Many-body localization beyond eigenstates in all dimensions

Isolated quantum systems with quenched randomness exhibit many-body localization (MBL), wherein they do not reach local thermal equilibrium even when highly excited above their ground states. It is widely believed that individual eigenstates capture this breakdown of thermalization at finite size. We show that this belief is false in general and that a MBL system can exhibit the eigenstate properties of a thermalizing system. We propose that localized approximately conserved operators (l$^*$-bits) underlie localization in such systems. In dimensions $d>1$, we further argue that the existing MBL phenomenology is unstable to boundary effects and gives way to l$^*$-bits. Physical consequences of l$^*$-bits include the possibility of an eigenstate phase transition within the MBL phase unrelated to the dynamical transition in $d=1$ and thermal eigenstates at all parameters in $d>1$. Near-term experiments in ultra-cold atomic systems and numerics can probe the dynamics generated by boundary layers and emergence of l$^*$-bits.Comment: 12 pages, 5 figure

Thermal inclusions: how one spin can destroy a many-body localized phase

Many-body localized (MBL) systems lie outside the framework of statistical mechanics, as they fail to equilibrate under their own quantum dynamics. Even basic features of MBL systems such as their stability to thermal inclusions and the nature of the dynamical transition to thermalizing behavior remain poorly understood. We study a simple model to address these questions: a two level system interacting with strength $J$ with $N\gg 1$ localized bits subject to random fields. On increasing $J$, the system transitions from a MBL to a delocalized phase on the \emph{vanishing} scale $J_c(N) \sim 1/N$, up to logarithmic corrections. In the transition region, the single-site eigenstate entanglement entropies exhibit bi-modal distributions, so that localized bits are either "on" (strongly entangled) or "off" (weakly entangled) in eigenstates. The clusters of "on" bits vary significantly between eigenstates of the \emph{same} sample, which provides evidence for a heterogenous discontinuous transition out of the localized phase in single-site observables. We obtain these results by perturbative mapping to bond percolation on the hypercube at small $J$ and by numerical exact diagonalization of the full many-body system. Our results imply the MBL phase is unstable in systems with short-range interactions and quenched randomness in dimensions $d$ that are high but finite.Comment: 17 pages, 12 figure

Stratospheric sudden warming effects on winds and temperature in the middle atmosphere at middle and low latitudes: a study using WACCM

A stratospheric sudden warming (SSW) is a dynamical phenomenon of the wintertime stratosphere caused by the interaction between planetary Rossby waves propagating from the troposphere and the stratospheric zonal-mean flow. While the effects of SSW events are seen predominantly in high latitudes, they can also produce significant changes in middle and low latitude temperature and winds. In this study we quantify the middle and low latitude effects of SSW events on temperature and zonal-mean winds using a composite of SSW events between 1988 and 2010 simulated with the specified dynamics version of the Whole Atmosphere Community Climate Model (WACCM). The temperature and wind responses seen in the tropics also extend into the low latitudes in the other hemisphere. There is variability in observed zonal-mean winds and temperature depending on the observing location within the displaced or split polar vortex and propagation direction of the planetary waves. The propagation of planetary waves show that they originate in mid–high latitudes and propagate upward and equatorward into the mid-latitude middle atmosphere where they produce westward forcing reaching peak values of ~ 60–70 m s⁻¹ day⁻¹. These propagation paths in the lower latitude stratosphere appear to depend on the phase of the quasi-biennial oscillation (QBO). During the easterly phase of the QBO, waves originating at high latitudes propagate across the equator, while in the westerly phase of the QBO, the planetary waves break at ~ 20–25° N and there is no propagation across the equator. The propagation of planetary waves across the equator during the easterly phase of the QBO reduces the tropical upwelling and poleward flow in the upper stratosphere

Emergent Coulombic criticality and Kibble-Zurek scaling in a topological magnet

When a classical system is driven through a continuous phase transition, its nonequilibrium response is universal and exhibits Kibble-Zurek scaling. We explore this dynamical scaling in the novel context of a three-dimensional topological magnet with fractionalized excitations, namely the liquid-gas transition of the emergent mobile magnetic monopoles in dipolar spin ice. Using field-mixing and finite-size scaling techniques, we place the critical point of the liquid-gas line in the three-dimensional Ising universality class. We then demonstrate Kibble-Zurek scaling for sweeps of the magnetic field through the critical point. Unusually slow microscopic time scales in spin ice offer a unique opportunity to detect this universal nonequilibrium physics in current experimental setups.This work was supported in part by Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/G049394/1 (C.C.), the Helmholtz Virtual Institute “New States of Matter and Their Excitations,” and the EPSRC NetworkPlus on “Emergence and Physics far from Equilibrium.” Research at Perimeter Institute is supported by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Economic Development and Innovation. The calculations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/) and the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk/, for which access was provided by the ARCHER Driving Test scheme). The authors are grateful to A. Sandvik for useful discussions and to S. L. Sondhi for advice and collaboration on several pieces of related work. J.O.H. is grateful to the EPSRC for funding, and to Michael Rutter for computing support.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.92.07514

Nanosecond pulsed 620 nm source by frequency-doubling a phosphosilicate Raman fiber amplifier

We demonstrate a nanosecond pulsed source at 620 nm with watt-level average power by frequency-doubling a 1240 nm phosphosilicate Raman fiber amplifier. A gain-switched laser diode operating at 1064 nm is amplified in an ytterbium fiber master oscillator power amplifier system and then converted to 1240 nm using a phosphosilicate Raman fiber amplifier with a conversion efficiency of up to 66%. The Raman fiber amplifier is seeded with a continuous-wave 1240 nm laser diode to obtain narrow-linewidth radiation, which is subsequently frequency-doubled in a periodically poled lithium tantalate crystal. A maximum average power of 1.5 W is generated at 620 nm, corresponding to a pulse energy of 300 nJ at a repetition rate of 5 MHz. The source has excellent beam quality (M2≤1.16) and an optical efficiency (1064 nm to 620 nm) of 20%, demonstrating an effective architecture for generating red pulsed light for biomedical imaging applications

Влияние национального локдауна на эпидемиологию травм во время первой волны COVID-19 в Индии

Background. The pattern of hospital admissions and medical care changed during the COVID pandemic. The aim of the study to describe the nature of patients attending the orthopedic emergency department of a level 1 trauma center in terms of number and proportion based on demographic characteristics and the nature of the injury before the lockdown, during the lockdown, and during the unlocking period of the nationwide lockdown for controlling the COVID-19 pandemic in India. Methods. We conducted a longitudinal study from 01.01.2020 to 31.12.2020. Patients attending the orthopedic emergency were grouped based on cause, type, and site of injury. The median number observed each day with IQR. The distribution of the same was compared between the prelockdown with lockdown period and the lockdown period with a phased unlocking period. Results. A total of 10513 patients were included. There was a statistically significant reduction in the proportion of patients needing inpatient care between the prelockdown phase and lockdown phase (p = 0.008). However, this was not seen between lockdown and postlockdown periods (p = 0.47). The proportion of road traffic accidents dropped from 26% to 15% during this time (p0.001). The proportion of contusions was reduced and that of soft tissue injuries increased (p0.001). The proportion of lower limb injuries decreased from the prelockdown phase to the lockdown phase, and that of spinal injury patients increased (p = 0.007). The proportion of patients with contusions increased and soft tissue injuries decreased during this period (p0.001). Lower limb injuries and road traffic accidents increased, and spinal injuries were reduced (p0.001). Conclusion. The lockdown for controlling the spread of the pandemic affected the demographic and epidemiological aspects of injuries attending the orthopedic emergency department of a level 1 trauma center in a developing country. There was a decrease in the proportion of females and children attending the ED during the lockdown. The number of road traffic accedents s decreased during the lockdown. The number of patients with contusions attending the trauma center during the lockdown decreased, but there was an increase in the number of patients with spine injuries. We suggest that improvement in triage facilities, wider use of telemedicine, and increasing the stock of PPEs are essential for tackling such situations in the future.Введение. Во время пандемии COVID-19 изменилась структура госпитализаций и оказания медицинской помощи. Цель проанализировать эпидемиологию и тип травм, полученных пациентами, обратившимися в травмоцентр 1-го уровня во время пандемии и локдауна в Индии. Материал и методы. Мы провели лонгитюдное исследование с 01.01.2020 по 31.12.2020 Пациенты, обратившиеся за неотложной травматологической помощью, были сгруппированы в зависимости от причины, типа и места повреждения. Среднее число ежедненых обращений было расчитано с помощью IQR (интерквартильного размаха). Было проведено сравнение распределений среднего числа наблюдений между периодами до и во время локдауна, а также во время локдауна и после его снятия. Результаты. Всего в исследование было включено 10 513 пациентов. Наблюдалось статистически значимое снижение доли пациентов, нуждающихся в госпитализации, между периодами до и во время локдауна (p = 0,008). Однако этого не наблюдалось между периодами локдауна и постлокдауна (p = 0,47). Доля дорожно-транспортных происшествий снизилась с 26% до 15% между периодами до и во время локдауна (p0,001). Доля ушибов уменьшилась, а мягкотканных повреждений увеличилась (p0,001). Доля травм нижних конечностей уменьшилась между периодами до и во время локдауна, а доля травм позвоночника увеличилась (p = 0,007). Заключение. Национальный локдаун повлиял на демографические и эпидемиологические показатели травм в травмоцентре 1-го уровня в Индии. Наблюдалось снижение доли женщин и детей, обратившихся в отделение неотложной помощи. Количество ДТП сократилось во время локдауна. Количество пациентов с ушибами, обратившихся в травматологический центр во время локдауна уменьшилось, а количество пациентов с травмами позвоночника увеличилось. Мы рекомендуем улучшить медицинскую сортировку, расширить использование телемедицины и увеличить запасы средств индивидуальной защиты для борьбы с подобными ситуациями в будущем