Experimental Observation of Dynamical Phase Transitions in a Dephased Photonic Quantum Walk.

Authors

Xiaojian Huang, Lei Xiao, Bingzi Huo, Xiaowei Wang, Stefano Longhi, Peng Xue

Published in

Physical review letters. Volume 137. Issue 11. Pages 110804. Sep 11, 2026.

Abstract

Dynamical phase transitions in open quantum systems govern how nonequilibrium states relax toward a stationary state. We study these transitions experimentally using a discrete-time photonic quantum walk on a three-node graph. A tunable synthetic gauge flux and calibrated dephasing allow us to control time-reversal symmetry and the detailed balance properties of the effective Markovian dynamics. With detailed balance, we observe a first-order dynamical phase transition marked by a crossing of real Liouvillian eigenvalues. When detailed balance is broken, we observe a second-order dynamical phase transition at an exceptional point where eigenvalues and eigenvectors coalesce. By progressively reducing the dephasing strength, we track the crossover toward the quantum-coherent regime and determine that the transitions persist down to a finite threshold. Our results establish a controllable platform for the experimental investigation of a class of relaxation dynamical phase transitions governed by detailed balance and exceptional points, linking Liouvillian spectral topology to relaxation criticality.

PMID:
42789877
Bibliographic data and abstract were imported from PubMed on 26 Sep 2026.

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