmetry breaking in the unit cell, the metasurface demonstrates an ultrahigh quality factor (Q ≈ 550) of Fano resonance with near-unity transmission and full 2π phase coverage due to the interference between Mie-type magnetic and electric resonances, which induces the negative refraction property. Besides, the split in the nanoblock greatly enhances the local field by increasing the critical coupling area, so the light-graphene interaction is promoted intensively. When the surface conductivity of graphene is electrically tuned, the hybrid graphene/dielectric metasurface exhibits a deep modulation of 85% for the left-handed passband, which is robust even for the highest loss of graphene. Moreover, the simple configuration remarkably reduces the fabrication requirements to facilitate the widespread applications.Large-scale modulation of the left-handed passband with a high quality factor is demonstrated in the hybrid graphene/dielectric metasurface at near-infrared frequencies. By splitting the nanoblocks, the metasurface shows a near-unity transmission with full phase coverage. The greatly enhanced local field at surface offers a platform to coupling with graphene and produces a deep modulation of 85% for the left-handed passband.
PubDate: 2017-07-07T05:40:37.267218-05:
DOI: 10.1002/andp.201700125
- Authors: Chuanbao Liu; Yang Bai, Ji Zhou, Qian Zhao, Lijie Qiao
- Classical Bifurcation Diagrams by Quantum Means
- Authors: Mikhail V. Ivanchenko; Eugene A. Kozinov, Valentin D. Volokitin, Alexey V. Liniov, Iosif B. Meyerov, Sergey V. Denisov
Abstract: Asymptotic state of an open quantum system may change substantially upon variations of system parameters. These changes can be often identified as bifurcation transitions in the classical mean-filed equations describing evolution of the relevant observables. We demonstrate that these bifurcations can be made visible as changes in the structure of the asymptotic density matrix of the original quantum system. By using an N-boson dimer, we present quantum ‘bifurcation diagrams’ for the pitchfork and saddle-node bifurcations (in the stationary dimer) and visualize a period-doubling transition to chaos (in a periodically modulated dimer).Asymptotic state of an open quantum system can change substantually with system parameters, exhibiting ‘quantum bifurcations’. Their regular and chaotic counterparts in the corresponding classical mean-filed equations, can be made visible and matched with changes in the structure of the asymptotic density matrix of the original quantum system, as our study reveals.
PubDate: 2017-07-07T04:22:04.138691-05:
DOI: 10.1002/andp.201600402
- Authors: Mikhail V. Ivanchenko; Eugene A. Kozinov, Valentin D. Volokitin, Alexey V. Liniov, Iosif B. Meyerov, Sergey V. Denisov
- Hydrodynamic Approach to Electronic Transport in Graphene
- Authors: Boris N. Narozhny; Igor V. Gornyi, Alexander D. Mirlin, Jörg Schmalian
Abstract: The last few years have seen an explosion of interest in hydrodynamic effects in interacting electron systems in ultra-pure materials. In this paper we briefly review the recent advances, both theoretical and experimental, in the hydrodynamic approach to electronic transport in graphene, focusing on viscous phenomena, Coulomb drag, non-local transport measurements, and possibilities for observing nonlinear effects.The last few years have seen an explosion of interest in hydrodynamic effects in interacting electron systems in ultra-pure materials. This paper reviews the recent advances, both theoretical and experimental, in the hydrodynamic approach to electronic transport in graphene, focusing on viscous phenomena, Coulomb drag, non-local transport measurements, and possibilities for observing nonlinear effects.
PubDate: 2017-07-07T04:21:36.423926-05:
DOI: 10.1002/andp.201700043
- Authors: Boris N. Narozhny; Igor V. Gornyi, Alexander D. Mirlin, Jörg Schmalian
- Slow and Stopped Light in Active Gain Composite Materials of Metal
Nanoparticles: Ultralarge Group Index-Bandwidth Product Predicted- Authors: Kwang-Hyon Kim; Song-Hyok Choe
Abstract: Chip-compatible slow light devices with large group index-bandwidth products and low losses are of great interest in the community of modern photonics. In this work, active gain materials containing metal nanoparticles are proposed as the slow and stopped light materials. Gain-assisted high field enhancement in metal nanoparticles and the resultant strong dispersion lead to such phenomena. From the Maxwell-Garnett model, it is revealed that the metal nanocomposite exhibits the infinitely large group index when the gain of the host medium and the filling factor of metal nanoparticles satisfy a critical condition. For the gain of the host above the critical value, one can observe slowing down effect with amplification of light pulses. Significantly large group index-bandwidth products, which vary from a few to several thousand or even infinity depending on the gain value of the host medium, have been numerically predicted in active silica glasses containing spheroidal metal nanoparticles, as examples. The proposed scheme inherently provides the widely varying operating spectral range by changing the aspect ratio of metal nanoparticles and chip-compatibility with low cost.Active gain materials containing metal nanoparticles are proposed as slow and stopped light materials. Gain-assisted high field enhancement in metal nanoparticles and the resultant strong dispersion lead to such phenomena. For the gain of the host medium above critical value, one can observe slowing down effect with amplification of light pulses. Significantly large group index-bandwidth products from a few to several thousand or even infinity have been predicted.
PubDate: 2017-07-06T10:58:29.810283-05:
DOI: 10.1002/andp.201700103
- Authors: Kwang-Hyon Kim; Song-Hyok Choe
- Low Resistive Edge Contacts to CVD-Grown Graphene Using a CMOS Compatible
Metal- Authors: Mehrdad Shaygan; Martin Otto, Abhay A. Sagade, Carlos A. Chavarin, Gerd Bacher, Wolfgang Mertin, Daniel Neumaier
Abstract: The exploitation of the excellent intrinsic electronic properties of graphene for device applications is hampered by a large contact resistance between the metal and graphene. The formation of edge contacts rather than top contacts is one of the most promising solutions for realizing low ohmic contacts. In this paper the fabrication and characterization of edge contacts to large area CVD-grown monolayer graphene by means of optical lithography using CMOS compatible metals, i.e. Nickel and Aluminum is reported. Extraction of the contact resistance by Transfer Line Method (TLM) as well as the direct measurement using Kelvin Probe Force Microscopy demonstrates a very low width specific contact resistance down to 130 Ωμm. The contact resistance is found to be stable for annealing temperatures up to 150°C enabling further device processing. Using this contact scheme for edge contacts, a field effect transistor based on CVD graphene with a high transconductance of 0.63 mS/μm at 1 V bias voltage is fabricated.In this work, the authors report on the fabrication of edge contacts to large area CVD monolayer graphene using a CMOS compatible metal with a very low contact resistance. The improved contacting scheme enables the realization of high performance graphene devices.
PubDate: 2017-07-05T12:32:35.88435-05:0
DOI: 10.1002/andp.201600410
- Authors: Mehrdad Shaygan; Martin Otto, Abhay A. Sagade, Carlos A. Chavarin, Gerd Bacher, Wolfgang Mertin, Daniel Neumaier
- Advisory Board
- PubDate: 2017-07-05T05:49:06.392634-05:
DOI: 10.1002/andp.201770052
- PubDate: 2017-07-05T05:49:06.392634-05:
- Contents: Ann. Phys. 7'2017
- PubDate: 2017-07-05T05:49:05.056122-05:
DOI: 10.1002/andp.201770053
- PubDate: 2017-07-05T05:49:05.056122-05:
- Issue Information: Ann. Phys. 7'2017
- PubDate: 2017-07-05T05:49:04.399052-05:
DOI: 10.1002/andp.201770051
- PubDate: 2017-07-05T05:49:04.399052-05:
- Editorial
- Authors: Jens H. Bardarson; Frank Pollmann, Ulrich Schneider, Shivaji Sondhi
PubDate: 2017-07-05T05:49:02.562281-05:
DOI: 10.1002/andp.201700191
- Authors: Jens H. Bardarson; Frank Pollmann, Ulrich Schneider, Shivaji Sondhi
- Cover Picture: Ann. Phys. 7'2017
- Abstract: Many-body localization generalizes Anderson localization to interacting systems and entails a disorder induced breakdown of ergodicity and thermalization. The figure illustrates a system of interacting particles exposed to a disordered potential. As the disorder strength is tuned, an interaction-driven, dynamical phase transition from an extended to a many-body-localized phase occurs.
PubDate: 2017-07-05T05:48:58.518664-05:
DOI: 10.1002/andp.201770050
- Abstract: Many-body localization generalizes Anderson localization to interacting systems and entails a disorder induced breakdown of ergodicity and thermalization. The figure illustrates a system of interacting particles exposed to a disordered potential. As the disorder strength is tuned, an interaction-driven, dynamical phase transition from an extended to a many-body-localized phase occurs.
- Recent progress in many-body localization
- Authors: Dmitry A. Abanin; Zlatko Papić
Abstract: This article is a brief introduction to the rapidly evolving field of many-body localization. Rather than giving an in-depth review of the subject, our aspiration here is simply to introduce the problem and its general context, outlining a few directions where notable progress has been achieved in recent years. We hope that this will prepare the readers for the more specialized articles appearing in this dedicated Volume of Annalen der Physik, where these developments are discussed in more detail.Many-body localization can occur in isolated, interacting quantum systems with strong quenched disorder. Many-body localized systems are different from the more common ergodic systems in that they fail to reach thermal equilibrium at long times. Instead, these systems are characterized by the absence of transport, similar to non-interacting Anderson insulators, and have novel dynamical and entanglement properties. This article is a brief overview of the recent theoretical and experimental progress in this active field of research featured in this special volume of Annalen der Physik.
PubDate: 2017-07-05T05:48:56.163159-05:
DOI: 10.1002/andp.201700169
- Authors: Dmitry A. Abanin; Zlatko Papić
- Anderson Localization for Very Strong Speckle Disorder
- Authors: M. Hilke; H. Eleuch
Abstract: We evaluate the localization length of the wave (or Schrödinger) equation in the presence of a disordered speckle potential. This is relevant for experiments on cold atoms in optical speckle potentials. We focus on the limit of large disorder, where the Born approximation breaks down and derive an expression valid in the “quasi-metallic” phase at large disorder. This phase becomes strongly localized and the effective mobility edge disappears.The authors evaluate the localization length of the wave (or Schrödinger) equation in the presence of a disordered speckle potential. This is relevant for experiments on cold atoms in optical speckle potentials. The authors focus on the limit of large disorder, where the Born approximation breaks down and derive an expression based on a non-linear approximation valid in the “quasi-metallic” phase at large disorder. The picture shows an example of the amplitude (ln ψ ) of the wave solution as a function of position for a very strong speckle potential, which has several tunneling regions.
PubDate: 2017-07-04T11:23:33.778577-05:
DOI: 10.1002/andp.201600347
- Authors: M. Hilke; H. Eleuch
- Electronic Transport Properties of 1D-Defects in Graphene and Other
2D-Systems- Authors: P. Willke; M. A. Schneider, M. Wenderoth
Abstract: The continuous progress in device miniaturization demands a thorough understanding of the electron transport processes involved. The influence of defects - discontinuities in the perfect and translational invariant crystal lattice - plays a crucial role here. For graphene in particular, they limit the carrier mobility often demanded for applications by contributing additional sources of scattering to the sample. Due to its two-dimensional nature graphene serves as an ideal system to study electron transport in the presence of defects, because one-dimensional defects like steps, grain boundaries and interfaces are easy to characterize and have profound effects on the transport properties. While their contribution to the resistance of a sample can be extracted by carefully conducted transport experiments, scanning probe methods are excellent tools to study the influence of defects locally. In this letter, the authors review the results of scattering at local defects in graphene and other 2D systems by scanning tunneling potentiometry, 4-point-probe microscopy, Kelvin probe force microscopy and conventional transport measurements. Besides the comparison of the different defect resistances important for device fabrication, the underlying scattering mechanisms are discussed giving insight into the general physics of electron scattering at defects.In this review the recent research on local electron transport across extended, one-dimensional defects in graphene using scanning probe methods is summarized. In particular substrate steps, wrinkles, stacking faults, monolayer/bilayer-interfaces, collapsed wrinkles and grain boundaries are discussed. While these defects can have a significant influence on the total resistance of a sample they also help to shed light on the general physics of electron scattering at defects and the underlying scattering mechanisms.
PubDate: 2017-07-04T11:22:50.881735-05:
DOI: 10.1002/andp.201700003
- Authors: P. Willke; M. A. Schneider, M. Wenderoth
- Quantum Ratchet in Disordered Quantum Walk
- Authors: Sagnik Chakraborty; Arpan Das, Arindam Mallick, C. M. Chandrashekar
Abstract: Symmetrically evolving discrete quantum walk results in dynamic localization with zero mean displacement when the standard evolution operations are replaced by a temporal disorder evolution operation. In this work we show that the quantum ratchet action, that is, a directed transport in standard or disordered discrete-time quantum walk can be realized by introducing a pawl like effect realized by using a fixed coin operation at marked positions that is, different from the ones used for evolution at other positions. We also show that the combination of standard and disordered evolution operations can be optimized to get the mean displacement of order ∝ t (number of walk steps). This model of quantum ratchet in quantum walk is defined using only a set of entangling unitary operators resulting in the coherent quantum transport.Introducing pawl like effect in position space breaks the spatial symmetry in the position space of the quantum walk system introducing a quantum ratchet effect. In this figure the probability distribution after 100 steps of quantum walk with pawl effect using different combination of evolution operators is shown. Transport of wavepacket to the right side of the position space is observed with increase in ⟨x⟩. This transport is seen in the quantum regime established by non-zero entanglement between the quantum walking particle and the position space.
PubDate: 2017-07-04T11:21:03.618659-05:
DOI: 10.1002/andp.201600346
- Authors: Sagnik Chakraborty; Arpan Das, Arindam Mallick, C. M. Chandrashekar
- L10 Stacked Binaries as Candidates for Hard-Magnets: FePt, MnAl and MnGa
- Authors: Yu-ichiro Matsushita; Galia Madjarova, José A. Flores-Livas, J. K. Dewhurst, C. Felser, S. Sharma, E. K. U. Gross
Abstract: We present a novel approach for designing new hard magnets by forming stacks of existing binary magnets to enhance the magneto crystalline anisotropy. This is followed by an attempt at reducing the amount of expensive metal in these stacks by replacing it with cheaper metal with similar ionic radius. This strategy is explored using examples of FePt, MnAl and MnGa. In this study a few promising materials are suggested as good candidates for hard magnets: stacked binary FePt2MnGa2 in structure where each magnetic layer is separated by two non-magnetic layers, FePtMnGa and FePtMnAl in hexagonally distorted Heusler structures and FePt0.5Ti0.5MnAl.The authors present a novel approach for designing hard magnets including no rare-earth and less expensive elements, based on the computational quantum mechanics. They formed stacks from different binaries, i.e., L10-FePt, MnGa, and MnAl, and search for optimal composition making new structures potentially interesting candidates for permanent magnets. The authors also studied stoichiometrically identical arrangements as quaternary (un)distorted Heusler structures.
PubDate: 2017-07-04T02:25:55.00945-05:0
DOI: 10.1002/andp.201600412
- Authors: Yu-ichiro Matsushita; Galia Madjarova, José A. Flores-Livas, J. K. Dewhurst, C. Felser, S. Sharma, E. K. U. Gross
- Understanding the Reaction Kinetics to Optimize Graphene Growth on Cu by
Chemical Vapor Deposition- Authors: Jürgen Kraus; Lena Böbel, Gregor Zwaschka, Sebastian Günther
Abstract: Understanding and controlling the growth kinetics of graphene is a prerequisite to synthesize this highly wanted material by chemical vapor deposition on Cu, e.g. for the construction of ultra-stable electron transparent membranes. It is reviewed that Cu foils contain a considerable amount of carbon in the bulk which significantly exceeds the expected amount of thermally equilibrated dissolved carbon in Cu and that this carbon must be removed before any high quality graphene may be grown. Starting with such conditioned Cu foils, systematic studies of the graphene growth kinetics in a reactive CH4/H2 atmosphere allow to extract the following meaningful data: prediction of the equilibrium constant of the graphene formation reaction within a precision of a factor of two, the confirmation that the graphene growth proceeds from a C(ad)-phase on Cu which is in thermal equilibrium with the reactive gas phase, its apparent activation barrier and finally the prediction of the achievable growth velocity of the growing graphene flakes during chemical vapor deposition. As a result of the performed study, growth parameters are identified for the synthesis of high quality monolayer graphene with single crystalline domains of 100–1000 μm in diameter within a reasonable growth time.A systematic study of the graphene growth on carbon depleted Cu foils allows to understand the chemical vapor deposition kinetics and to predict the achievable growth velocity of graphene flakes. The experimentally determined thermal equilibrium constant of the reaction agrees with an approximation by thermodynamic data within a factor of two. The identified optimum of the growth parameters allows the growth of high quality graphene.
PubDate: 2017-07-03T08:10:16.960401-05:
DOI: 10.1002/andp.201700029
- Authors: Jürgen Kraus; Lena Böbel, Gregor Zwaschka, Sebastian Günther
- Dimensional Confinement in Carbon-based Structures – From 3D to 1D
- Authors: Nils Richter; Zongping Chen, Marie-Luise Braatz, Fabienne Musseau, Nils-Eike Weber, Akimitsu Narita, Klaus Müllen, Mathias Kläui
Abstract: We present an overview of charge transport in selected one-, two- and three-dimensional carbon-based materials with exciting properties. The systems are atomically defined bottom-up synthesized graphene nanoribbons, doped graphene and turbostratic graphene micro-disks, where up to 100 graphene layers are rotationally stacked. For turbostratic graphene we show how this system lends itself to spintronic applications. This follows from the inner graphene layers where charge carriers are protected and thus highly mobile. Doped graphene and graphene nanoribbons offer the possibility to tailor the electronic properties of graphene either by introducing heteroatoms or by confining the system geometrically. Herein, we describe the most recent developments of charge transports in these carbon systems.This review describes the properties of carbon allotropes from 1D graphene nanoribbons to 2D doped graphene and 3D turbostratic graphene micro-disks. While turbostratic graphene lends itself to spintronic applications resulting from protected graphene layers, where charge carriers are highly mobile, doped graphene and graphene nanoribbons offer the possibility to tailor the electronic properties by introducing heteroatoms and using geometrical confinement.
PubDate: 2017-07-03T08:09:39.470098-05:
DOI: 10.1002/andp.201700051
- Authors: Nils Richter; Zongping Chen, Marie-Luise Braatz, Fabienne Musseau, Nils-Eike Weber, Akimitsu Narita, Klaus Müllen, Mathias Kläui
- Electron-Nuclear Dynamics in Molecular Harmonic Generation Driven by a
Plasmonic Nonhomogeneous Field- Authors: Li-Qiang Feng; Wen-Liang Li, Hang Liu
Abstract: Electron (z)-nuclear (R) dynamics in the molecular high-order harmonic generation (MHHG) from H2+ driven by the plasmonic nonhomogeneous field, generated by the surface plasmon polaritons in the bowtie-shaped nanostructure, have been theoretically investigated through solving the two dimensional time-dependent Schrödinger equation with the Non-Bohn-Oppenheimer approximation. It is found that (i) due to the plasmonic enhancement of the laser intensity, the harmonic cutoff can be extended when the spatial position of H2+ is away from the gap center of the nanostructure. However, due to the limit of the gap size, the threshold value of the harmonic cutoff can be obtained at a given position of H2+. (ii) Due to the asymmetric enhancement of the laser intensity in space, the extended higher harmonics are respectively from E(t)> 0 a.u. or E(t) < 0 a.u. for the cases of the positive and the negative spatial position of H2+. As a result, the intensities of the extended higher harmonics are different and can be controlled by changing the carrier-envelope phase and the pulse duration of the laser field. (iii) In the few-cycle pulse duration, the MHHG mainly comes from the multi-photon resonance ionization (MPRI), while as the pulse duration increases, the MPRI, the charge-resonance enhanced ionization (CREI) and even the dissociative ionization (DI) are contributed to the MHHG. Moreover, as the spatial position of H2+ moves, the contributions of the MHHG from the MPRI, the CERI and the DI can be controlled. (iv) The contributions of the MHHG from the two-H nuclei have been investigated and found that when E(t)> 0 a.u., the intensities of the harmonics from the negative-H is higher than those from the positive-H; while when E(t) < 0 a.u., the intensities of the harmonics from the positive-H plays the main role in the MHHG. Moreover, the multi-minima, caused by the two-center interference can also be found. (v) Finally, by superposing a properly selected harmonics, a single isolated attosecond pulse (SIAP) with the full width at half maximum (FWHM) of 34 as can be obtained.Effect of the electron-nuclear dynamics on the molecular high-order harmonic generation in the presence of the bowtie-shaped nanostructure.
PubDate: 2017-07-03T08:08:41.180972-05:
DOI: 10.1002/andp.201700093
- Authors: Li-Qiang Feng; Wen-Liang Li, Hang Liu
- Research of the Mode Instability Threshold in High Power Double Cladding
Yb-doped Fiber Amplifiers- Authors: Yanshan Wang; Qinyong Liu, Yi Ma, Yinhong Sun, Wanjing Peng, Weiwei Ke, Xiaojun Wang, Chun Tang
Abstract: We experimentally investigate the behavior of the mode instability (MI) threshold in the double cladding Yb-doped fiber amplifier when the amplifier is pumped by broad linewidth laser diodes and narrow linewidth laser diodes respectively. It is found that the MI threshold increases by 26% when the amplifier is pumped by the broad linewidth laser diodes. Experiment results show that the MI threshold is affected by the local heat load rather than the average or the total heat load. The calculation shows that the local heat deposit actually plays the key role to stimulate the MI behaviour. At the MI threshold position in the fiber, the local heat deposit also changes dramatically. The effect of the thermal conductivity on the MI threshold is also studied. Our investigation shows that the MI threshold increases from 1269 W to 1950 W when the thermal conductivity of the fiber amplifier is increased from 0.3 W/(m·K) to 5 W/(m·K). Through optimizing the pump linewidth and the cooling efficiency of the gain fiber, the MI threshold is doubled in our experiment.The double cladding Yb-doped fiber amplifier experiment shows a mode instability (MI) behavior which depends on the pump linewidth. The amplifier with different linewidth laser diodes pumping and different cooling efficiency of gain fiber, also an evaluation method of MI threshold was proposed in this paper. Both experiments and theoretical calculations reveal the local property of the MI behavior.
PubDate: 2017-07-03T01:56:37.712189-05:
DOI: 10.1002/andp.201600398
- Authors: Yanshan Wang; Qinyong Liu, Yi Ma, Yinhong Sun, Wanjing Peng, Weiwei Ke, Xiaojun Wang, Chun Tang
- Realization of Absolute-Phase Unwrapping and Speckle Suppression in Laser
Digital Holography- Authors: Mingqing Wang; Fang Li, Ming Zheng, Wei Lu, Yan Jia, Qingnan Yu, Sufen Zhao, Jian Wu
Abstract: In this paper, an absolute-phase unwrapping and speckle suppression approach to reconstruct a three-dimensional (3-D) image of an object with laser digital holography is described. This method offers three advantages to enhance the performance of the phase reconstruction technique. First, both speckle suppression and phase unwrapping are processed in the complex amplitude domain rather than in the single phase or amplitude domain. With this approach, the phase details of the object are better preserved upon phase reconstruction. Second, the proposed algorithm requires no threshold determination and thus achieves self-adaptive speckle suppression and robust phase unwrapping, in contrast to other methods. Finally, an improved dual-domain image denoising method is applied to further remove speckle-remnant-induced phase distortion. Ideal 3-D phase reconstruction results are obtained both theoretically and experimentally for the first time.The influence of speckle noise in digital holography that uses laser as the light source is problematic because it leads to unwrapped phase distortion in the 3-D phase reconstruction of the object. Thus, an absolute-phase unwrapping and speckle suppression method, which processes both speckle suppression and phase unwrapping in the complex amplitude domain, is proposed and developed herein. This method effectively removes the speckle-induced phase distortion and achieves an ideal phase reconstruction for the first time, both theoretically and experimentally.
PubDate: 2017-07-03T01:50:49.110005-05:
DOI: 10.1002/andp.201600378
- Authors: Mingqing Wang; Fang Li, Ming Zheng, Wei Lu, Yan Jia, Qingnan Yu, Sufen Zhao, Jian Wu
- Longitudinal Optical Fields in Light Scattering from Dielectric Spheres
and Anderson Localization of Light- Authors: Jose M. Escalante; Sergey E. Skipetrov
Abstract: Recent research has shown that coupling between point scatterers in a disordered medium by longitudinal electromagnetic fields is harmful for Anderson localization of light. However, it has been unclear if this feature is generic or specific for point scatterers. The present work demonstrates that the intensity of longitudinal field outside a spherical dielectric scatterer illuminated by monochromatic light exhibits a complicated, nonmonotonous dependence on the scatterer size. Moreover, the intensity is reduced for a hollow sphere, whereas one can adjust the parameters of a coated sphere to obtain a relatively low longitudinal field together with a strong resonant scattering efficiency. Therefore, random arrangements of structured (hollow or coated) spheres may be promising three-dimensional disordered materials for reaching Anderson localization of light.Longitudinal electromagnetic fields can be harmful for Anderson localization of light in ensembles of identical scatterers. This work shows that the longitudinal field outside a spherical scatterer can be minimized by tuning its internal structure (e.g., by adjusting the core and coat radii of a coated sphere). Structured scatterers may provide a solution to the longstanding problem of Anderson localization of light in three-dimensional random media.
PubDate: 2017-06-30T03:26:22.964636-05:
DOI: 10.1002/andp.201700039
- Authors: Jose M. Escalante; Sergey E. Skipetrov
- Quantum Transport in Presence of Bound States – Noise Power
- Authors: Mihail Mintchev; Luca Santoni, Paul Sorba
Abstract: The impact of bound states in Landauer-Büttiker scattering approach to non-equilibrium quantum transport is investigated. We show that the noise power at frequency ν is sensitive to all bound states with energies ωb satisfying ωb
PubDate: 2017-06-30T03:25:48.177322-05:
DOI: 10.1002/andp.201600274
- Authors: Mihail Mintchev; Luca Santoni, Paul Sorba
- Quantum Emulation of Extreme Non-Equilibrium Phenomena with Trapped Atoms
- Authors: Shankari V. Rajagopal; Kurt M. Fujiwara, Ruwan Senaratne, Kevin Singh, Zachary A. Geiger, David M. Weld
Abstract: Ultracold atomic physics experiments offer a nearly ideal context for the investigation of quantum systems far from equilibrium. We describe three related emerging directions of research into extreme non-equilibrium phenomena in atom traps: quantum emulation of ultrafast atom-light interactions, coherent phasonic spectroscopy in tunable quasicrystals, and realization of Floquet matter in strongly-driven lattice systems. We show that all three should enable quantum emulation in parameter regimes inaccessible in solid-state experiments, facilitating a complementary approach to open problems in non-equilibrium condensed matter.Extreme non-equilibrium phenomena that can be realized in atom traps include quantum emulation of ultrafast atom-light interactions, coherent phasonic spectroscopy in tunable quasicrystals, and realization of Floquet matter in strongly-driven lattice systems. All three should enable quantum emulation in parameter regimes inaccessible in solid-state experiments, facilitating a complementary approach to open problems in non-equilibrium condensed matter.
PubDate: 2017-06-30T02:56:46.875588-05:
DOI: 10.1002/andp.201700008
- Authors: Shankari V. Rajagopal; Kurt M. Fujiwara, Ruwan Senaratne, Kevin Singh, Zachary A. Geiger, David M. Weld
- Spatial Filters on Demand Based on Aperiodic Photonic Crystals
- Authors: Darius Gailevičius; Vytautas Purlys, Martynas Peckus, Roaldas Gadonas, Kestutis Staliunas
Abstract: Photonic Crystal spatial filters, apart from stand-alone spatial filtering function, can also suppress multi-transverse-mode operation in laser resonators. Here it is shown that such photonic crystals can be designed by solving the inverse problem: for a given spatial filtering profile. Optimized Photonic Crystal filters were fabricated in photosensitive glass. Experiments have shown that such filters provide a more pronounced filtering effect for total and partial transmissivity conditions.Photonic Crystal Spatial Filters, apart from stand-alone spatial filtering function, can also suppress multi-transverse-mode operation in laser resonators, increasing their beam spatial quality and its brightness. Here it is shown that such Photonic Crystals can be designed by solving the inverse problem: for a given spatial filtering profile, the architecture of the Photonic Filter can be systematically designed by a local search algorithm. Optimized Photonic Crystal Filters were fabricated in photosensitive glass. Experiments have shown that such Filters provide a more pronounced filtering effect for total and partial transmissivity conditions.
PubDate: 2017-06-30T02:10:45.127656-05:
DOI: 10.1002/andp.201700165
- Authors: Darius Gailevičius; Vytautas Purlys, Martynas Peckus, Roaldas Gadonas, Kestutis Staliunas
- Anomalous Minimum and Scaling Behavior of Localization Length Near an
Isolated Flat Band- Authors: L. Ge
Abstract: Using one-dimensional tight-binding lattices and an analytical expression based on the Green's matrix, we show that anomalous minimum of the localization length near an isolated flat band, previously found for evanescent waves in a defect-free photonic crystal waveguide, is a generic feature and exists in the Anderson regime as well, i.e., in the presence of disorder. Our finding reveals a scaling behavior of the localization length in terms of the disorder strength, as well as a summation rule of the inverse localization length in terms of the density of states in different bands. Most interestingly, the latter indicates the possibility of having two localization minima inside a band gap, if this band gap is formed by two flat bands such as in a double-sided Lieb lattice.Localization of waves occurs when a system does not support wave propagation (e.g., inside a band gap of a crystal) or due to modified wave interference introduced by disorder. How strong the localization is depends on the energy of the wave, and typically one finds the strongest localization near the middle of a band gap. This conventional wisdom is now challenged when one or more isolated flat bands are present.
PubDate: 2017-06-29T01:16:54.558958-05:
DOI: 10.1002/andp.201600182
- Authors: L. Ge
- Transport of Nonautonomous Solitons in Two-Dimensional Disordered Media
- Authors: Zhi-Yuan Sun; Xin Yu
Abstract: Transport of localized nonlinear excitations in disordered media is an interesting and important topic in modern physics. Investigated in this work is transport of two-dimensional (2D) solitons for a nonlinear Schrödinger equation with inhomogeneous nonlocality and disorder. We use the variational method to show that, the shape (size) of solitons can be manipulated through adjusting the nonlocality, which, in turn, affects the soliton mobility. Direct numerical simulations reveal that the influence of disorder on the soliton transport accords with our analysis by the variational method. Besides, we have demonstrated an anisotropic transport of the 2D nonautonomous solitons as well. Our study is expected to shed light on modulating solitons through material properties for specifying their transport in disordered media.The shape (size) of two-dimensional solitons is closely related to their mobility in disordered media. A time-dependent soliton compression and soliton expansion are realized in weak randomness, and the variance of soliton displacements is found to be affected and specified by varying the soliton shape. An elliptic-shaped soliton is also demonstrated to undergo an anisotropic transport due to its shape configuration.
PubDate: 2017-06-28T04:01:16.644224-05:
DOI: 10.1002/andp.201600323
- Authors: Zhi-Yuan Sun; Xin Yu
- Symmetry Breaking Induced Geometric Surfaces with Topological Curves in
Quantum and Classical Dynamics of the SU(2) Coupled Oscillators- Authors: Y. F. Chen; J. C. Tung, P. H. Tuan, K. F. Huang
Abstract: In the three-dimensional (3D) transversely symmetric oscillator, there are plentiful degeneracies and gaps in the quantum energy spectrum as a function of the ratio of the transverse to longitudinal frequency. It is theoretically verified that while the SU(2) interaction destroys the original degeneracies, numerous new degeneracies and gaps emerge around the original degeneracies to form a similar fine energy spectrum. The classical trajectories at the emergent degeneracies are analyzed to be localized on the 3D parametric surfaces which are constituted by the topologically invariant curves in the transverse tomography. The quantum coherent states are exploited to develop the wave functions that correspond to the 3D geometric surfaces in classical dynamics. Furthermore, the wave structures of the stationary coherent states at small quantum numbers are explored and found to display peculiar patterns with symmetries related to classical trajectories.It is theoretically verified that while the SU(2) interaction destroys the original degeneracies in the three-dimensional (3D) transversely symmetric oscillator, numerous new degeneracies and gaps emerge around the original degeneracies to form a fine energy spectrum. The classical trajectories at the emergent degeneracies are localized on the 3D parametric surfaces which are constituted by the topologically invariant curves in the transverse tomography. The quantum coherent states are developed to obtain the wave functions for manifesting the correspondence with the 3D geometric surfaces in classical dynamics. The feature of the theoretical coherent states can be linked to the formation of the experimental 3D structured laser modes.
PubDate: 2017-06-26T01:08:16.498495-05:
DOI: 10.1002/andp.201600253
- Authors: Y. F. Chen; J. C. Tung, P. H. Tuan, K. F. Huang
- Nonlinear Electrodynamics and Magnetic Black Holes
- Authors: S. I. Kruglov
Abstract: A model of nonlinear electrodynamics with two parameters, coupled with general relativity, is investigated. We study the magnetized black hole and obtain solutions. The asymptotic of the metric and mass functions at r∞ and r0, and corrections to the Reissner-Nordström solution are found. We investigate thermodynamics of black holes and calculate the Hawking temperature and heat capacity of black holes. It is shown that there are phase transitions and at some parameters of the model black holes are stable.A model of nonlinear electrodynamics with two parameters, coupled with general relativity, is investigated. The authors study the magnetized black hole and obtain solutions. The asymptotic of the metric and mass functions at r∞ and r0, and corrections to the Reissner-Nordström solution are found. The authors investigate thermodynamics of black holes and calculate the Hawking temperature and heat capacity of black holes. It is shown that there are phase transitions and at some parameters of the model black holes are stable.
PubDate: 2017-06-23T07:27:29.310557-05:
DOI: 10.1002/andp.201700073
- Authors: S. I. Kruglov
- The ergodic side of the many-body localization transition
- Authors: David J. Luitz; Yevgeny Bar Lev
Abstract: Recent studies point towards nontriviality of the ergodic phase in systems exhibiting many-body localization (MBL), which shows subexponential relaxation of local observables, subdiffusive transport and sublinear spreading of the entanglement entropy. Here we review the dynamical properties of this phase and the available numerically exact and approximate methods for its study. We discuss in which sense this phase could be considered ergodic and present possible phenomenological explanations of its dynamical properties. We close by analyzing to which extent the proposed explanations were verified by numerical studies and present the open questions in this field.The authors discuss the question of ergodicity and thermalization in disordered, interacting and isolated quantum systems, exhibiting many body localization at strong disorder. For weak disorder, such systems are ergodic and thermalize, however display anomalous static and dynamical properties. In this review the authors survey the literature and the available numerical techniques to study the ergodic phase preceding many body localization and elaborate on the notion of ergodicity in isolated quantum systems.
PubDate: 2017-05-15T01:20:57.016343-05:
DOI: 10.1002/andp.201600350
- Authors: David J. Luitz; Yevgeny Bar Lev
- Local integrals of motion in many-body localized systems
- Authors: John Z. Imbrie; Valentina Ros, Antonello Scardicchio
Abstract: We review the current (as of Fall 2016) status of the studies on the emergent integrability in many-body localized models. We start by explaining how the phenomenology of fully many-body localized systems can be recovered if one assumes the existence of a complete set of (quasi)local operators which commute with the Hamiltonian (local integrals of motions, or LIOMs). We describe the evolution of this idea from the initial conjecture, to the perturbative constructions, to the mathematical proof given for a disordered spin chain. We discuss the proposed numerical algorithms for the construction of LIOMs and the status of the debate on the existence and nature of such operators in systems with a many-body mobility edge, and in dimensions larger than one.Many-body localized systems may be considered as a peculiar class of integrable systems, characterized by extensively many conserved operators, whose quasi-local structure is responsible for the suppression of transport and thermalization. We present a review of the theoretical results concerning this emergent integrability in interacting, quantum disordered systems exhibiting localization.
PubDate: 2017-05-11T01:56:10.16395-05:0
DOI: 10.1002/andp.201600278
- Authors: John Z. Imbrie; Valentina Ros, Antonello Scardicchio
- Many-body localization in incommensurate models with a mobility edge
- Authors: Dong-Ling Deng; Sriram Ganeshan, Xiaopeng Li, Ranjan Modak, Subroto Mukerjee, J. H. Pixley
Abstract: We review the physics of many-body localization in models with incommensurate potentials. In particular, we consider one-dimensional quasiperiodic models with single-particle mobility edges. A conventional perspective suggests that delocalized states act as a thermalizing bath for the localized states in the presence of of interactions. However, contrary to this intuition there is evidence that such systems can display non-ergodicity. This is in part due to the fact that the delocalized states do not have any kind of protection due to symmetry or topology and are thus susceptible to localization. A study of such incommensurate models, in the non-interacting limit, shows that they admit extended, partially extended, and fully localized many-body states. Non-interacting incommensurate models cannot thermalize dynamically and remain localized upon the introduction of interactions. In particular, for a certain range of energy, the system can host a non-ergodic extended (i.e. metallic) phase in which the energy eigenstates violate the eigenstate thermalization hypothesis (ETH) but the entanglement entropy obeys volume-law scaling. The level statistics and entanglement growth also indicate the lack of ergodicity in these models. The phenomenon of localization and non-ergodicity in a system with interactions despite the presence of single-particle delocalized states is closely related to the so-called “many-body proximity effect” and can also be observed in models with disorder coupled to systems with delocalized degrees of freedom. Many-body localization in systems with incommensurate potentials (without single-particle mobility edges) have been realized experimentally, and we show how this can be modified to study the the effects of such mobility edges. Demonstrating the failure of thermalization in the presence of a single-particle mobility edge in the thermodynamic limit would indicate a more robust violation of the ETH.Delocalized states conventionally act as reservoirs for localized ones in systems with interactions. However, this may not be true for models with incommensurate potentials with single particle mobility edges. Such systems can host a non-ergodic extended phase in which the many-body eigenstates are not thermal but have extensive entropy. The failure of thermalization in these systems may provide a stronger violation of the eigenstate thermalization hypothesis than in conventional many-body localization.
PubDate: 2017-05-02T10:42:23.687103-05:
DOI: 10.1002/andp.201600399
- Authors: Dong-Ling Deng; Sriram Ganeshan, Xiaopeng Li, Ranjan Modak, Subroto Mukerjee, J. H. Pixley
- Signature of non-ergodicity in low-lying excitations of disordered
many-particle systems- Authors: Richard Berkovits
Abstract: Statistical properties of the low-lying states of the entanglement spectrum of a one-dimensional interacting disordered system are studied in order to understand the localized to extended transition as function of interaction strength and excitation number expected from the many-body localization transition. It is shown that such a transition is observed in the statistics of the level-spacing of the entanglement spectrum. For an intermediate range of excitation numbers and strong interaction strength where the entanglement spectrum shows a clear extended behavior, a signature of non-ergodic behavior also emerges. We interpret this as evidence for a non-ergodic-extended phase suggested by previous studies.The excitation statistics of low-lying levels of the entanglement spectrum is studied searching for a localized to extended transition as function of interaction and excitation number expected from the MBL transition. For a 1D disordered system we show that such a transition is observed. An intermediate range of excitation numbers and interaction strength appears where extended states coexist with non-ergodic behavior. This is interpreted as evidence for a non-ergodic-extended phase.
PubDate: 2017-04-27T18:56:14.138277-05:
DOI: 10.1002/andp.201700042
- Authors: Richard Berkovits
- Spectral diffusion and scaling of many-body delocalization transitions
- Authors: I. V. Gornyi; A. D. Mirlin, D. G. Polyakov, A. L. Burin
Abstract: We analyze the role of spectral diffusion in the problem of many-body delocalization in quantum dots and in extended systems. The spectral diffusion parametrically enhances delocalization, modifying the scaling of the delocalization threshold with the interaction coupling constant.This paper analyzes the role of spectral diffusion in the problem of many-body delocalization in quantum dots and in extended systems. It is shown that the spectral diffusion parametrically enhances delocalization, modifying the scaling of the delocalization threshold with the interaction coupling constant.
PubDate: 2017-04-27T18:55:15.13043-05:0
DOI: 10.1002/andp.201600360
- Authors: I. V. Gornyi; A. D. Mirlin, D. G. Polyakov, A. L. Burin
- Localization due to interaction-enhanced disorder in bosonic systems
- Authors: Rajeev Singh; Efrat Shimshoni
Abstract: Localization in interacting systems caused by disorder, known as many-body localization (MBL), has attracted a lot of attention in recent years. Most systems studied in this context also show single-particle localization, and the question of MBL is whether the phenomena survives the effects of interactions. It is intriguing to consider a system with no single-particle localization but which does localize in the presence of many particles. The localization phenomena occurs “due to” rather than “in spite of” interactions in such systems. We consider a simple bosonic system and show that interactions enhance the effects of very weak disorder and result in localization when many particles are present. We provide physical insights into the mechanism involved and support our results with analytical and numerical calculations.The phenomena of localization caused by strong disorder plays a very fundamental role in understanding the breakdown of thermalization in quantum systems. In this work it has been shown that for bosonic systems, interactions can enhance seemingly small disorder resulting in suppression of quantum fluctuations and emergence of localization. Analytical calculations highlight the role of finite disorder however small, as well as the onset of quantum behavior.
PubDate: 2017-04-13T10:44:15.573096-05:
DOI: 10.1002/andp.201600309
- Authors: Rajeev Singh; Efrat Shimshoni
- Density correlations and transport in models of many-body localization
- Authors: P. Prelovšek; M. Mierzejewski, O. Barišić, J. Herbrych
Abstract: We present a review of recent theoretical results concerning the many-body localization (MBL) phenomenon, with the emphasis on dynamical density correlations and transport quantities. They are shown to be closely related, providing a comprehensive description of the ergodic-to-nonergodic transition, consistent with experimental findings. While the focus is set mostly on the one-dimensional model of interacting spinless fermions, we also present evidence for the absence of full MBL in the one-dimensional Hubbard model and for the density-wave decay induced by the inter-chain coupling.We present a review of recent theoretical results concerning the many-body localization phenomenon, with the emphasis on dynamical density correlations and transport quantities. The focus is on the results for the one-dimensional model of interacting spinless fermions, we also present evidence for the absence of full localization in the one-dimensional Hubbard model and for the density-wave decay induced by the inter-chain coupling.
PubDate: 2017-04-11T06:20:56.248563-05:
DOI: 10.1002/andp.201600362
- Authors: P. Prelovšek; M. Mierzejewski, O. Barišić, J. Herbrych
- Density-matrix renormalization group study of many-body localization in
floquet eigenstates- Authors: Carolyn Zhang; Frank Pollmann, S. L. Sondhi, Roderich Moessner
Abstract: We generalize the recently introduced Density-Matrix Renormalization Group (DMRG-X) [Khemani et al, PRL 2016] algorithm to obtain Floquet eigenstates of one-dimensional, periodically driven many-body localized systems. This generalization is made possible by the fact that the time-evolution operator for a period can be efficiently represented using a matrix-product operator. We first benchmark the method by comparing to exact diagonalization for small systems. We then obtain Floquet eigenstates for larger systems and show unambiguously that the characteristic area-law scaling remains robust.Time-evolving block decimation and a modified density-matrix renormalization group [Khemani et al, PRL 2016] is applied to efficiently obtain Floquet eigenstates of one-dimensional, periodically driven many-body localized systems. Signatures of many-body localization such as area-law entanglement entropy remain robust over a range of parameters. A log- arithmic growth of the disorder averaged maximum entanglement entropy indicates the presence of resonant regions.
PubDate: 2017-03-31T07:10:40.991586-05:
DOI: 10.1002/andp.201600294
- Authors: Carolyn Zhang; Frank Pollmann, S. L. Sondhi, Roderich Moessner
- Sustainability of environment-assisted energy transfer in quantum
photobiological complexes- Authors: Konstantin G. Zloshchastiev
Abstract: It is shown that quantum sustainability is a universal phenomenon which emerges during environment-assisted electronic excitation energy transfer (EET) in photobiological complexes (PBCs), such as photosynthetic reaction centers and centers of melanogenesis. We demonstrate that quantum photobiological systems must be sustainable for them to simultaneously endure continuous energy transfer and keep their internal structure from destruction or critical instability. These quantum effects occur due to the interaction of PBCs with their environment which can be described by means of the reduced density operator and effective non-Hermitian Hamiltonian (NH). Sustainable NH models of EET predict the coherence beats, followed by the decrease of coherence down to a small, yet non-zero value. This indicates that in sustainable PBCs, quantum effects survive on a much larger time scale than the energy relaxation of an exciton. We show that sustainable evolution significantly lowers the entropy of PBCs and improves the speed and capacity of EET.The work addresses a long-standing problem of quantum photobiology and UV-physiology: is there a universal mechanism, which would explain high efficiency and sustainability of energy transfer in otherwise completely different photobiological systems inside living organisms or organelles, such as photosynthetic reaction centers and centers of melanogenesis? It is shown that certain interactions of these systems with their environment facilitate energy transfer, preserve quantum coherence and reduce entropy.
PubDate: 2017-03-30T06:20:46.923457-05:
DOI: 10.1002/andp.201600185
- Authors: Konstantin G. Zloshchastiev
- Localization lifetime of a many-body system with periodic constructed
disorder- Authors: Michael Schecter; Michael Shapiro, Mark I. Dykman
Abstract: We show that, in a many-body system, all particles can be strongly confined to the initially occupied sites for a time that scales as a high power of the ratio of the bandwidth of site energies to the hopping amplitude. Such time-domain formulation is complementary to the formulation of the many-body localization of all stationary states with a large localization length. The long localization lifetime is achieved by constructing a periodic sequence of site energies with a large period in a one-dimensional chain. The scaling of the localization lifetime is independent of the number of particles for a broad range of the coupling strength. The analytical results are confirmed by numerical calculations.How long can strongly interacting particles stay almost entirely confined to the sites they initially occupied? Unexpectedly, a long confinement time can be achieved for a periodic sequence of site energies. A “magic” period is 6. For such a period, judiciously constructed site energies lead to the confinement for times that scale as (h/J)5 in a broad range of the particle-particle interaction V.
PubDate: 2017-03-27T13:15:39.864567-05:
DOI: 10.1002/andp.201600366
- Authors: Michael Schecter; Michael Shapiro, Mark I. Dykman
- Many-body localization from the perspective of Integrals of Motion
- Authors: Louk Rademaker; Miguel Ortuño, Andres M. Somoza
Abstract: We study many-body localization (MBL) from the perspective of integrals of motion (IOMs). MBL can be understood phenomenologically through the existence of macroscopically many localized IOMs. We develop a systematic procedure based on IOM to calculate many-body quantities. Displacement transformations made clear that any operator can be expanded in 1-,2- ... n-particles terms. We use this property to develop a systematic procedure to approximately calculate IOMs and many-body quantities. We characterize the decay with distance of the IOM's and their interactions through effective localization lengths. For all values of disorder the typical IOMs are localized, suggesting the importance of rare fluctuations in understanding the MBL-to-ergodic transition.Many-body localization can be understood through the existence of macroscopically many localized integrals of motion. We develop a systematic procedure to calculate integrals of motion and many-body quantities. We characterize their decay with distance and their interactions through effective localization lengths. An analysis of the coefficients of the integrals of motion suggests the importance of rare fluctuations in understanding the many-body localization problem.
PubDate: 2017-03-27T01:45:43.952322-05:
DOI: 10.1002/andp.201600322
- Authors: Louk Rademaker; Miguel Ortuño, Andres M. Somoza
- Localization properties of the disordered XY spin chain
- Authors: Houssam Abdul-Rahman; Bruno Nachtergaele, Robert Sims, Günter Stolz
Abstract: We review several aspects of Many-Body Localization-like properties exhibited by the disordered XY chains: localization properties of the energy eigenstates and thermal states, propagation bounds of Lieb-Robinson type, decay of correlation functions, absence of particle transport, bounds on the bipartite entanglement, and bounded entanglement growth under the dynamics. We also prove new results on the absence of energy transport and Fock space localization. All these properties are made accessible to mathematical analysis due to the exact mapping of the XY chain to a system of quasi-free fermions given by the Jordan-Wigner transformation. Motivated by these results we discuss conjectured properties of more general disordered quantum spin and other systems as possible directions for future mathematical research.Zero-velocity Lieb-Robinson bounds, describing the absence of information transport, are arising as one of the characteristics of the many-body localized phase in disordered quantum spin systems. These bounds and other many-body localization properties, including exponential clustering and area laws for the bipartite entanglement of eigenstates at arbitrary energy, can be proven rigorously for the disordered XY chain.
PubDate: 2017-03-24T03:10:58.280078-05:
DOI: 10.1002/andp.201600280
- Authors: Houssam Abdul-Rahman; Bruno Nachtergaele, Robert Sims, Günter Stolz
- Dynamical many-body localization and delocalization in periodically driven
closed quantum systems- Authors: Asmi Haldar; Arnab Das
Abstract: Quantum interference lies at the heart of several surprising equilibrium and non-equilibrium phenomena in many-body Physics. Here we discuss two recently explored non-equilibrium scenarios where external periodic drive applied to closed (i.e., not attached to any external bath) quantum many-body systems have apparently opposite effects in respective cases. In one case it freezes/localizes a disorder free system dynamically, while in the other it delocalizes a disordered many-body localized system, and quantum interference is responsible for both the effects. We review these in the perspective of more general questions of ergodicity, energy absorption, asymptotic behavior, and finally the essential role of quantum mechanics in understanding these issues in periodically driven closed many-body systems. In this article we intend to deliver a non-technical account of some recent developments in this field in a manner accessible to a broad readership.Periodic drive can induce both localization and delocalization in many-body quantum systems. Free systems can undergo Dynamical Many-body Freezing (freezing of population dynamics for all degrees of freedom) under periodic drive (upper line: freeing of transverse magnetization in a transverse field Ising chain), while an originally Many-body Localized system can be delocalized completely under periodic drive (lower line: flat Eigenstate Expectation Values vs Floquet quasienergies of an onsite occupation number).
PubDate: 2017-03-21T05:11:55.305211-05:
DOI: 10.1002/andp.201600333
- Authors: Asmi Haldar; Arnab Das
- Coherent backscattering in the Fock space of ultracold bosonic atoms
- Authors: Peter Schlagheck; Julien Dujardin
Abstract: We present numerical evidence for the occurrence of coherent backscattering in the Fock space of a small disordered Bose-Hubbard system consisting of four sites and containing five particles. This many-body interference phenomenon can most conveniently be seen in time evolution processes that start from a Fock state of the Bose-Hubbard system. It manifests itself in an enhanced detection probability of this initial state as compared to other Fock states with comparable total energy. We argue that coherent backscattering in Fock space can be experimentally measured with ultracold bosonic atoms in optical lattices using state-of-the-art single-site detection techniques. A synthetic gauge field can be induced in order to break time-reversal symmetry within the lattice and thereby destroy coherent backscattering. While this many-body interference effect is most prominently visible in the presence of eigenstate thermalization, we briefly discuss its significance in the opposite regime of many-body localization.A quantum many-body system that is prepared in a specific Fock state with respect to a single-particle basis has an enhanced probability to come back to this initial state in the course of time evolution as compared to other Fock states with comparable energy. This effect arises due to coherent backscattering in Fock space. It can be probed using ultracold bosonic atoms in optical lattices.
PubDate: 2017-03-21T05:11:21.087483-05:
DOI: 10.1002/andp.201600311
- Authors: Peter Schlagheck; Julien Dujardin
- Localization and chaos in a quantum spin glass model in random
longitudinal fields: Mapping to the localization problem in a Bethe
lattice with a correlated disorder- Authors: Alexander Burin
Abstract: The analytical solution of a many-body localization problem in a quantum Sherrington-Kirkpatrick spin glass model in a random longitudinal field is proposed matching the problem with a model of Anderson localization in a Bethe lattice. The localization transition is dramatically sensitive to the relationship between interspin interaction and random field revealing different regimes in which the interaction can either suppress or enhance the delocalization. The localization is enhanced by decreasing the temperature and the localization transition shows a remarkable universality in a spin glass phase. The observed trends should be qualitatively relevant for other systems showing many-body localization.Analytical solution is developed for many-body localization in a quantum spin glass model with an infinite range spin-spin binary interaction using a matching localization problem on a Bethe lattice that can be solved exactly. The dependencies of localization threshold on random fields, interaction and temperature are determined in this model and similar behaviors are expected in more realistic settings.
PubDate: 2017-03-21T04:50:23.889449-05:
DOI: 10.1002/andp.201600292
- Authors: Alexander Burin
- Localization-delocalization transitions in bosonic random matrix ensembles
- Authors: N. D. Chavda; V. K. B. Kota
Abstract: Localization to delocalization transitions in eigenfunctions are studied for finite interacting boson systems by employing one- plus two-body embedded Gaussian orthogonal ensemble of random matrices [EGOE(1+2)]. In the first analysis, considered are bosonic EGOE(1+2) for two-species boson systems with a fictitious (F) spin degree of freedom [called BEGOE(1+2)-F]. Numerical calculations are carried out as a function of the two-body interaction strength (λ). It is shown that, in the region (defined by λ>λc) after the onset of Poisson to GOE transition in energy levels, the strength functions exhibit Breit-Wigner to Gaussian transition for λ>λFk>λc. Further, analyzing information entropy and participation ratio, it is established that there is a region defined by λ∼λt where the system exhibits thermalization. The F-spin dependence of the transition markers λFk and λt follow from the propagator for the spectral variances. These results, well tested near the center of the spectrum and extend to the region within ±2σ to ±3σ from the center (σ2 is the spectral variance), establish universality of the transitions generated by embedded ensembles. In the second analysis, entanglement entropy is studied for spin-less BEGOE(1+2) ensemble and shown that the results generated are close to the recently reported results for a Bose-Hubbard model.Universality of the localizaton-delocalization transitions generated by embedded random interaction matrix ensembles is established by showing that the ensembles for two species boson systems with a fictitious spin-1/2 degree of freedom, generate three transition markers. The third marker defines a region of thermalization. Also for the first time, the bipartite entanglement entropy is studied using embedded ensembles for spin-less boson systems and shown that the results are close to those obtained recently using Bose-Hubbard models.
PubDate: 2017-03-09T09:05:43.170199-05:
DOI: 10.1002/andp.201600287
- Authors: N. D. Chavda; V. K. B. Kota
- Solitons in one-dimensional lattices with a flat band
- Authors: Dario Bercioux; Omjyoti Dutta, Enrique Rico
Abstract: We investigate the spectral properties of a quasi-one-dimensional lattice in two possible dimerisation configurations. Both configurations are characterised by the same lattice topology and the identical spectra containing a flat band at zero energy. We find that, one of the dimerised configuration has similar symmetry to a one-dimensional chain proposed by Su-Schrieffer-Heeger for studying solitons in conjugated polymers. Whereas, the other dimerised configuration only shows non-trivial topological properties in the presence of chiral-symmetry breaking adiabatic pumping.We study an enlarged version of the popular SSH model for studying solitons in polyacetylene. Our system allows for two possible dimerized phases. We show that one of the two is a higher dimensional representation of the SSH model, whereas the second one is a trivial representation that does not show any topological phase.
PubDate: 2017-03-08T03:15:44.38263-05:0
DOI: 10.1002/andp.201600262
- Authors: Dario Bercioux; Omjyoti Dutta, Enrique Rico
- Classical and quantum systems: transport due to rare events
- Authors: François Huveneers
Abstract: We review possible mechanisms for energy transfer based on ‘rare’ or ‘non-perturbative’ effects, in physical systems that present a many-body localized phenomenology. The main focus is on classical systems, with or without quenched disorder. For non-quantum systems, the breakdown of localization is usually not regarded as an issue, and we thus aim at identifying the fastest channels for transport. Next, we contemplate the possibility of applying the same mechanisms in quantum systems, including disorder free systems (e.g. Bose-Hubbard chain), disordered many-body localized systems with mobility edges at energies below the edge, and strongly disordered lattice systems in d>1. For quantum mechanical systems, the relevance of these considerations for transport is currently a matter of debate.In this feature article, the author reviews some recent progress in the understanding of the MBL phase. The focus is on the role of rare ergodic spots that can potentially harm the stability of the localized phase. Such spots naturally occur through local inclusions of the thermal phase in the localized phase, which are unavoidable in any realistic interacting system, due to either thermal fluctuations or disorder fluctuations.
PubDate: 2017-03-02T02:40:30.514173-05:
DOI: 10.1002/andp.201600384
- Authors: François Huveneers
- Beta-functions of non-linear σ-models for disordered and interacting
electron systems- Authors: Luca Dell'Anna
Abstract: We provide and study complete sets of one-loop renormalization group equations of several Finkel'stein non-linear σ models, the effective field theories describing the diffusive quantum fluctuations in correlated disordered systems. We consider different cases according to the presence of certain symmetries induced by the original random Hamiltonians, and we show that, for interacting systems, the Cartan's classification of symmetry classes is not enough to uniquely determine their scaling behaviors.The study of the interplay beteen disorder and interactions, which is the origin of still unclear phenomena in electron systems, is a challenging task for modern condensed matter physicists. One of the most powerful and versatile tool to deal with disordered correlated fermions is the non-linear sigma-model approach, which takes into account the symmetry properties of different random systems allowing for a systematic study in terms of symmetry classes.
PubDate: 2017-02-28T05:11:17.942242-05:
DOI: 10.1002/andp.201600317
- Authors: Luca Dell'Anna
- Elastic wave transport in disordered, isotropic media: a supersymmetric
sigma model- Authors: Douglas M. Photiadis
Abstract: Starting from a continuum description of a disordered elastic medium, we have derived a supersymmetric field theoretic model enabling the prediction of ensemble average correlation functions that fully takes polarization effects into account. The model enables both perturbative and non-perturbative calculations in a similar fashion as corresponding models of disordered electronic systems. At intermediate distances, we show that a Hubbard-Stratonovic transformation can be carried out and obtain a supermatrix field theory. At distances far greater than the mean free paths of the system, we show that the action reduces to a nonlinear supersymmetric sigma model formally identical to that for a scalar field. Our results yield a bare diffusion constant given by a density of states weighted average of the classical diffusion constants of the coherent potential approximation(CPA) medium.The transport of vibrational energy in disordered solids is important across a broad range of physical systems. While much progress has been made, a full theoretical description of such systems has yet to be given, particularly with regard to the interference phenomena leading to enhanced backscattering and localization effects. This article presents a theoretical advance enabling a fuller and more accurate description of such phenomena.
PubDate: 2017-02-27T06:50:58.467875-05:
DOI: 10.1002/andp.201600353
- Authors: Douglas M. Photiadis
- Absence of many-body localization in a continuum
- Authors: I. V. Gornyi; A. D. Mirlin, M. Müller, D. G. Polyakov
Abstract: We consider an extended electronic system with localized single-particle states coupled by short-range interactions, in the absence of coupling to an external bath. We show that many-body localization, which exists in tight-binding models, is unstable in a continuum. Irrespective of the dimensionality of the system, many-body localization does not survive the unbounded growth of the single-particle localization length with increasing energy that is characteristic of the continuum limit. The system remains delocalized down to arbitrarily small temperature T, although its dynamics slows down as T decreases. Remarkably, the conductivity vanishes with decreasing T faster than in the Arrhenius law. The system can be characterized by an effective T-dependent single-particle mobility edge which diverges in the limit of T0. Delocalization is driven by interactions between hot electrons above the mobility edge and the “bath” of thermal electrons in the vicinity of the Fermi level.It is shown that many-body localization does not survive in a continuum, since high-energy excitations form a weak delocalized bath. In dimensions d=1 and 2, instead of super-insulation one finds a regime of low-temperature transport with a resistivity that increases in a super-Arrhenius fashion. The latter is identified as a key hallmark of systems as close as possible to being many-body localized.
PubDate: 2017-02-14T08:25:36.981453-05:
DOI: 10.1002/andp.201600365
- Authors: I. V. Gornyi; A. D. Mirlin, M. Müller, D. G. Polyakov
- Models for a multimode bosonic tunneling junction
- Authors: David Fischer; Sandro Wimberger
Abstract: We discuss the relaxation dynamics for a bosonic tunneling junction with two modes in the central potential well. We use a master equation description for ultracold bosons tunneling in the presence of noise and incoherent coupling processes into the two central modes. Whilst we cannot quantitatively reproduce the experimental data of the setup reported in [Phys. Rev. Lett. 115, 050601 (2015)], we find a reasonable qualitative agreement of the refilling process of the initially depleted central site. Our results may pave the way for the control of bosonic tunneling junctions by the simultaneous presence of decoherence processes and atom-atom interaction.The relaxation dynamics are studied for a bosonic tunneling junction with two modes in the central potential well. The importance of incoherent processes in the refilling of the initially depleted central site is shown and qualitative agreement with recent experimental results is obtained.
PubDate: 2017-02-13T05:55:54.775068-05:
DOI: 10.1002/andp.201600327
- Authors: David Fischer; Sandro Wimberger
- Macroscopic and microscopic thermal equilibrium
- Authors: Sheldon Goldstein; David A. Huse, Joel L. Lebowitz, Roderich Tumulka
Abstract: We study the nature of and approach to thermal equilibrium in isolated quantum systems. An individual isolated macroscopic quantum system in a pure or mixed state is regarded as being in thermal equilibrium if all macroscopic observables assume rather sharply the values obtained from thermodynamics. Of such a system (or state) we say that it is in macroscopic thermal equilibrium (MATE). A stronger requirement than MATE is that even microscopic observables (i.e., ones referring to a small subsystem) have a probability distribution in agreement with that obtained from the micro-canonical, or equivalently the canonical, ensemble for the whole system. Of such a system we say that it is in microscopic thermal equilibrium (MITE). The distinction between MITE and MATE is particularly relevant for systems with many-body localization (MBL) for which the energy eigenfuctions fail to be in MITE while necessarily most of them, but not all, are in MATE. However, if we consider superpositions of energy eigenfunctions (i.e., typical wave functions ψ) in an energy shell, then for generic macroscopic systems, including those with MBL, most ψ are in both MATE and MITE. We explore here the properties of MATE and MITE and compare the two notions, thereby elaborating on ideas introduced in .In quantum mechanics, there are two types of thermal equilibrium, and their difference is particularly relevant to systems with many-body localization: In the first and basic type, all macroscopic observables assume rather sharply their equilbrium values. A second and stronger type, but still valid for most states, is that even microscopic observables are distributed according to their thermal equilibrium distribution.
PubDate: 2017-02-09T02:20:50.063585-05:
DOI: 10.1002/andp.201600301
- Authors: Sheldon Goldstein; David A. Huse, Joel L. Lebowitz, Roderich Tumulka
- One-particle density matrix characterization of many-body localization
- Authors: Soumya Bera; Thomas Martynec, Henning Schomerus, Fabian Heidrich-Meisner, Jens H. Bardarson
Abstract: We study interacting fermions in one dimension subject to random, uncorrelated onsite disorder, a paradigmatic model of many-body localization (MBL). This model realizes an interaction-driven quantum phase transition between an ergodic and a many-body localized phase, with the transition occurring in the many-body eigenstates. We propose a single-particle framework to characterize these phases by the eigenstates (the natural orbitals) and the eigenvalues (the occupation spectrum) of the one-particle density matrix (OPDM) in individual many-body eigenstates. As a main result, we find that the natural orbitals are localized in the MBL phase, but delocalized in the ergodic phase. This qualitative change in these single-particle states is a many-body effect, since without interactions the single-particle energy eigenstates are all localized. The occupation spectrum in the ergodic phase is thermal in agreement with the eigenstate thermalization hypothesis, while in the MBL phase the occupations preserve a discontinuity at an emergent Fermi edge. This suggests that the MBL eigenstates are weakly dressed Slater determinants, with the eigenstates of the underlying Anderson problem as reference states. We discuss the statistical properties of the natural orbitals and of the occupation spectrum in the two phases and as the transition is approached. Our results are consistent with the existing picture of emergent integrability and localized integrals of motion, or quasiparticles, in the MBL phase. We emphasize the close analogy of the MBL phase to a zero-temperature Fermi liquid: in the studied model, the MBL phase is adiabatically connected to the Anderson insulator and the occupation-spectrum discontinuity directly indicates the presence of quasiparticles localized in real space. Finally, we show that the same picture emerges for interacting fermions in the presence of an experimentally-relevant bichromatic lattice and thereby demonstrate that our findings are not limited to a specific model.In finite quantum systems, interactions and disorder often work complementary. We provide a bridge between the clearly observable effects for individual particles and the collective many-body behavior, obtained by inspecting the shape and occupation of natural single-particle orbitals. Beyond a certain disorder strength, particles in these orbitals become spatially confined and the occupations well defined. This phenomenology aligns well with the transition to a many-body-localised phase.
PubDate: 2017-02-06T01:45:53.796913-05:
DOI: 10.1002/andp.201600356
- Authors: Soumya Bera; Thomas Martynec, Henning Schomerus, Fabian Heidrich-Meisner, Jens H. Bardarson
- Eigenstate phase transitions and the emergence of universal dynamics in
highly excited states- Authors: S. A. Parameswaran; Andrew C. Potter, Romain Vasseur
Abstract: We review recent advances in understanding the universal scaling properties of non-equilibrium phase transitions in non-ergodic disordered systems. We discuss dynamical critical points (also known as eigenstate phase transitions) between different many-body localized (MBL) phases, and between MBL and thermal phases.Disordered quantum systems open the door to new dynamical phase transitions far from thermal equilibrium.
PubDate: 2017-01-20T06:25:49.234482-05:
DOI: 10.1002/andp.201600302
- Authors: S. A. Parameswaran; Andrew C. Potter, Romain Vasseur
- Extended nonergodic states in disordered many-body quantum systems
- Authors: E. J. Torres-Herrera; Lea F. Santos
Abstract: This work supports the existence of extended nonergodic states in the intermediate region between the chaotic (thermal) and the many-body localized phases. These states are identified through an extensive analysis of static and dynamical properties of a finite one-dimensional system with onsite random disorder. The long-time dynamics is particularly sensitive to changes in the spectrum and in the structures of the eigenstates. The study of the evolution of the survival probability, Shannon information entropy, and von Neumann entanglement entropy enables the distinction between the chaotic and the intermediate region.Despite the consensus that the transition from a metal to an insulator can still take place in quantum systems with many interacting particles, the details are not entirely understood. It has been debated, for instance, whether there is an intermediate phase between the chaotic and the many-body localized phase. Our results for the long-time evolution of the survival probability makes clear the existence of the intermediate region.
PubDate: 2017-01-13T14:15:40.242054-05:
DOI: 10.1002/andp.201600284
- Authors: E. J. Torres-Herrera; Lea F. Santos
- Rare-region effects and dynamics near the many-body localization
transition- Authors: Kartiek Agarwal; Ehud Altman, Eugene Demler, Sarang Gopalakrishnan, David A. Huse, Michael Knap
Abstract: The low-frequency response of systems near the many-body localization phase transition, on either side of the transition, is dominated by contributions from rare regions that are locally “in the other phase”, i.e., rare localized regions in a system that is typically thermal, or rare thermal regions in a system that is typically localized. Rare localized regions affect the properties of the thermal phase, especially in one dimension, by acting as bottlenecks for transport and the growth of entanglement, whereas rare thermal regions in the localized phase act as local “baths” and dominate the low-frequency response of the MBL phase. We review recent progress in understanding these rare-region effects, and discuss some of the open questions associated with them: in particular, whether and in what circumstances a single rare thermal region can destabilize the many-body localized phase.The many-body localization transition demarcates quantum phases of matter that are remarkably different in their entanglement structure, response, and dynamical properties. Near the transition, this difference plays a significant role as rare inclusions of the opposite phase strongly modify the properties of the bulk, ‘enabling’ the transition, but also giving rise to a new ‘Griffiths’ phase with entirely novel dynamical characteristics. This review reflects the current understanding of such ‘Griffiths’ effects on the many-body localization transition.
PubDate: 2017-01-12T13:30:54.653485-05:
DOI: 10.1002/andp.201600326
- Authors: Kartiek Agarwal; Ehud Altman, Eugene Demler, Sarang Gopalakrishnan, David A. Huse, Michael Knap