Interferometric Order Parameter for Excited-State Quantum Phase Transitions in Bose-Einstein Condensates

Excited-state quantum phase transitions extend the notion of quantum phase transitions beyond the ground state. They are characterized by closing energy gaps amid the spectrum. Identifying order parameters for excited-state quantum phase transitions poses, however, a major challenge. We introduce a topological order parameter that distinguishes excited-state phases in a large class of mean-field models and can be accessed by interferometry in current experiments with spinor Bose-Einstein condensates. Our work opens a way for the experimental characterization of excited-state quantum phases in atomic many-body systems.

Automated summary

Excited-state quantum phase transitions extend the concept of quantum phase transitions beyond the ground state, characterized by closing energy gaps in the spectrum. Identifying order parameters for excited-state quantum phase transitions is a challenge, but introducing a topological order parameter distinguishes excited state phases in experiments with spinor Bose-Einstein condensates, providing a way to experimentally characterize excited-state quantum phases in atomic many-body systems.