Rahul Nandkishore
University of Colorado, Boulder

Siddharth Ashok Parameswaran
University of California, Irvine



Project Title

Transitions to Ergodicity: Emergence of Observers in Many-Body Quantum Systems

Project Summary

Observers play a crucial role in the traditional \`Copenhagen’ interpretation of quantum mechanics, in that isolated quantum systems can exist in superposition states (cats both alive and dead) but observed quantum systems are always in a definite state (cats either alive or dead). How can this understanding be extended to incorporate fully quantum observers? New advances in the statistical mechanics of isolated quantum many body systems are providing the answer, which revolves around the structure of quantum entanglement. It emerges that isolated quantum systems can exist in dynamical phases with an 'internal observer' (thermalization) and also in phases without an \`internal observer’ (many body localization), with the dynamical transition between these regimes being associated with the birth of an internal fully quantum observer. We propose to explore the implications of these emerging paradigms for diverse fields, ranging from quantum chaos to holography and black hole physics to quantum biology, with a view to understanding the role of the observer in each field, and on using this understanding to gain new insights into fundamental problems in each discipline.



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