Nonequilibrium Dynamics Of Collective Excitations In Quantum Materials

This book studies the dynamics of fundamental collective excitations in quantum materials, focusing on the use of state-of-the-art ultrafast broadband optical spectroscopy. Collective behaviour in solids lies at the origin of several cooperative phenomena that can lead to profound transformations, instabilities and phase transitions. Revealing the dynamics of collective excitations is a topic of pivotal importance in contemporary condensed matter physics, as it provides information on the strength and spatial distribution of interactions and correlation. The experimental framework explored in this book relies on setting a material out-of-equilibrium by an ultrashort laser pulse and monitoring the photo-induced changes in its optical properties over a broad spectral region in the visible or deep-ultraviolet. Collective excitations (e.g. plasmons, excitons, phonons...) emerge either in the frequency domain as spectral features across the probed range, or in the time domain as coherent modes triggered by the pump pulse. Mapping the temporal evolution of these collective excitations provides access to the hierarchy of low-energy phenomena occurring in the solid during its path towards thermodynamic equilibrium. This methodology is used to investigate a number of strongly interacting and correlated materials with an increasing degree of internal complexity beyond conventional band theory.

This book advances understanding of light-induced phase transitions and nonequilibrium orders that occur in a broken-symmetry system. Upon excitation with an intense laser pulse, materials can undergo a nonthermal transition through pathways different from those in equilibrium. The mechanism underlying these photoinduced phase transitions has long been researched, but many details in this ultrafast, non-adiabatic regime still remain to be clarified. The work in this book reveals new insights into this phenomena via investigation of photoinduced melting and recovery of charge density waves (CDWs). Using several time-resolved diffraction and spectroscopic techniques, the author shows that the light-induced melting of a CDW is characterized by dynamical slowing-down, while the restoration of the symmetry-breaking order features two distinct timescales: A fast recovery of the CDW amplitude is followed by a slower re-establishment of phase coherence, the latter of which is dictated by the presence of topological defects in the CDW. Furthermore, after the suppression of the original CDW by photoexcitation, a different, competing CDW transiently emerges, illustrating how a hidden order in equilibrium can be unleashed by a laser pulse. These insights into CDW systems may be carried over to other broken-symmetry states, such as superconductivity and magnetic ordering, bringing us one step closer towards manipulating phases of matter using a laser pulse.

The 1995 observation of Bose–Einstein condensation in dilute atomic vapours spawned the field of ultracold, degenerate quantum gases. Unprecedented developments in experimental design and precision control have led to quantum gases becoming the preferred playground for designer quantum many-body systems. This self-contained volume provides a broad overview of the principal theoretical techniques applied to non-equilibrium and finite temperature quantum gases. Covering Bose–Einstein condensates, degenerate Fermi gases, and the more recently realised exciton–polariton condensates, it fills a gap by linking between different methods with origins in condensed matter physics, quantum field theory, quantum optics, atomic physics, and statistical mechanics. Thematically organised chapters on different methodologies, contributed by key researchers using a unified notation, provide the first integrated view of the relative merits of individual approaches, aided by pertinent introductory chapters and the guidance of editorial notes. Both graduate students and established researchers wishing to understand the state of the art will greatly benefit from this comprehensive and up-to-date review of non-equilibrium and finite temperature techniques in the exciting and expanding field of quantum gases and liquids. Contents:Introductory Material:Quantum Gases: The BackgroundQuantum Gases: Experimental ConsiderationsQuantum Gases: Background Key Theoretical NotionsUltracold Bosonic Gases: Theoretical Modelling:Kinetic and Many-Body ApproachesClassical-Field, Stochastic and Field-Theoretic ApproachesComparison of Common TheoriesOverview of Related Quantum-Degenerate Systems:Nearly Integrable One-Dimensional SystemsOptical Lattice GeometriesLiquid HeliumDegenerate Fermi GasesExciton/Polariton Condensation Readership: Aimed at graduate level students and for researchers. Keywords:Quantum Gas;Bose–Einstein;Condensate;Mean Field;Classical Field;Quantum Dynamics;Cold Atom;Ultracold Atom;Superfluid;Non-Equilibrium;Kinetic Theory;Field Theory;Quantum Fluid;Quantum Liquid;Degenerate Gas;Quantum Statistics;Number-Conserving;Symmetry-Breaking;Finite Temperature;Fluctuations;Stochastic;Gross–Pitaevskii;Bogoliubov;Many Body;Phase-Space Methods;Low-Dimensional;Optical Lattice;Bose;Fermi;Exciton;Polariton;ThermalizationKey Features:This book provides a unique and editorially linked, impartial unified presentation of the leading theoretical models for quantum gases far from equilibrium, and at finite temperaturesIn addition to focusing on bosonic gases, this book also makes connections to related quantum gases and fluids, such as fermionic gases, atoms in optical lattices, as well as exciton and polariton condensatesIntroductory chapters make this book an essential, accessible resource to both graduate students and early researchers as well as established scientists, with individual chapters written and edited by prominent researchers in the fieldReviews:“This book should be the first reference point for learning about various theoretical approaches to describing quantum gases. The editors and contributors have created a unique book with well-written articles, meaningful comparisons of various approximation schemes, a uniform notation and more than one thousand references. In addition, the book features introductory chapters and up-to-date review articles of experimental methods and current frontiers. The completeness and depth of the presentation are impressive.”Wolfgang Ketterle, MIT-Harvard Center for Ultracold Atoms & Nobel Laureate

This thesis explores the physics of non-equilibrium quantum dynamics in homogeneous two-dimensional (2D) quantum gases. Ultracold quantum gases driven out of equilibrium have been prominent platforms for studying quantum many-body physics. However, probing non-equilibrium dynamics in conventionally trapped, inhomogeneous atomic quantum gases has been a challenging task because coexisting mass transport and spreading of quantum correlations often complicate experimental analyses. In this work, the author solves this technical hurdle by producing ultracold cesium atoms in a quasi-2D optical box potential. The exquisite optical trap allows one to remove density inhomogeneity in a degenerate quantum gas and control its dimensionality. The author also details the development of a high-resolution, in situ imaging technique to monitor the evolution of collective excitations and quantum transport down to atomic shot-noise, and at the length scale of elementary collective excitations. Meanwhile, tunable Feshbach resonances in ultracold cesium atoms permit precise and dynamical control of interactions with high temporal and even spatial resolutions. By employing these state-of-the-art techniques, the author performed interaction quenches to control the generation and evolution of quasiparticles in quantum gases, presenting the first direct measurement of quantum entanglement between interaction quench generated quasiparticle pairs in an atomic superfluid. Quenching to attractive interactions, this work shows stimulated emission of quasiparticles, leading to amplified density waves and fragmentation, forming 2D matter-wave Townes solitons that were previously considered impossible to form in equilibrium due to their instability. This thesis unveils a set of scale-invariant and universal quench dynamics and provides unprecedented tools to explore quantum entanglement transport in a homogenous quantum gas.

This book presents the proceedings of the course "Spectroscopy and Dynamics of Collective Excitations in Solids" held in Erice, Italy from June 17 to July 1, 1995. This meeting was organized by the International School of Atomic and Molecular Spectroscopy of the "Ettore Majorana" Centre for Scientific Culture. The purpose of this course was to present and discuss physical models, mathematical formalisms, experimental techniques and applications relevant to the subject of collective excitations in solids. By bringing together specialists in the field of solid state spectroscopy, this course provided a much needed forum for the critical assessment and evaluation of recent and past developments in the physics of solids. A total of 83 participants came from 57 laboratories and 20 different countries (Austria, Belgium, Brazil, Denmark, Finland, France, Germany, Greece, Israel, Italy, Japan, The Netherlands, Norway, Portugal, Russia, Spain, Switzerland, Turkey, the United Kingdom, and the United States). The secretaries of the course were Stamatios K yrkos and Daniel Di Bartolo. 45 lectures divided in 13 series were given. In addition 8 (one or two-hour) "long seminars," 1 "special lecture," 2 interdisciplinary lectures, 29 "short seminars," and 16 posters were presented. The sequence of lectures was in accordance with the logical development of the subject of the meeting. Each lecturer started at a rather fundamental level and ultimately reached the frontier of knowledge in the field.

This book studies the fundamental aspects of many-body physics in quantum systems open to an external world. Recent remarkable developments in the observation and manipulation of quantum matter at the single-quantum level point to a new research area of open many-body systems, where interactions with an external observer and the environment play a major role. The first part of the book elucidates the influence of measurement backaction from an external observer, revealing new types of quantum critical phenomena and out-of-equilibrium dynamics beyond the conventional paradigm of closed systems. In turn, the second part develops a powerful theoretical approach to study the in- and out-of-equilibrium physics of an open quantum system strongly correlated with an external environment, where the entanglement between the system and the environment plays an essential role. The results obtained here offer essential theoretical results for understanding the many-body physics of quantum systems open to an external world, and can be applied to experimental systems in atomic, molecular and optical physics, quantum information science and condensed matter physics.

This volume provides a broad overview of the principal theoretical techniques applied to non-equilibrium and finite temperature quantum gases. Covering Bose-Einstein condensates, degenerate Fermi gases, and the more recently realised exciton-polariton condensates, it fills a gap by linking between different methods with origins in condensed matter physics, quantum field theory, quantum optics, atomic physics, and statistical mechanics.

Advances in Imaging & Electron Physics merges two long-running serials—Advances in Electronics & Electron Physics and Advances in Optical & Electron Microscopy. The series features extended articles on the physics of electron devices (especially semiconductor devices), particle optics at high and low energies, microlithography, image science, and digital image processing, electromagnetic wave propagation, electron microscopy, and the computing methods used in all these domains. Contains contributions from leading authorities on the subject matter Informs and updates on all the latest developments in the field of imaging and electron physics Provides practitioners interested in microscopy, optics, image processing, mathematical morphology, electromagnetic fields, electron, and ion emission with a valuable resource Features extended articles on the physics of electron devices (especially semiconductor devices), particle optics at high and low energies, microlithography, image science. and digital image processing