Transitions in the Learnability of Global Charges from Local Measurements

Fergus Barratt, Utkarsh Agrawal, Andrew C. Potter, Sarang Gopalakrishnan, Romain Vasseur

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


We consider monitored quantum systems with a global conserved charge, and ask how efficiently an observer ("eavesdropper") can learn the global charge of such systems from local projective measurements. We find phase transitions as a function of the measurement rate, depending on how much information about the quantum dynamics the eavesdropper has access to. For random unitary circuits with U(1) symmetry, we present an optimal classical classifier to reconstruct the global charge from local measurement outcomes only. We demonstrate the existence of phase transitions in the performance of this classifier in the thermodynamic limit. We also study numerically improved classifiers by including some knowledge about the unitary gates pattern.

Original languageEnglish (US)
Article number200602
JournalPhysical review letters
Issue number20
StatePublished - Nov 11 2022
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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