Robust Oscillations and Edge Modes in Nonunitary Floquet Systems

TL;DR

This paper investigates how weak measurements induce a transition to an oscillatory phase in nonunitary Floquet spin chains, revealing robust edge modes and a complex spectrum that are stable against interactions and disorder.

Contribution

It introduces a novel phase transition driven by measurement strength in nonunitary Floquet systems and links it to edge modes and spectral properties.

Findings

Transition to oscillatory phase with increased measurement strength

Existence of a robust, real edge π-mode in the oscillatory phase

Oscillations are stable against interactions and disorder

Abstract

We explore oscillatory behaviour in a family of periodically driven spin chains which are subject to a weak measurement followed by post-selection. We discover a transition to an oscillatory phase as the strength of the measurement is increased. By mapping these spin chains to free fermion models, we find that this transition is reflected in the opening of a gap in the imaginary direction. Interestingly, we find a robust, purely real, edge $\pi$-mode in the oscillatory phase. We establish a correspondence between the complex bulk spectrum and these edge modes. These oscillations are numerically found to be stable against interactions and disorder.