Review of Measurement-Induced Dynamic Quantum Phase Transitions

A new class of phase transitions has been recently studied in quantum many-body systems that are subject to measurements but not otherwise open to any external decoherence.  This phase transition arises from a competition between scrambling dynamics that produces entanglement and hides quantum information from the measurements, and the measurements which generally reduce entanglement and reveal or “collapse” quantum information.  In the “ordered” phase, the scrambling wins and the system is able to encode and store a nonzero density of quantum information and is volume-law entangled.  The phase transitions in 1+1 dimensions are apparently new types of nonunitary CFTs with zero central charge.  The upper critical dimension and mean-field theory are still unclear.