{"title":"Measurement-Induced Phases of Matter Require Feedback","authors":"Aaron J. Friedman, Oliver Hart, Rahul Nandkishore","doi":"10.1103/prxquantum.4.040309","DOIUrl":null,"url":null,"abstract":"We explore universality and phases of matter in hybrid quantum dynamics combining chaotic time evolution and projective measurements. We develop a unitary representation of measurements based on the Stinespring theorem, which we crucially identify with the time evolution of the system and measurement apparatus, affording significant technical advantages and conceptual insight into hybrid dynamics. We diagnose spectral properties in the presence of measurements for the first time, along with standard, experimentally tractable probes of phase structure, finding no nontrivial effects due to measurements in the absence of feedback. We also establish that nonlinearity in the density matrix is neither sufficient nor necessary to see a transition, and instead identify utilization of the measurement outcomes (i.e., “feedback”) as the crucial ingredient. After reviewing the definition of a phase of matter, we identify nontrivial orders in adaptive hybrid dynamics—in which measurement outcomes determine future unitary gates—finding a genuine measurement-induced absorbing-state phase transition in an adaptive quantum East model. In general, we find that only deterministic and constrained Haar-random dynamics with active feedback and without continuous symmetries can realize genuine, measurement-induced phases of matter.2 MoreReceived 31 October 2022Revised 28 May 2023Accepted 18 September 2023DOI:https://doi.org/10.1103/PRXQuantum.4.040309Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDynamical phase transitionsNonequilibrium statistical mechanicsQuantum chaosQuantum entanglementQuantum feedbackQuantum measurementsPhysical Systems1-dimensional spin chainsFloquet systemsQuantum spin modelsTechniquesQuantum spin chainsAtomic, Molecular & OpticalCondensed Matter, Materials & Applied PhysicsQuantum Information, Science & TechnologyStatistical Physics & Thermodynamics","PeriodicalId":74587,"journal":{"name":"PRX quantum : a Physical Review journal","volume":"63 1","pages":"0"},"PeriodicalIF":11.0000,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"PRX quantum : a Physical Review journal","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1103/prxquantum.4.040309","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"PHYSICS, APPLIED","Score":null,"Total":0}
引用次数: 2
Abstract
We explore universality and phases of matter in hybrid quantum dynamics combining chaotic time evolution and projective measurements. We develop a unitary representation of measurements based on the Stinespring theorem, which we crucially identify with the time evolution of the system and measurement apparatus, affording significant technical advantages and conceptual insight into hybrid dynamics. We diagnose spectral properties in the presence of measurements for the first time, along with standard, experimentally tractable probes of phase structure, finding no nontrivial effects due to measurements in the absence of feedback. We also establish that nonlinearity in the density matrix is neither sufficient nor necessary to see a transition, and instead identify utilization of the measurement outcomes (i.e., “feedback”) as the crucial ingredient. After reviewing the definition of a phase of matter, we identify nontrivial orders in adaptive hybrid dynamics—in which measurement outcomes determine future unitary gates—finding a genuine measurement-induced absorbing-state phase transition in an adaptive quantum East model. In general, we find that only deterministic and constrained Haar-random dynamics with active feedback and without continuous symmetries can realize genuine, measurement-induced phases of matter.2 MoreReceived 31 October 2022Revised 28 May 2023Accepted 18 September 2023DOI:https://doi.org/10.1103/PRXQuantum.4.040309Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDynamical phase transitionsNonequilibrium statistical mechanicsQuantum chaosQuantum entanglementQuantum feedbackQuantum measurementsPhysical Systems1-dimensional spin chainsFloquet systemsQuantum spin modelsTechniquesQuantum spin chainsAtomic, Molecular & OpticalCondensed Matter, Materials & Applied PhysicsQuantum Information, Science & TechnologyStatistical Physics & Thermodynamics