Measurement-enhanced entanglement in a monitored superconducting chain

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.

5 pages of main text (4 figures) and 9 pages of supplemental material (2 figures); companion paper to arXiv:2607.07835. Comments are welcome

Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Superconductivity (cond-mat.supr-con)

arXiv:2604.04375 [quant-ph]

(or arXiv:2604.04375v2 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2604.04375 Focus to learn more arXiv-issued DOI via DataCite

arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website.

Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them.

Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs.