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

• URL: http://arxiv.org/abs/2606.15935v1
• Date: Sun, 14 Jun 2026 17:26:15 GMT
• Title: Experimental Observation of Dynamical Phase Transitions in a Dephased Photonic Quantum Walk
• Abstract summary: Dynamical phase transitions in open quantum systems govern how non-equilibrium states relax toward a stationary state.<n>We study these transitions experimentally using a discrete-time photonic quantum walk on a three-node graph.<n>Our results link Liouvillian spectral topology to relaxation criticality and demonstrate a controllable platform for engineered dissipative dynamics.
• Score: 12.497539919158582
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Dynamical phase transitions in open quantum systems govern how non-equilibrium 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 link Liouvillian spectral topology to relaxation criticality and demonstrate a controllable platform for engineered dissipative dynamics.

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