Pub Date : 2022-12-08DOI: 10.1146/annurev-conmatphys-040721-021331
A. Alexandradinata, L. Glazman
The modern scope of fermiology encompasses not just the classical geometry of Fermi surfaces but also the geometry of quantum wave functions over the Fermi surface. This enlarged scope is motivated by the advent of topological metals—metals whose Fermi surfaces are characterized by a robustly nontrivial Berry phase. We review the extent to which topological metals can be diagnosed from magnetic-field-induced quantum oscillations of transport and thermodynamic quantities. A holistic analysis of the oscillatory wave form is proposed, in which different characteristics of the wave form (e.g., phase offset, high-harmonic amplitudes, temperature-dependent frequency) encode different aspects of a topologically nontrivial Fermi surface. Which characteristic to focus on depends on ( a) the orientation of the magnetic field relative to certain crystallographic axes, ( b) the symmetry class of the topological metal, and ( c) the separation of Fermi-surface pockets in quasimomentum k space. Closely proximate pockets arise when (1) spin–split pockets are nearly overlapping due to a weak spin–orbit force or when (2) two pockets touch at an isolated k point, which can be a topological band-touching point or a saddlepoint in the energy-momentum dispersion. The emergence of a pseudospin degree of freedom (in case 1) and the implications of magnetic breakdown (in case 2) are reviewed, with emphasis on new aspects originating from the (nonabelian) Berry connection of the Fermi surface. Future extensions of topofermiology are suggested in the directions of interaction-induced Fermi-liquid instabilities and two-dimensional electron liquids. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Fermiology of Topological Metals","authors":"A. Alexandradinata, L. Glazman","doi":"10.1146/annurev-conmatphys-040721-021331","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040721-021331","url":null,"abstract":"The modern scope of fermiology encompasses not just the classical geometry of Fermi surfaces but also the geometry of quantum wave functions over the Fermi surface. This enlarged scope is motivated by the advent of topological metals—metals whose Fermi surfaces are characterized by a robustly nontrivial Berry phase. We review the extent to which topological metals can be diagnosed from magnetic-field-induced quantum oscillations of transport and thermodynamic quantities. A holistic analysis of the oscillatory wave form is proposed, in which different characteristics of the wave form (e.g., phase offset, high-harmonic amplitudes, temperature-dependent frequency) encode different aspects of a topologically nontrivial Fermi surface. Which characteristic to focus on depends on ( a) the orientation of the magnetic field relative to certain crystallographic axes, ( b) the symmetry class of the topological metal, and ( c) the separation of Fermi-surface pockets in quasimomentum k space. Closely proximate pockets arise when (1) spin–split pockets are nearly overlapping due to a weak spin–orbit force or when (2) two pockets touch at an isolated k point, which can be a topological band-touching point or a saddlepoint in the energy-momentum dispersion. The emergence of a pseudospin degree of freedom (in case 1) and the implications of magnetic breakdown (in case 2) are reviewed, with emphasis on new aspects originating from the (nonabelian) Berry connection of the Fermi surface. Future extensions of topofermiology are suggested in the directions of interaction-induced Fermi-liquid instabilities and two-dimensional electron liquids. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42500415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-11-30DOI: 10.1146/annurev-conmatphys-031620-100450
Alessandro Corbetta, F. Toschi
Understanding the behavior of human crowds is a key step toward a safer society and more livable cities. Despite the individual variability and will of single individuals, human crowds, from dilute to dense, invariably display a remarkable set of universal features and statistically reproducible behaviors. Here, we review ideas and recent progress in employing the language and tools from physics to develop a deeper understanding about the dynamics of pedestrians. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Physics of Human Crowds","authors":"Alessandro Corbetta, F. Toschi","doi":"10.1146/annurev-conmatphys-031620-100450","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-031620-100450","url":null,"abstract":"Understanding the behavior of human crowds is a key step toward a safer society and more livable cities. Despite the individual variability and will of single individuals, human crowds, from dilute to dense, invariably display a remarkable set of universal features and statistically reproducible behaviors. Here, we review ideas and recent progress in employing the language and tools from physics to develop a deeper understanding about the dynamics of pedestrians. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43739757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-11-29DOI: 10.1146/annurev-conmatphys-031620-100957
Arunima K. Singh, R. Gorelik, T. Biswas
The solar–to–chemical energy conversion of Earth-abundant resources like water or greenhouse gas pollutants like CO2 promises an alternate energy source that is clean, renewable, and environmentally friendly. The eventual large-scale application of such photo-based energy conversion devices can be realized through the discovery of novel photocatalytic materials that are efficient, selective, and robust. In the past decade, the Materials Genome Initiative has led to a major leap in the development of materials databases, both computational and experimental. Hundreds of photocatalysts have recently been discovered for various chemical reactions, such as water splitting and carbon dioxide reduction, employing these databases and/or data informatics, machine learning, and high-throughput computational and experimental methods. In this article, we review these data-driven photocatalyst discoveries, emphasizing the methods and techniques developed in the last few years to determine the (photo)electrochemical stability of photocatalysts, leading to the discovery of photocatalysts that remain robust and durable under operational conditions. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Data-Driven Discovery of Robust Materials for Photocatalytic Energy Conversion","authors":"Arunima K. Singh, R. Gorelik, T. Biswas","doi":"10.1146/annurev-conmatphys-031620-100957","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-031620-100957","url":null,"abstract":"The solar–to–chemical energy conversion of Earth-abundant resources like water or greenhouse gas pollutants like CO2 promises an alternate energy source that is clean, renewable, and environmentally friendly. The eventual large-scale application of such photo-based energy conversion devices can be realized through the discovery of novel photocatalytic materials that are efficient, selective, and robust. In the past decade, the Materials Genome Initiative has led to a major leap in the development of materials databases, both computational and experimental. Hundreds of photocatalysts have recently been discovered for various chemical reactions, such as water splitting and carbon dioxide reduction, employing these databases and/or data informatics, machine learning, and high-throughput computational and experimental methods. In this article, we review these data-driven photocatalyst discoveries, emphasizing the methods and techniques developed in the last few years to determine the (photo)electrochemical stability of photocatalysts, leading to the discovery of photocatalysts that remain robust and durable under operational conditions. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47792488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-20DOI: 10.1146/annurev-conmatphys-040821-115500
A. Zöttl, H. Stark
Active colloids are self-propelled particles moving in viscous fluids by consuming fuel from their surroundings. Here, we review the numerical and theoretical modeling of active colloids propelled by self-generated near-surface flows. We start with the generic model of an active Brownian particle taking into account potential forces and effective pairwise interaction, which include hydrodynamic and phoretic interactions. Also, the squirmer as a model microswimmer is introduced. We then discuss the explicit modeling of self-generated fluid flow and the full hydrodynamic-chemical coupling. Finally, we discuss recent advances in selected topics in which modeling of active colloids is used to study motion in crowded and complex environments, microrheology in active baths, active colloidal engines, adaptive responses of active colloids with the help of machine learning techniques, as well as effects of colloid and fluid inertia. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Modeling Active Colloids: From Active Brownian Particles to Hydrodynamic and Chemical Fields","authors":"A. Zöttl, H. Stark","doi":"10.1146/annurev-conmatphys-040821-115500","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040821-115500","url":null,"abstract":"Active colloids are self-propelled particles moving in viscous fluids by consuming fuel from their surroundings. Here, we review the numerical and theoretical modeling of active colloids propelled by self-generated near-surface flows. We start with the generic model of an active Brownian particle taking into account potential forces and effective pairwise interaction, which include hydrodynamic and phoretic interactions. Also, the squirmer as a model microswimmer is introduced. We then discuss the explicit modeling of self-generated fluid flow and the full hydrodynamic-chemical coupling. Finally, we discuss recent advances in selected topics in which modeling of active colloids is used to study motion in crowded and complex environments, microrheology in active baths, active colloidal engines, adaptive responses of active colloids with the help of machine learning techniques, as well as effects of colloid and fluid inertia. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43106249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-21DOI: 10.1146/annurev-conmatphys-040721-023358
A. Libchaber
The overall effect of temperature gradients is stressed for the Earth's core and surface, but also for the Sun's surface. Using Rayleigh–Bénard convection in helium and mercury, we measured all of the scaling properties of the period-doubling cascade and quasiperiodicity. Hard turbulence scaling properties are presented in an experiment using helium gas at low temperature. A 2/7 scaling law is measured and also an exponential distribution for temperature fluctuations is observed. We present a study of a Rayleigh–Bénard convection cell with an open top and a floater. One of the simplest limit cycles is observed for the floater position. It follows a model proposed by Wilson for continents motion. Using the Soret effect, we study how temperature differences lead to strong accumulation of DNA suspensions. Also using polyethylene glycol concentration gradients, we measured local DNA and RNA accumulation. Finally, using thermal convection, we build one of the smallest PCR machines. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"A Journey Through Nonlinear Dynamics: The Case of Temperature Gradients","authors":"A. Libchaber","doi":"10.1146/annurev-conmatphys-040721-023358","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040721-023358","url":null,"abstract":"The overall effect of temperature gradients is stressed for the Earth's core and surface, but also for the Sun's surface. Using Rayleigh–Bénard convection in helium and mercury, we measured all of the scaling properties of the period-doubling cascade and quasiperiodicity. Hard turbulence scaling properties are presented in an experiment using helium gas at low temperature. A 2/7 scaling law is measured and also an exponential distribution for temperature fluctuations is observed. We present a study of a Rayleigh–Bénard convection cell with an open top and a floater. One of the simplest limit cycles is observed for the floater position. It follows a model proposed by Wilson for continents motion. Using the Soret effect, we study how temperature differences lead to strong accumulation of DNA suspensions. Also using polyethylene glycol concentration gradients, we measured local DNA and RNA accumulation. Finally, using thermal convection, we build one of the smallest PCR machines. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41754467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-06DOI: 10.1146/annurev-conmatphys-040821-112149
S. Spagnolie, Patrick T. Underhill
We review the literature on swimming in complex fluids. A classification is proposed by comparing the length and timescales of a swimmer with those of nearby obstacles, interpreted broadly, extending from rigid or soft confining boundaries to molecules that confer the bulk fluid with complex stresses. A third dimension in the classification is the concentration of swimmers, which incorporates fluids whose complexity arises purely by the collective motion of swimming organisms. For each of the eight system classes that we identify, we provide a background and describe modern research findings. Although some classes have seen a great deal of attention for decades, others remain uncharted waters still open and awaiting exploration. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Swimming in Complex Fluids","authors":"S. Spagnolie, Patrick T. Underhill","doi":"10.1146/annurev-conmatphys-040821-112149","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040821-112149","url":null,"abstract":"We review the literature on swimming in complex fluids. A classification is proposed by comparing the length and timescales of a swimmer with those of nearby obstacles, interpreted broadly, extending from rigid or soft confining boundaries to molecules that confer the bulk fluid with complex stresses. A third dimension in the classification is the concentration of swimmers, which incorporates fluids whose complexity arises purely by the collective motion of swimming organisms. For each of the eight system classes that we identify, we provide a background and describe modern research findings. Although some classes have seen a great deal of attention for decades, others remain uncharted waters still open and awaiting exploration. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43533125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-29DOI: 10.1146/annurev-conmatphys-031720-030658
M. Fisher, V. Khemani, A. Nahum, S. Vijay
Quantum circuits—built from local unitary gates and local measurements—are a new playground for quantum many-body physics and a tractable setting to explore universal collective phenomena far from equilibrium. These models have shed light on longstanding questions about thermalization and chaos, and on the underlying universal dynamics of quantum information and entanglement. In addition, such models generate new sets of questions and give rise to phenomena with no traditional analog, such as dynamical phase transitions in quantum systems that are monitored by an external observer. Quantum circuit dynamics is also topical in view of experimental progress in building digital quantum simulators that allow control of precisely these ingredients. Randomness in the circuit elements allows a high level of theoretical control, with a key theme being mappings between real-time quantum dynamics and effective classical lattice models or dynamical processes. Many of the universal phenomena that can be identified in this tractable setting apply to much wider classes of more structured many-body dynamics. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Random Quantum Circuits","authors":"M. Fisher, V. Khemani, A. Nahum, S. Vijay","doi":"10.1146/annurev-conmatphys-031720-030658","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-031720-030658","url":null,"abstract":"Quantum circuits—built from local unitary gates and local measurements—are a new playground for quantum many-body physics and a tractable setting to explore universal collective phenomena far from equilibrium. These models have shed light on longstanding questions about thermalization and chaos, and on the underlying universal dynamics of quantum information and entanglement. In addition, such models generate new sets of questions and give rise to phenomena with no traditional analog, such as dynamical phase transitions in quantum systems that are monitored by an external observer. Quantum circuit dynamics is also topical in view of experimental progress in building digital quantum simulators that allow control of precisely these ingredients. Randomness in the circuit elements allows a high level of theoretical control, with a key theme being mappings between real-time quantum dynamics and effective classical lattice models or dynamical processes. Many of the universal phenomena that can be identified in this tractable setting apply to much wider classes of more structured many-body dynamics. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47810336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-01DOI: 10.1146/annurev-conmatphys-040821-125506
Michel Fruchart, C. Scheibner, V. Vitelli
Elasticity typically refers to a material's ability to store energy, whereas viscosity refers to a material's tendency to dissipate it. In this review, we discuss fluids and solids for which this is not the case. These materials display additional linear response coefficients known as odd viscosity and odd elasticity. We first introduce odd viscosity and odd elasticity from a continuum perspective, with an emphasis on their rich phenomenology, including transverse responses, modified dislocation dynamics, and topological waves. We then provide an overview of systems that display odd viscosity and odd elasticity. These systems range from quantum fluids and astrophysical gases to active and driven matter. Finally, we comment on microscopic mechanisms by which odd viscosity and odd elasticity arise.
{"title":"Odd Viscosity and Odd Elasticity","authors":"Michel Fruchart, C. Scheibner, V. Vitelli","doi":"10.1146/annurev-conmatphys-040821-125506","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040821-125506","url":null,"abstract":"Elasticity typically refers to a material's ability to store energy, whereas viscosity refers to a material's tendency to dissipate it. In this review, we discuss fluids and solids for which this is not the case. These materials display additional linear response coefficients known as odd viscosity and odd elasticity. We first introduce odd viscosity and odd elasticity from a continuum perspective, with an emphasis on their rich phenomenology, including transverse responses, modified dislocation dynamics, and topological waves. We then provide an overview of systems that display odd viscosity and odd elasticity. These systems range from quantum fluids and astrophysical gases to active and driven matter. Finally, we comment on microscopic mechanisms by which odd viscosity and odd elasticity arise.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44345505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-23DOI: 10.1146/annurev-conmatphys-031620-101617
A. Chandran, Thomas Iadecola, V. Khemani, R. Moessner
Weakly interacting quasiparticles play a central role in the low-energy description of many phases of quantum matter. At higher energies, however, quasiparticles cease to be well defined in generic many-body systems owing to a proliferation of decay channels. In this review, we discuss the phenomenon of quantum many-body scars, which can give rise to certain species of stable quasiparticles throughout the energy spectrum. This goes along with a set of unusual nonequilibrium phenomena including many-body revivals and nonthermal stationary states. We provide a pedagogical exposition of this physics via a simple yet comprehensive example, that of a spin-1 XY model. We place our discussion in the broader context of symmetry-based constructions of many-body scar states, projector embeddings, and Hilbert space fragmentation. We conclude with a summary of experimental progress and theoretical puzzles. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Quantum Many-Body Scars: A Quasiparticle Perspective","authors":"A. Chandran, Thomas Iadecola, V. Khemani, R. Moessner","doi":"10.1146/annurev-conmatphys-031620-101617","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-031620-101617","url":null,"abstract":"Weakly interacting quasiparticles play a central role in the low-energy description of many phases of quantum matter. At higher energies, however, quasiparticles cease to be well defined in generic many-body systems owing to a proliferation of decay channels. In this review, we discuss the phenomenon of quantum many-body scars, which can give rise to certain species of stable quasiparticles throughout the energy spectrum. This goes along with a set of unusual nonequilibrium phenomena including many-body revivals and nonthermal stationary states. We provide a pedagogical exposition of this physics via a simple yet comprehensive example, that of a spin-1 XY model. We place our discussion in the broader context of symmetry-based constructions of many-body scar states, projector embeddings, and Hilbert space fragmentation. We conclude with a summary of experimental progress and theoretical puzzles. Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 14 is March 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46040717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-13DOI: 10.1146/annurev-conmatphys-040821-113439
M. Stern, A. Murugan
Learning is traditionally studied in biological or computational systems. The power of learning frameworks in solving hard inverse problems provides an appealing case for the development of physical learning in which physical systems adopt desirable properties on their own without computational design. It was recently realized that large classes of physical systems can physically learn through local learning rules, autonomously adapting their parameters in response to observed examples of use. We review recent work in the emerging field of physical learning, describing theoretical and experimental advances in areas ranging from molecular self-assembly to flow networks and mechanical materials. Physical learning machines provide multiple practical advantages over computer designed ones, in particular by not requiring an accurate model of the system, and their ability to autonomously adapt to changing needs over time. As theoretical constructs, physical learning machines afford a novel perspective on how physical constraints modify abstract learning theory.
{"title":"Learning Without Neurons in Physical Systems","authors":"M. Stern, A. Murugan","doi":"10.1146/annurev-conmatphys-040821-113439","DOIUrl":"https://doi.org/10.1146/annurev-conmatphys-040821-113439","url":null,"abstract":"Learning is traditionally studied in biological or computational systems. The power of learning frameworks in solving hard inverse problems provides an appealing case for the development of physical learning in which physical systems adopt desirable properties on their own without computational design. It was recently realized that large classes of physical systems can physically learn through local learning rules, autonomously adapting their parameters in response to observed examples of use. We review recent work in the emerging field of physical learning, describing theoretical and experimental advances in areas ranging from molecular self-assembly to flow networks and mechanical materials. Physical learning machines provide multiple practical advantages over computer designed ones, in particular by not requiring an accurate model of the system, and their ability to autonomously adapt to changing needs over time. As theoretical constructs, physical learning machines afford a novel perspective on how physical constraints modify abstract learning theory.","PeriodicalId":7925,"journal":{"name":"Annual Review of Condensed Matter Physics","volume":null,"pages":null},"PeriodicalIF":22.6,"publicationDate":"2022-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42166241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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