Transport and Entanglement across Integrable Impurities from Generalized Hydrodynamics.

Quantum impurity models (QIMs) are ubiquitous throughout physics. As simplified toy models they provide crucial insights for understanding more complicated strongly correlated systems, while in their own right are accurate descriptions of many experimental platforms. In equilibrium, their physics is well understood and have proven a testing ground for many powerful theoretical tools, both numerical and analytical, in use today. Their nonequilibrium physics is much less studied and understood. However, the recent advancements in nonequilibrium integrable quantum systems through the development of generalized hydrodynamics (GHD) coupled with the fact that many archetypal QIMs are in fact integrable presents an enticing opportunity to enhance our understanding of these systems. We take a step towards this by expanding the framework of GHD to incorporate integrable interacting QIMs. We present a set of Bethe-Boltzmann type equations which incorporate the effects of impurity scattering and discuss the new aspects which include entropy production. These impurity GHD equations are then used to study a bipartioning quench wherein a relevant backscattering impurity is included at the location of the bipartition. The density and current profiles are studied as a function of the impurity strength and expressions for the entanglement entropy and full counting statistics are derived.

Solution of the BEC to BCS Quench in One Dimension.

A gas of interacting fermions confined in a quasi one-dimensional geometry shows a BEC to BCS crossover upon slowly driving its coupling constant through a confinement-induced resonance. On one side of the crossover the fermions form tightly bound bosonic molecules behaving as a repulsive Bose gas, while on the other they form Cooper pairs, whose size is much larger than the average interparticle distance. Here we consider the situation arising when the coupling constant is varied suddenly from the BEC to the BCS value. Namely, we study a BEC-to-BCS quench. By exploiting a suitable continuum limit of recently discovered solvable quenches in the Hubbard model, we show that the local stationary state reached at large times after the quench can be determined exactly by means of the quench action approach. We provide an experimentally accessible characterization of the stationary state by computing local pair correlation function as well as the quasiparticle distribution functions. We find that the steady state is increasingly dominated by two-particle spin singlet bound states for stronger interaction strength, but that bound state formation is inhibited at larger BEC density. The bound state rapidity distribution displays quartic power-law decay suggesting a violation of Tan's contact relations.

Nonequilibrium Full Counting Statistics and Symmetry-Resolved Entanglement from Space-Time Duality.

Owing to its probabilistic nature, a measurement process in quantum mechanics produces a distribution of possible outcomes. This distribution-or its Fourier transform known as full counting statistics (FCS)-contains much more information than say the mean value of the measured observable, and accessing it is sometimes the only way to obtain relevant information about the system. In fact, the FCS is the limit of an even more general family of observables-the charged moments-that characterize how quantum entanglement is split in different symmetry sectors in the presence of a global symmetry. Here we consider the evolution of the FCS and of the charged moments of a U(1) charge truncated to a finite region after a global quantum quench. For large scales these quantities take a simple large-deviation form, showing two different regimes as functions of time: while for times much larger than the size of the region they approach a stationary value set by the local equilibrium state, for times shorter than region size they show a nontrivial dependence on time. We show that, whenever the initial state is also U(1) symmetric, the leading order in time of FCS and charged moments in the out-of-equilibrium regime can be determined by means of a space-time duality. Namely, it coincides with the stationary value in the system where the roles of time and space are exchanged. We use this observation to find some general properties of FCS and charged moments out of equilibrium, and to derive an exact expression for these quantities in interacting integrable models. We test this expression against exact results in the Rule 54 quantum cellular automaton and exact numerics in the XXZ spin-1/2 chain.

Optical coherence tomography versus other biomarkers: Associations with physical and cognitive disability in multiple sclerosis.

BACKGROUND: Optical coherence tomography (OCT) is a biomarker of neuroaxonal loss in multiple sclerosis (MS). OBJECTIVE: The objective was to assess the relative role of OCT, next to magnetic resonance imaging (MRI) and serum markers of disability in MS. METHODS: A total of 100 patients and 52 controls underwent OCT to determine peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell-inner plexiform layers (GCIPL). Serum neurofilament light chain (sNfL), total lesion volume (TLV), and brain parenchymal fraction (BPF) were also assessed. The associations of OCT with disability were examined in linear regression models with correction for age, vision, and education. RESULTS: In patients, pRNFL was associated with the Symbol Digit Modalities Test (SDMT; p = 0.030). In the multivariate analysis including sNfL and MRI measures, pRNFL (ß = 0.19, p = 0.044) and TLV (ß = -0.24, p = 0.023) were the only markers associated with the SDMT. pRNFL (p < 0.001) and GCIPL (p < 0.001) showed associations with the Expanded Disability Status Scale (EDSS). In the multivariate analysis, GCIPL showed the strongest association with the EDSS (ß = -0.32, p < 0.001) followed by sNfL (ß = 0.18, p = 0.024). CONCLUSION: The associations of OCT measures with cognitive and physical disability were independent of serum and brain MRI markers of neuroaxonal loss. OCT can be an important tool for stratification in MS, while longitudinal studies using combinations of biomarkers are warranted.

Negativity Hamiltonian: An Operator Characterization of Mixed-State Entanglement.

In the context of ground states of quantum many-body systems, the locality of entanglement between connected regions of space is directly tied to the locality of the corresponding entanglement Hamiltonian: the latter is dominated by local, few-body terms. In this work, we introduce the negativity Hamiltonian as the (non-Hermitian) effective Hamiltonian operator describing the logarithm of the partial transpose of a many-body system. This allows us to address the connection between entanglement and operator locality beyond the paradigm of bipartite pure systems. As a first step in this direction, we study the structure of the negativity Hamiltonian for fermionic conformal field theories and a free-fermion chain: in both cases, we show that the negativity Hamiltonian assumes a quasilocal functional form, that is captured by simple functional relations.

Postquantum Quench Growth of Renyi Entropies in Low-Dimensional Continuum Bosonic Systems.

The growth of Renyi entropies after the injection of energy into a correlated system provides a window upon the dynamics of its entanglement properties. We develop here a simulation scheme by which this growth can be determined in Luttinger liquids systems with arbitrary interactions, even those introducing gaps into the liquid. We apply this scheme to an experimentally relevant quench in the sine-Gordon field theory. While for short times we provide analytic expressions for the growth of the second and third Renyi entropy, to access longer times, we combine our scheme with truncated spectrum methods.

Pathophysiological Abnormalities in Migraine Ameliorated by Ketosis: A Proof-of-Concept Review.

Migraine is a prevalent heterogeneous neurological disorder, enumerated as the eighth most disabling neurological disorder by the World Health Organization. The growing advancement in technology and investigation of various facets of cerebral metabolism in migraine has shed light to metabolic mechanisms in migraine pathophysiology. A growing number of clinical research postulates migraine as a reaction to oxidative stress levels that go beyond antioxidant capacity or cerebral energy deficiency. This has become an extremely attractive subject area and over the past years there has also been a sustained research activity in using ketone bodies (KB) as a novel potential migraine prophylaxis. Not much epidemiological research has been conducted to exhibit the efficacy of ketone bodies in abnormal metabolism in migraine pathophysiology. Therefore, a better understanding of ketone bodies in metabolic migraine may provide novel therapeutic opportunities. The goal of this review is to assess present understanding on potential migraine triggers, as well as how ketogenic interventions support metabolic disability in migraines and address the therapeutic importance of ketones in migraine treatment, accenting clinical studies (including neuroimaging and therapeutic studies). This review is intended to demonstrate existing literature on the effects of ketone bodies on metabolic migraine traits to guide the readership through current concepts and foster a perspective for future research.

Baseline characteristics and effects of fingolimod on cognitive performance in patients with relapsing-remitting multiple sclerosis.

BACKGROUND AND PURPOSE: Studies reporting the baseline determinants of cognitive performance and treatment effect on cognition in patients with multiple sclerosis (MS) are limited. We investigated the baseline correlates of cognition and the long-term treatment effects of fingolimod 0.5 mg once daily on cognitive processing speed and attention in patients with relapsing-remitting MS. METHODS: This post hoc analysis pooled data from the phase 3 FREEDOMS and FREEDOMS II trials (N = 1556). We assessed the correlation between baseline patient demographic and disease characteristics and baseline 3-second Paced Auditory Serial Addition Test (PASAT-3) scores (Spearman's rank test) and the changes from baseline in PASAT-3 (mixed model repeated measures model) in the fingolimod and placebo (up to 24 months) or placebo-fingolimod switched (from Month 24 up to 120 months) groups. Additionally, the predictive value of PASAT-3 score for future disease outcomes was assessed (Cox or logistic regression models). RESULTS: Among the variables assessed, lower PASAT-3 score at baseline correlated with higher disease burden (total brain volume, T2 lesion volume, and Expanded Disability Status Scale score), longer disease duration and older age (p < 0.0001 for all). Fingolimod significantly improved PASAT-3 scores from baseline versus placebo at 6 (1.3; p = 0.0007), 12 (1.1; p = 0.0044) and 24 months (1.1; p = 0.0028), with a sustained effect (overall treatment effect p = 0.0012) up to 120 months. Improvements were seen regardless of baseline cognitive status (PASAT quartile). Baseline PASAT-3 score was predictive of both clinical and magnetic resonance imaging measures of disease activity at Month 24 (p < 0.001 for all). CONCLUSION: Early fingolimod treatment may offer long-term cognitive benefit in patients with relapsing-remitting MS.

Comparing underlying mechanisms of depression in multiple sclerosis and rheumatoid arthritis.

Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA) are common, chronic, autoimmune diseases affecting many people worldwide. While clinically very different in their phenotype, both diseases are thought to have an autoimmune-mediated origin. MS and RA share genetic similarities, and in both diseases, antibodies against host antigens can be found. Aside from the well-known somatic symptoms, many RA patients also show signs and symptoms of psychiatric illnesses, of which depression is the most common diagnosis. In this commentary, both diseases will be introduced and briefly characterized individually and then compared. Depression will be introduced as one of the most frequent psychiatric diseases in the general population. This paper focuses on presenting the possible causes, including psychosocial factors, genetics, and immunologic mechanisms. Hypotheses aimed to explain the higher incidence of depression in these two seemingly different autoimmune diseases will be discussed.

The assessment of cognitive and behavioural disturbances in vascular cognitive impairment (VCI) - recommendations of an expert working group.

With newer research-based classification systems, the term Vascular Cognitive Impairment (VCI) is now preferred to vascular dementia. VCI is an umbrella term that includes all forms of cognitive deficits ranging from mild cognitive impairment of vascular origin (VaMCI) to vascular dementia (VaD). The new VCI construct takes into account the fact that in addition to single strategic infarcts, multiple infarcts, and leukoaraiosis, there are other mechanisms of cerebrovascular disease such as chronic hypoperfusion that might account for the pattern of cognitive deficits associated with vascular dementia. The key to defining the spectrum of VCI is neuropsychological testing, bedside or office-based clinical examination, and neuroimaging. The lack of specific cognitive tools that are sufficiently sensitive to detect subtle deficits makes the assessment of cognitive impairment difficult. Prospective cross-sectional and longitudinal studies of VCI from different settings are therefore required. Although there have been few published reports, behavioural and psychological symptoms (BPS) are inherently present in VCI from the onset and during the course of the disease. Besides the type of population (i.e. clinical, community or nursing-home settings), the definition of VCI/VaD and the instruments used, and differences in the prevalence and pattern of BPS between various studies, could be due to other, often unconsidered, factors such as gender, age, education, use of medication and VCI/VaD severity.

Quantum Generalized Hydrodynamics.

Physical systems made of many interacting quantum particles can often be described by Euler hydrodynamic equations in the limit of long wavelengths and low frequencies. Recently such a classical hydrodynamic framework, now dubbed generalized hydrodynamics (GHD), was found for quantum integrable models in one spatial dimension. Despite its great predictive power, GHD, like any Euler hydrodynamic equation, misses important quantum effects, such as quantum fluctuations leading to nonzero equal-time correlations between fluid cells at different positions. Focusing on the one-dimensional gas of bosons with delta repulsion, and on states of zero entropy, for which quantum fluctuations are larger, we reconstruct such quantum effects by quantizing GHD. The resulting theory of quantum GHD can be viewed as a multicomponent Luttinger liquid theory, with a small set of effective parameters that are fixed by the thermodynamic Bethe ansatz. It describes quantum fluctuations of truly nonequilibrium systems where conventional Luttinger liquid theory fails.

Mixed-State Entanglement from Local Randomized Measurements.

We propose a method for detecting bipartite entanglement in a many-body mixed state based on estimating moments of the partially transposed density matrix. The estimates are obtained by performing local random measurements on the state, followed by postprocessing using the classical shadows framework. Our method can be applied to any quantum system with single-qubit control. We provide a detailed analysis of the required number of experimental runs, and demonstrate the protocol using existing experimental data [Brydges et al., Science 364, 260 (2019)SCIEAS0036-807510.1126/science.aau4963].

How do patients enter the healthcare system after the first onset of multiple sclerosis symptoms? The influence of setting and physician specialty on speed of diagnosis.

BACKGROUND: Diagnosing multiple sclerosis (MS) early is crucial to avoid future disability. However, potentially preventable delays in the diagnostic cascade from contact with a physician to definite diagnosis still occur and their causes are still unclear. OBJECTIVE: To identify the possible causes of delays in the diagnostic process. METHODS: We analyzed the data of the Swiss MS Registry. With logistic regression, we modeled the time from the first contact to the first consultation (contact-to-evaluation time, ⩽1 month/>1 month) and the evaluation-to-diagnosis time (⩽6 months/>6 months). Potential factors were health system characteristics, sociodemographic variables, first symptoms, and MS type. RESULTS: We included 522 participants. Mostly, general practitioners (67%) were contacted first, without delaying the diagnosis. In contrast, first symptoms and MS type were the major contributors to delays: gait problems were associated with longer contact-to-evaluation times, depression as a concomitant symptom with longer evaluation-to-diagnosis times, and having primary progressive MS prolonged both phases. In addition, living in mountainous areas was associated with longer contact-to-evaluation times, whereas diagnosis after 2000 was associated with faster diagnoses. CONCLUSION: For a quicker diagnosis, awareness of MS as a differential diagnosis of gait disorders and the co-occurrence of depression at onset should be raised, and these symptoms should be attentively followed.

Entanglement and thermodynamics after a quantum quench in integrable systems.

Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics. Recently, the study of quantum quenches revealed that these concepts are intricately intertwined. Although the unitary time evolution ensuing from a pure state maintains the system at zero entropy, local properties at long times are captured by a statistical ensemble with nonzero thermodynamic entropy, which is the entanglement accumulated during the dynamics. Therefore, understanding the entanglement evolution unveils how thermodynamics emerges in isolated systems. Alas, an exact computation of the entanglement dynamics was available so far only for noninteracting systems, whereas it was deemed unfeasible for interacting ones. Here, we show that the standard quasiparticle picture of the entanglement evolution, complemented with integrability-based knowledge of the steady state and its excitations, leads to a complete understanding of the entanglement dynamics in the space-time scaling limit. We thoroughly check our result for the paradigmatic Heisenberg chain.

Subsystem Trace Distance in Quantum Field Theory.

We develop a systematic method to calculate the trace distance between two reduced density matrices in 1+1 dimensional quantum field theories. The approach exploits the path integral representation of the reduced density matrices and an ad hoc replica trick. We then extensively apply this method to the calculation of the distance between reduced density matrices of one interval of length ℓ in eigenstates of conformal field theories. When the interval is short, using the operator product expansion of twist operators, we obtain a universal form for the leading order in ℓ of the trace distance. We compute the trace distances among the reduced density matrices of several low lying states in two-dimensional free massless boson and fermion theories. We compare our analytic conformal results with numerical calculations in XX and Ising spin chains finding perfect agreement.

Universal Broadening of the Light Cone in Low-Temperature Transport.

We consider the low-temperature transport properties of critical one-dimensional systems that can be described, at equilibrium, by a Luttinger liquid. We focus on the prototypical setting where two semi-infinite chains are prepared in two thermal states at small but different temperatures and suddenly joined together. At large distances x and times t, conformal field theory characterizes the energy transport in terms of a single light cone spreading at the sound velocity v. Energy density and current take different constant values inside the light cone, on its left, and on its right, resulting in a three-step form of the corresponding profiles as a function of ζ=x/t. Here, using a nonlinear Luttinger liquid description, we show that for generic observables this picture is spoiled as soon as a nonlinearity in the spectrum is present. In correspondence of the transition points x/t=±v, a novel universal region emerges at infinite times, whose width is proportional to the temperatures on the two sides. In this region, expectation values have a different temperature dependence and show smooth peaks as a function of ζ. We explicitly compute the universal function describing such peaks. In the specific case of interacting integrable models, our predictions are analytically recovered by the generalized hydrodynamic approach.

Exact Local Correlations and Full Counting Statistics for Arbitrary States of the One-Dimensional Interacting Bose Gas.

We derive exact analytic expressions for the n-body local correlations in the one-dimensional Bose gas with contact repulsive interactions (Lieb-Liniger model) in the thermodynamic limit. Our results are valid for arbitrary states of the model, including ground and thermal states, stationary states after a quantum quench, and nonequilibrium steady states arising in transport settings. Calculations for these states are explicitly presented and physical consequences are critically discussed. We also show that the n-body local correlations are directly related to the full counting statistics for the particle-number fluctuations in a short interval, for which we provide an explicit analytic result.

The Swiss Multiple Sclerosis Registry (SMSR): study protocol of a participatory, nationwide registry to promote epidemiological and patient-centered MS research.

BACKGROUND: Multiple sclerosis (MS) is one of the most frequently observed neurological conditions in Switzerland, but data sources for country-wide epidemiological trend monitoring are lacking. Moreover, while clinical and laboratory MS research are generally well established, there is a gap in patient-centered MS research to inform care management, or treatment decisions and policy making not only in Switzerland but worldwide. METHODS: In light of these research gaps, the Swiss Multiple Sclerosis Society initiated and funded the Swiss Multiple Sclerosis Registry (SMSR) an open-ended, longitudinal and prospective, nationwide, patient-centered study. The SMSR recruits adult persons with a suspected or confirmed MS diagnosis who reside or receive care in Switzerland. The SMSR has established a governance structure with clear rules and guidelines. It follows a citizen-science approach with direct involvement of persons with MS (PwMS), who contribute actively to registry development, operations, and research. Main scientific goals entail the study of MS epidemiology in Switzerland, health care access and provision, as well as life circumstances and wellbeing of persons with MS. The innovative study design ("layer model") offers several participation options with different time commitments. Data collection is by means of regular surveys and medical record abstraction. Survey participation is offered in different modes (web, paper & pencil) and in the three main national languages (German, French, Italian). Participants also receive regular data feedbacks for personal use and self-monitoring, contextualized in the whole population of study participants. Data feedbacks are also used to solicit data corrections of key variables from participants. DISCUSSION: The SMSR combines the advantages of traditional and novel research methods in medical research and has recruited over 1600 PwMS in its first year. The future-oriented design and technology will enable a response not only to future technological innovations and research trends, but also to challenges in health care provision for MS. TRIAL REGISTRATION: ClinicalTrials.gov NCT02980640 ; December 6, 2016; retrospectively registered.

New insights into the burden and costs of multiple sclerosis in Europe: Results for Switzerland.

INTRODUCTION: To estimate the value of interventions in multiple sclerosis (MS) - where lifetime costs and outcomes cannot be observed - outcome data have to be combined with costs. This requires that cost data be regularly updated. OBJECTIVES AND METHODS: This study is part of a cross-sectional retrospective study in 16 countries collecting data on resource consumption and work capacity, health-related quality of life (HRQoL) and prevalent symptoms for patients with MS. Descriptive analyses are presented by level of severity, from the societal perspective, in CHF 2015. RESULTS: A total of 721 patients (mean age 48 years) participated in Switzerland; 90% were below retirement age, and of these, 65% were employed. Employment was related to disease severity, and MS affected productivity at work for 69% of patients. Overall, 93% and 64% of patients experienced fatigue and cognition as a problem, respectively. The mean utility and annual costs were 0.799 and 29,600CHF at Expanded Disability Status Scale (EDSS) 0-3, 0.614 and 66,800CHF at EDSS 4-6.5 and 0.348 and 110,800CHF at EDSS 7-9, respectively. The mean cost of a relapse was estimated at 7600CHF. CONCLUSION: This study provides current data on MS in Switzerland that are important for development of health policies and to estimate the value of current and future treatments.

Multiparticle Bound-State Formation following a Quantum Quench to the One-Dimensional Bose Gas with Attractive Interactions.

We consider quantum quenches from an ideal Bose condensate to the Lieb-Liniger model with an arbitrary attractive interaction strength. We focus on the properties of the stationary state reached at late times after the quench. Using recently developed methods based on integrability, we obtain an exact description of the stationary state for a large number of bosons. A distinctive feature of this state is the presence of a hierarchy of multiparticle bound states. We determine the dependence of their densities on interaction strength and obtain an exact expression for the stationary value of the local pair correlation g_{2}. We discuss ramifications of our results for cold atom experiments.