Observation of Critical Phenomena in Parity-Time-Symmetric Quantum Dynamics

TLDR

The study aims to experimentally simulate nonunitary quantum dynamics in a PT‑symmetric non‑Hermitian system and investigate the information flow between the system and its environment. This is achieved using a single‑photon interferometric network that implements the PT‑symmetric dynamics and allows measurement of quantum‑state distinguishability. The experiment reveals oscillatory distinguishability and complete information retrieval in the PT‑unbroken regime, demonstrates power‑law critical behavior of distinguishability and recurrence time near the exceptional point, shows dependence on symmetry and initial conditions, and confirms that a finite‑dimensional entanglement partner in the environment drives the retrieval, constituting the first experimental characterization of critical phenomena in PT‑symmetric nonunitary quantum dynamics.

Abstract

We experimentally simulate nonunitary quantum dynamics using a single-photon interferometric network and study the information flow between a parity-time- (PT-)symmetric non-Hermitian system and its environment. We observe oscillations of quantum-state distinguishability and complete information retrieval in the PT-symmetry-unbroken regime. We then characterize in detail critical phenomena of the information flow near the exceptional point separating the PT-unbroken and PT-broken regimes, and demonstrate power-law behavior in key quantities such as the distinguishability and the recurrence time. We also reveal how the critical phenomena are affected by symmetry and initial conditions. Finally, introducing an ancilla as an environment and probing quantum entanglement between the system and the environment, we confirm that the observed information retrieval is induced by a finite-dimensional entanglement partner in the environment. Our work constitutes the first experimental characterization of critical phenomena in PT-symmetric nonunitary quantum dynamics.