Showing papers in "EPL in 2020"

Can we study the many-body localisation transition?

Abstract: We present a detailed analysis of the length- and timescales needed to approach the critical region of MBL from the delocalised phase, studying both eigenstates and the time evolution of an initial state. For the eigenstates we show that in the delocalised region there is a single length, which is a function of disorder strength, controlling the finite-size flow. Small systems look localised, and only for larger systems do resonances develop which restore ergodicity in the form of the eigenstate thermalisation hypothesis. For the transport properties, we study the time necessary to transport a single spin across a domain wall, showing how this grows quickly with increasing disorder, and compare it with the Heisenberg time. For a sufficiently large system the Heisenberg time is always larger than the transport time, but for a smaller system this is not necessarily the case. We conclude that the properties of the MBL transition cannot be explored using the system sizes or times available to current numerical and experimental studies.

Spatio-temporal propagation of COVID-19 pandemics

Abstract: The coronavirus known as COVID-19 has spread worldwide since December 2019 Without any vaccination or medicine, the means of controlling it are limited to quarantine and social distancing Here we study the spatio-temporal propagation of the first wave of the COVID-19 virus in China and compare it to other global locations We provide a comprehensive picture of the spatial propagation from Hubei to other provinces in China in terms of distance, population size, and human mobility and their scaling relations Since strict quarantine has been usually applied between cities, more insight into the temporal evolution of the disease can be obtained by analyzing the epidemic within cities, especially the time evolution of the infection, death, and recovery rates which affected by policies We compare the infection rate in different cities in China and provinces in Italy and find that the disease spread is characterized by a two-stages process In early times, of the order of few days, the infection rate is close to a constant probably due to the lack of means to detect infected individuals before infection symptoms are observed Then at later times it decays approximately exponentially due to quarantines This exponential decay allows us to define a characteristic time of controlling the disease which we found to be approximately 20 days for most cities in China in marked contrast to different provinces in Italy which are characterized with much longer controlling time indicating less efficient controlling policies Moreover, we study the time evolution of the death and recovery rates which we found to show similar behavior as the infection rate and reflect the health system situation which could be overloaded © Copyright2020 EPLA

Thermodynamic control —An old paradigm with new applications

Abstract: Tremendous research efforts have been invested in exploring and designing so-called shortcuts to adiabaticity. These are finite-time processes that produce the same final states that would result from infinitely slow driving. Most of these techniques rely on auxiliary fields and quantum control, which makes them rather costly to implement. In this Perspective we outline an alternative paradigm for optimal control that has proven powerful in a wide variety of situations ranging from heat engines over chemical reactions to quantum dynamics —thermodynamic control. Focusing on only a few, selected milestones we seek to provide a pedagogical entry point into this powerful and versatile framework.

Full counting statistics in the gapped XXZ spin chain

Abstract: We exploit the knowledge of the entanglement spectrum in the ground state of the gapped XXZ spin chain to derive asymptotic exact results for the full counting statistics of the transverse magnetisation in a spin block of length. We found that for a subsystem of even length the full counting statistics is Gaussian, while for odd subsystems it is the sum of two Gaussian distributions. We test our analytic predictions with accurate tensor networks simulations. As a byproduct, we also obtain the symmetry (magnetisation) resolved entanglement entropies.

Non-Markovian quantum dynamics: What is it good for?

Abstract: Recent developments in practical quantum engineering and control techniques have allowed significant developments for experimental studies of open quantum systems and decoherence engineering. Indeed, it has become possible to test experimentally various theoretical, mathematical, and physical concepts related to non-Markovian quantum dynamics. This includes experimental characterization and quantification of non-Markovian memory effects and proof-of-principle demonstrations how to use them for certain quantum communication and information tasks. We describe here recent experimental advances for open system studies, focussing in particular to non-Markovian dynamics including the applications of memory effects, and discuss the possibilities for ultimate control of decoherence and open system dynamics.

Novel cosmological and black hole solutions in Einstein and higher-derivative gravity in two dimensions

Abstract: This work is partially supported by MEXT KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas “Cosmic Acceleration” No. 15H05890 (S.N.) and the JSPS Grant-in-Aid for Scientific Research (C) No. 18K03615 (S.N.), and by MINECO (Spain), FIS2016-76363-P (S.D.O).

Aspects of axion F(R) gravity

Abstract: We provide a compact review on recent developments on axion F (R ) gravity. The axion field is a string-theory–originated theoretical particle that is a perfect candidate for low-mass particle dark matter. In this review we present how a viable inflationary phenomenology and a viable late-time evolution can be described by an axion F (R ) gravity theory, in which the F (R ) gravity part can drive in a geometric way the inflationary and the late-time era, and the axion field behaves as dark matter, with its energy density behaving as a function of the scale factor as . We also briefly discuss the effect of a non-trivial axion Chern-Simons coupling on the inflationary phenomenology of the R 2 model. Finally, we briefly discuss the effects of a non-minimal coupling of the axion field with the curvature on neutron stars, and also the propagation of gravity waves in Chern-Simons axion gravity.

Self-organized criticality and earthquake predictability: A long-standing question in the light of natural time analysis

Abstract: After the Bak-Tang-Wisenfeld seminal work on self-organized criticality (SOC), the following claim appeared by other workers in the 1990s: Earthquakes (EQs) cannot be predicted, since the Earth is in a state of SOC and hence any small earthquake has some probability of cascading into a large event. Here, we discuss that such claims do not stand in the light of natural time analysis, which was shown at the beginning of the 2000s to extract the maximum information possible from complex systems time series. A useful quantity to identify the approach of a dynamical system to criticality is the variance of natural time χ , which becomes equal to 0.070 at the critical state for a variety of dynamical systems. This also holds for experimental results of critical phenomena such as growth of ricepiles, seismic electric signals activities, and the subsequent seismicity before the associated main shock. Another useful quantity is the change of the dynamic entropy under time reversal, which is minimized before a large avalanche upon analyzing the Olami-Feder-Christensen model for EQs in natural time. Such a minimum actually occurred on 22 December 2010, well before the M9 Tohoku EQ in Japan on 11 March 2011, being accompanied by increases of both the complexity measure of the fluctuations and the variability of the order parameter of seismicity (which was minimized two weeks later). These increases conform to the seminal work on phase transitions by Lifshitz and Slyozov and independently by Wagner as well as to more recent work by Penrose et al . In addition, the evolution of the complexity measure of the fluctuations reveals a reliable estimation of the occurrence time of this M9 EQ.

A nearly massless graviton in Einstein-Gauss-Bonnet inflation with linear coupling implies constant-roll for the scalar field

Abstract: The striking GW170817 event indicated that the graviton is nearly massless, since the gamma rays emitted from the two neutron stars merging arrived almost simultaneously with the gravitational waves. Thus, the graviton must also be massless during the inflationary and post-inflationary era, since there is no obvious reason to believe otherwise. In this letter we shall investigate the theoretical implications of the constraint that the graviton is massless to an Einstein-Gauss-Bonnet theory with linear coupling of the scalar field to the four dimensional Gauss-Bonnet invariant. As we show, the constraint of having gravitational wave speed of the primordial gravitational waves equal to one, severely restricts the dynamics of the scalar field, imposing a direct constant-roll evolution on it. Also, as we show, the spectral index of the primordial scalar perturbations for the GW170817-compatible Einstein-Gauss-Bonnet theory with linear coupling is different in comparison to the same theory with non-linear coupling. Thus the phenomenology of the model is expected to be different, and we briefly discuss this issue too. In addition, the constant-roll condition is always related to non-Gaussianities, thus it is interesting that the imposition of a massless graviton in an Einstein-Gauss-Bonnet theory with linear coupling may lead to non-Gaussianities, so we briefly discuss this issue too.

Aharonov-Bohm effect on a generalized Klein-Gordon oscillator with uniform magnetic field in a spinning cosmic string space-time

Abstract: In this work, we study a generalized Klein-Gordon oscillator field on the background space-time induced by spinning cosmic string coupled to a homogeneous magnetic field including a magnetic quantum flux. We solve the generalized Klein-Gordon oscillator equation in the considered system and obtain the energy eigenvalues and eignfunctions and analyze a relativistic analogue of the Aharonov-Bohm effect.

Fluctuations of the entropy change under time reversal: Further investigations on identifying the occurrence time of an impending major earthquake

Abstract: A procedure has been developed in a previous publication (Skordas E. S. et al., EPL, 128 (2019) 49001) for the identification of the occurrence time of the Tohoku earthquake of magnitude M = 9.0 that occurred in Japan on 11 March 2011 based on natural time analysis of seismicity. Using the complexity measure that quantifies the fluctuations of the entropy change ΔS of seismicity under time reversal, we show here that, in the longer scales, the complexity measure of the entire Japanese region starts increasing from 22 December 2010 (the date at which ΔS is minimized) reaching a maximum close to the appearance of a Seismic Electric Signals activity (evidenced from the recording of anomalous magnetic field variations on the z-component) in the beginning of January 2011; then it gradually diminishes until just before the mega earthquake. On the other hand, around two days before its occurrence, the complexity measure in the candidate epicentral area exhibits an abrupt increase. This difference reveals, well in advance, that the M7.3 earthquake on 9 March 2011 was a foreshock. Copyright c © EPLA, 2020 Introduction. – It is widely accepted [1–3] that earthquakes (EQs), which exhibit complex correlations in time, space and magnitude (M) (e.g., [4–11]), can be considered as critical phenomena, since the observed EQ scaling laws [12] indicate the existence of phenomena closely associated with the proximity of the system to a critical point. The order parameter of seismicity is the quantity by which one can identify the approach of the dynamical system to a critical point. The introduction of such a parameter for the case of seismicity, labeled hereafter κ1, became possible after the suggestion of a new procedure for the analysis of complex time series, termed natural time analysis, which was introduced in the beginning of the 2000s (e.g., see ref. [13]) and is summarized in the next section. The Tohoku mega earthquake of magnitude 9.0 that occurred in Japan on 11 March 2011 devastated the Pacific side of northern Honshu with a huge tsunami causing more than 20000 victims and serious damage to the Fukushima nuclear plant. It is the largest magnitude event recorded in Japan and seismologists were shocked because it was not even considered possible that it might happen in the East Japan subduction zone. This mega earthquake was preceded by a M7.3 foreshock that occurred almost two days before. Upon the occurrence of this M7.3 EQ, seismologists could not identify that this was foreshock of a significantly larger EQ, which would be of paramount importance for practical purposes. It is one of the main goals of this paper to investigate whether such an identification was possible by means of the fluctuations of the entropy change ΔS under time reversal (i.e., upon reversing the direction of the time arrow). We clarify that the concept of entropy S in natural time defined below is applicable to deterministic as well as stochastic processes. It is a dynamic entropy depending on the sequential order of events and is fundamentally different [14,15] from other entropies. The quantity ΔS is a measure that may serve for the identification of when the system approaches the critical

Pattern formations driven by cyclic interactions: A brief review of recent developments

Abstract: Lotka's seminal work (A.J. Lotka A., Proc. Natl. Acad. Sci. U.S.A. 6 (1920) 410) "on certain rhythmic relations'' is already one hundred years old, but the research activity about pattern formations due to cyclical dominance is more vibrant than ever. It is because non-transitive interactions have paramount role on maintaining biodiversity and adequate human intervention into ecological systems requires deeper understanding of related dynamical processes. In this perspective article we overview different aspects of biodiversity, with focus on how it can be maintained based on mathematical modeling of last years. We also briefly discuss the potential links to evolutionary game models of social systems, and finally, give an overview about potential prospects for future research.

A connection between Rastall-type and f(R, T) gravities

Abstract: Recently a Lagrangian formulation for Rastall Gravity (RG) has been proposed in the framework of f (R , T ) gravity. In the present work we obtain Lagrangian formulation for the standard Rastall theory assuming the matter content is a perfect fluid with linear Equation of State (EoS). We therefore find a relation between the coupling constant of the Lagrangian, the Rastall gravitational coupling constant and the EoS parameter. We also propose a Lagrangian for the Generalized Rastall Gravity (GRG). In this case the Rastall parameter which is a constant is replaced by a variable one. More exactly, it appears as a function of the Ricci scalar and the trace of the Energy Momentum Tensor (EMT). In both mentioned models, the Lagrangians are constructed by a linear function of R and T .

Topological magnetic excitations

Abstract: Topological properties play an increasingly important role in future research and technology. This also applies to the field of topological magnetic excitations which has recently become a very active and broad field. In this Perspective article, we give an insight into the current theoretical and experimental investigations and try an outlook on future lines of research.

Measurement-device–independent quantum secure direct communication of multiple degrees of freedom of a single photon

Abstract: Quantum secure direct communication (QSDC) can realize the direct and secure transmission of information instead of sharing secure keys between two parties. Similar to quantum key distribution (QKD), in practical applications, QSDC may suffer from attacks from imperfect detector. Measurement-device–independent QSDC (MDI-QSDC) can remove all attacks at detector's side and close all loopholes in the detection system. However, existing MDI-QSDC protocols have relatively low capacity. In this paper, we propose a high-capacity MDI-QSDC protocol of multiple degrees of freedom of a single photon. Compared with original MDI-QSDC protocols, our protocol has larger channel capacity which can use a single photon to transmit multi-bit of secure information. This protocol may have potential application in future quantum secure communication.

A shortcut tour of quantum control methods for modern quantum technologies

Abstract: Quantum control methods, like rapid adiabatic passage, stimulated Raman adiabatic passage, shortcuts to adiabaticity and optimal control, have become an integral part of modern quantum technologies, for example quantum computation and sensing, where they are exploited in order to find the optimal pulse sequences which drive quantum systems to the desired target state in minimum time or with maximum fidelity, overcoming decoherence and dissipation. In this perspective, we use the basic example of adiabatic population inversion in a two-level system in order to present these methods and review the latest developments in the field, while we touch upon the emerging method of reinforcement learning.

Perspective on attractive-repulsive interactions in dynamical networks: Progress and future

Abstract: Emerging collective behavior in complex dynamical networks depends on both coupling function and underlying coupling topology. Through this perspective, we provide a brief yet profound excerpt of recent research efforts that explore how the synergy of attractive and repulsive interactions influence the destiny of ensembles of interacting dynamical systems. We review the incarnation of collective states ranging from chimera or solitary states to extreme events and oscillation quenching arising as a result of different network arrangements. Though the existing literature demonstrates that many of the crucial developments have been made, nonetheless, we come up with significant routes of further research in this field of study.

Non-Markovian out-of-equilibrium dynamics: A general numerical procedure to construct time-dependent memory kernels for coarse-grained observables

Abstract: We present a numerical method to compute non-equilibrium memory kernels based on experimental data or molecular dynamics simulations. The procedure uses a recasting of the non-stationary generalized Langevin equation, in which we expand the memory kernel in a series that can be reconstructed iteratively. Each term in the series can be computed based solely on knowledge of the two-time auto-correlation function of the observable of interest. As a proof of principle, we apply the method to crystallization from a super-cooled Lennard Jones melt. We analyze the nucleation and growth dynamics of crystallites and observe that the memory kernel has a time extent that is about one order of magnitude larger than the typical timescale needed for a particle to be attached to the crystallite in the growth regime.

Barrow's black hole entropy and the equipartition theorem

Abstract: The Barrow entropy appears from the fact that the black hole surface can be modified due to quantum gravitational outcome. The measure of this perturbation is given by a new exponent $\Delta$. In this letter we have shown that, from the standard mathematical form of the equipartition theorem, we can relate it with Barrow entropy. From this equivalence, we have calculated precisely the value of the exponent for the equipartition law. After that, we tested the thermodynamical coherence of the system by calculating the heat capacity which established an interval of the possible thermodynamical coherent values of Barrow entropic exponent and corroborated our first result.

Ultra-long-lived quasi-normal modes of neutron stars in massive scalar-tensor gravity

Abstract: The spectrum of frequencies and characteristic times that compose the ringdown phase of gravitational waves emitted by neutron stars carries information about the matter content (the equation of state) and the underlying theory of gravity. Typically, modified theories of gravity introduce additional degrees of freedom/fields, such as scalars, which result in new families of modes composing the ringdown spectrum. Simple but physically promising candidates are scalar-tensor theories, which effectively introduce an additional massive scalar field (i.e. , an ultra-light boson) that couples non-minimally to gravity, resulting in scalarized neutron stars. Here we present the first calculation of the full ringdown spectrum in such theories. We show that the ringdown spectrum of neutron stars with ultra-light bosons is much richer and fundamentally different from the spectrum in general relativity and that it possesses propagating ultra-long-lived modes.

Intrinsic piezoelectricity in monolayer MSi2N4 (M = Mo, W, Cr, Ti, Zr and Hf)

Abstract: Motived by experimentally synthesized (Hong Y. L. et al ., Science , 369 (2020) 670), the intrinsic piezoelectricity in monolayer ( , W, Cr, Ti, Zr and Hf) are studied by density functional theory (DFT). Among the six monolayers, has the best piezoelectric strain coefficient d 11 of 1.24 pm/V, and the second is 1.15 pm/V for . Taking as a example, strain engineering is applied to improve d 11 . It is found that tensile biaxial strain can enhance d 11 of , and the d 11 at 4% strain can improve by 107% with respect to the unstrained one. By replacing the N by P or As in , the d 11 can be raised substantially. For and , the d 11 is as high as 4.93 pm/V and 6.23 pm/V, which is mainly due to smaller and very small minus or positive ionic contribution to piezoelectric stress coefficient e 11 with respect to . The discovery of this piezoelectricity in monolayer enables active sensing, actuating and new electronic components for nanoscale devices, and is recommended for experimental exploration.

Velocity and diffusion constant of an active particle in a one-dimensional force field

Abstract: We consider a run an tumble particle with two velocity states $\pm v_0$, in an inhomogeneous force field $f(x)$ in one dimension. We obtain exact formulae for its velocity $V_L$ and diffusion constant $D_L$ for arbitrary periodic $f(x)$ of period $L$. They involve the "active potential" which allows to define a global bias. Upon varying parameters, such as an external force $F$, the dynamics undergoes transitions from non-ergodic trapped states, to various moving states, some with non analyticities in the $V_L$ versus $F$ curve. A random landscape in the presence of a bias leads, for large $L$, to anomalous diffusion $x \sim t^\mu$, $\mu<1$, or to a phase with a finite velocity that we calculate.

Eco-evolutionary dynamics with environmental feedback: Cooperation in a changing world

Abstract: Eco-evolutionary game dynamics which characterizes the mutual interactions and the coupled evolutions of strategies and environments has been of growing interests in very recent years. Since such feedback loops widely exist in a range of coevolutionary systems, such as microbial systems, social-ecological system and psychological-economic system, recent modeling frameworks that unveil the oscillating dynamics of social dilemmas have great potential for practical applications. In this perspective article, we overview the latest progress of evolutionary game theory in this direction. We describe both mathematical methods and interdisciplinary applications across different fields. The ideas worthy of further consideration are discussed in prospects, with the central role of promoting cooperations in a changing world.

Rydberg antiblockade regimes: Dynamics and applications

Abstract: Rydberg antiblockade (RAB) allows more than one Rydberg atom to be excited in the presence of Rydberg-Rydberg interaction (RRI) and has many potential applications in quantum optics, many-body physics and quantum information. In this paper, we would review the conditions and possible applications of different types of RAB regimes under weak, intermediate and strong RRIs, respectively. Both van der Waals (vdW) and dipole-dipole (DD) interactions are considered for each interaction strength. This work displays the layout of RAB and provides a reference for further study of RAB-regime-based quantum optics and quantum information processing tasks.

Conformal inflation in the metric-affine geometry

Abstract: Systematic understanding for classes of inflationary models is investigated from a viewpoint of the local conformal symmetry and the slightly broken global symmetry in the framework of the metric-affine geometry. In the metric-affine geometry, which is a generalization of the Riemannian one adopted in the ordinary General Relativity, the affine connection is an independent variable of the metric rather than given e.g. by the Levi-Civita connection as its function. Thanks to this independency, the metric-affine geometry can preserve the local conformal symmetry in each term of the Lagrangian contrary to the Riemannian geometry, and then the local conformal invariance can be compatible with much more kinds of global symmetries. As simple examples, we consider the two-scalar models with the broken $\mathrm{SO}(1,1)$ or $\mathrm{O}(2)$, leading to the well-known $\alpha$-attractor or natural inflation respectively. The inflaton can be understood as their pseudo Nambu-Goldstone boson.

Omnidirectional optical filtering based on two kinds of photonic band gaps with different angle-dependent properties

Abstract: Edge states in heterostructures composed of two kinds of all-dielectric one-dimensional photonic crystals (1DPCs) can be utilized for narrowband filtering. However, the filtering transmittance peak, along with the photonic band gaps (PBGs) of all-dielectric 1DPC, will shift toward short wavelengths (blueshift) as the incident angle increases. In this letter, we investigate the filtering property of the heterostructure composed of an all-dielectric 1DPC and a 1DPC containing hyperbolic metamaterials (HMMs). For the 1DPC containing HMMs, the PBG can be designed to be redshifted under TM polarization. Based on these two kinds of PBGs with different angle-dependent properties, omnidirectional filtering at a fixed wavelength range can be realized under TM polarization. This omnidirectional filter can be utilized for all-angle phase matching in coherent nonlinear optical process and angle-insensitive Rabi splitting.

Unifying topological phase transitions in non-interacting, interacting, and periodically driven systems

Abstract: Topological phase transitions track changes in topological properties of a system and occur in real materials as well as quantum engineered systems, all of which differ greatly in terms of dimensionality, symmetries, interactions, and driving, and hence require a variety of techniques and concepts to describe their topological properties. For instance, depending on the system, topology may be accessed from single-particle Bloch wave functions, Green's functions, or many-body wave functions. We demonstrate that despite this diversity, all topological phase transitions display a universal feature: namely, a divergence of the curvature function that composes the topological invariant at the critical point. This feature can be exploited via a renormalization-group-like methodology to describe topological phase transitions. This approach serves to extend notions of correlation function, critical exponents, scaling laws and universality classes used in Landau theory to characterize topological phase transitions in a unified manner.

Investigation of Unruh temperature of black holes by using the EGUP formalism

Abstract: In this paper, we have used the extended generalized uncertainty principle to investigate the Unruh temperature and thermodynamic properties of a black hole. We started with a brief perusal of the Heisenberg uncertainty principle and continue with some physical and mathematical discussion for obtaining the generalized and the extended generalized uncertainty principle. Then, we obtained the Unruh temperature, mass-temperature, specific heat, and entropy functions of a black hole. We enriched the paper with graphical analysis as well as their comparisons.

Quantum random access codes and incompatibility of measurements

Abstract: It is one of the peculiar features of quantum physics that some sets of measurements are incompatible in the sense that they cannot be performed simultaneously. Incompatibility is an important quantum resource as it enables Bell nonlocality and steering. Here we show that incompatibility is crucial also in certain communication tasks; we prove that quantum random access code performs better than its classical counterpart only when incompatible quantum measurements are used in the decoding task. As a consequence, evaluating the average success probability for quantum random access code provides a semi-device-independent test for the detection of quantum incompatibility. We further demonstrate that any incompatible pair of projective measurements gives an advantage over all classical strategies. Finally, we establish a connection between the maximal average success probability for quantum random access code and earlier quantities introduced to assess incompatibility.