Growth of entanglement entropy under local projective measurements

Nonequilibrium dynamics of many-body quantum systems under the effect of measurement protocols is attracting an increasing amount of attention. It has been recently revealed that measurements may induce an abrupt change in the scaling law of the bipartite entanglement entropy, thus suggesting the existence of different nonequilibrium regimes. However, our understanding of how these regimes appear and whether they survive in the thermodynamic limit is much less established. Here we investigate these questions on a one-dimensional quadratic fermionic model: this allows us to reach system sizes relevant in the thermodynamic sense. We show that local projective measurements induce a qualitative modification of the time growth of the entanglement entropy which changes from linear to logarithmic. However, in the stationary regime, the logarithmic behavior of the entanglement entropy does not survive in the thermodynamic limit and, for any finite value of the measurement rate, we numerically show the existence of a single area-law phase for the entanglement entropy. Finally, exploiting the quasiparticle picture, we further support our results by analyzing the fluctuations of the stationary entanglement entropy and its scaling behavior.

Automated summary

The nonequilibrium dynamics of quantum systems under measurement protocols has attracted attention due to its impact on the scaling law of bipartite entanglement entropy. However, it is still unclear how these different nonequilibrium regimes appear and whether they persist in the thermodynamic limit. In this study, a one-dimensional quadratic fermionic model is used to investigate these questions, revealing a qualitative modification of the time growth of the entanglement entropy induced by local projective measurements. Nevertheless, in the thermodynamic limit, the logarithmic behavior of the entanglement entropy in the stationary regime does not survive, and a single area-law phase is identified for any finite value of the measurement rate.