Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 41: Quantum Dynamics, Decoherence, and Quantum Information (joint session DY/TT)

DY 41.1: Talk

Friday, March 21, 2025, 09:30–09:45, H37

Entanglement phase transitions in unitary circuit games with free fermions — •Raúl Morral-Yepes^1,2, Marc Langer^1,2, Adam Smith^3,4, Barbara Kraus^1,2, and Frank Pollmann^1,2 — ¹Technical University of Munich, TUM School of Natural Sciences — ²Munich Center for Quantum Science and Technology (MCQST) — ³School of Physics and Astronomy, University of Nottingham — ⁴Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems

In the recently introduced framework of unitary circuit games, two competing parties an entangler and a disentangler can induce an entanglement phase transition, distinct from measurement-induced transitions. In this work, we study such games within the context of matchgate dynamics, which correspond to free fermion systems. First, we investigate the entanglement properties of fermionic Gaussian states (FGS) and explore different methods for their disentangling. We propose a representation of FGS using a minimal matchgate circuit in a standard form, and introduce algorithms for updating this representation as unitary operations are applied. Within this framework, we define a natural disentangling procedure that reduces the number of gates in the circuit, thereby decreasing the system's entanglement. We then analyze the unitary game using this gate disentangler, observing a phase transition between a volume-law and area-law entanglement phase. The nature of this transition differs depending on whether we examine Rényi-0 or other entanglement entropies.

Keywords: entanglement; free fermions; matchgates; phase transitions; circuits