SciPost Physics

SciPost Phys. 12, 009 (2022) · published 7 January 2022

• doi: 10.21468/SciPostPhys.12.1.009
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Abstract

Hybrid evolution protocols, composed of unitary dynamics and repeated, weak or projective measurements, give rise to new, intriguing quantum phenomena, including entanglement phase transitions and unconventional conformal invariance. Defying the complications imposed by the non-linear and stochastic nature of the measurement process, we introduce a scenario of measurement-induced many body evolution, which possesses an exact analytical solution: bosonic Gaussian measurements. The evolution features a competition between the continuous observation of linear boson operators and a free Hamiltonian, and it is characterized by a unique and exactly solvable covariance matrix. Within this framework, we then consider an elementary model for quantum criticality, the free boson conformal field theory, and investigate in which way criticality is modified under measurements. Depending on the measurement protocol, we distinguish three fundamental scenarios (a) enriched quantum criticality, characterized by a logarithmic entanglement growth with a floating prefactor, or the loss of criticality, indicated by an entanglement growth with either (b) an area-law or (c) a volume-law. For each scenario, we discuss the impact of imperfect measurements, which reduce the purity of the wavefunction and are equivalent to Markovian decoherence, and present a set of observables, e.g., real-space correlations, the relaxation time, and the entanglement structure, to classify the measurement-induced dynamics for both pure and mixed states. Finally, we present an experimental tomography scheme, which grants access to the density operator of the system by using the continuous measurement record only.

• Sierant et al., Measurement-induced phase transitions in (d+1) -dimensional stabilizer circuits
  Phys. Rev. B 106, 214316 (2022) [Crossref]
• Kells et al., Topological transitions in weakly monitored free fermions
  SciPost Phys. 14, 031 (2023) [Crossref]
• Xing et al., Interactions and integrability in weakly monitored Hamiltonian systems
  Phys. Rev. B 109, L060302 (2024) [Crossref]
• Ladewig et al., Monitored open fermion dynamics: Exploring the interplay of measurement, decoherence, and free Hamiltonian evolution
  Phys. Rev. Research 4, 033001 (2022) [Crossref]
• Doggen et al., Evolution of many-body systems under ancilla quantum measurements
  Phys. Rev. B 107, 214203 (2023) [Crossref]
• Klocke et al., Majorana Loop Models for Measurement-Only Quantum Circuits
  Phys. Rev. X 13, 041028 (2023) [Crossref]
• Li et al., Decodable hybrid dynamics of open quantum systems with Z2 symmetry
  Phys. Rev. B 108, 214302 (2023) [Crossref]
• Turkeshi, Measurement-induced criticality as a data-structure transition
  Phys. Rev. B 106, 144313 (2022) [Crossref]
• Altland et al., Dynamics of measured many-body quantum chaotic systems
  Phys. Rev. Research 4, L022066 (2022) [Crossref]
• Carollo et al., Entangled multiplets and spreading of quantum correlations in a continuously monitored tight-binding chain
  Phys. Rev. B 106, L220304 (2022) [Crossref]
• Dias et al., Quantum noise as a symmetry-breaking field
  Phys. Rev. B 108, L060302 (2023) [Crossref]
• Khor et al., Measurement-induced chirality: Diffusion and disorder
  Phys. Rev. B 108, 214305 (2023) [Crossref]
• Lee et al., Entanglement Phase Transition Due to Reciprocity Breaking without Measurement or Postselection
  PRX Quantum 5, 010313 (2024) [Crossref]
• Pöpperl et al., Measurements on an Anderson chain
  Phys. Rev. B 107, 174203 (2023) [Crossref]
• Sierant et al., Controlling Entanglement at Absorbing State Phase Transitions in Random Circuits
  Phys. Rev. Lett. 130, 120402 (2023) [Crossref]
• Szyniszewski et al., Disordered monitored free fermions
  Phys. Rev. B 108, 165126 (2023) [Crossref]
• Sharma et al., Measurement-induced criticality in extended and long-range unitary circuits
  SciPost Phys. Core 5, 023 (2022) [Crossref]
• Lóio et al., Purification timescales in monitored fermions
  Phys. Rev. B 108, L020306 (2023) [Crossref]
• Lami et al., Continuously monitored quantum systems beyond Lindblad dynamics
  New J. Phys. 26, 023041 (2024) [Crossref]
• Garratt et al., Measurements Conspire Nonlocally to Restructure Critical Quantum States
  Phys. Rev. X 13, 021026 (2023) [Crossref]
• Klocke et al., Topological order and entanglement dynamics in the measurement-only XZZX quantum code
  Phys. Rev. B 106, 104307 (2022) [Crossref]