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arXiv · 2604.04375

Measurement-enhanced entanglement in a monitored superconducting chain

Rui-Jing Guo·Ji-Yao Chen·Zhi-Yuan Wei
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Abstract

A common view in monitored quantum dynamics is that local measurements suppress entanglement growth. We show that this intuition can fail in a one-dimensional spinful fermionic chain governed by a BCS Hamiltonian with pairing strength $\Delta$ and subject to continuous, on-site, spin-resolved charge measurements at rate $\gamma$. Using free-fermion simulations and quasiparticle analysis, we show that pairing suppresses entanglement growth, while measurements suppress pairing. Their competition yields measurement-enhanced entanglement: for $\Delta>0$, the steady-state entanglement $\mathcal{S}_s$ increases with $\gamma$ over a finite interval $0<\gamma<\gamma_{\mathrm{peak}}$. This occurs because stronger measurements suppress pairing correlations, which would otherwise suppress entanglement growth. Using a nonlinear sigma-model calculation and free-fermion simulations, we provide evidence that for $\Delta>0$ and small but finite $\gamma$, the steady-state entanglement scales as $\mathcal{S}_s(L)\sim \ln^2 L$. This implies that, in this setting, measurement-enhanced entanglement does not persist in the thermodynamic limit.

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Rui-Jing Guo, Ji-Yao Chen, Zhi-Yuan Wei. 2026-04-06. Measurement-enhanced entanglement in a monitored superconducting chain. https://arxiv.org/abs/2604.04375

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