Dresden 2026 – scientific programme

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QI: Fachverband Quanteninformation

QI 21: Quantum Information: Concepts and Methods III

QI 21.6: Talk

Friday, March 13, 2026, 11:30–11:45, BEY/0245

Measurement-induced transitions in fermionic systems — •Ihor Poboiko, Igor Gornyi, and Alexander D. Mirlin — Karlsruhe Institute of Technology, Karlsruhe, Germany

We develop a theory of measurement-induced phase transitions (MIPT) for d-dimensional lattice free fermions subject to random projective measurements of local site occupation numbers. In the limit of rare measurements, γ ≪ J (where γ is measurement rate per site and J is hopping constant), we derive a non-linear sigma model (NLSM) as an effective field theory of the problem. On the Gaussian level, valid in the limit γ/J → 0, this model predicts "critical" (i.e. logarithmic enhancement of area law) behavior for the entanglement entropy. However, one-loop renormalization group analysis shows that for d=1, the logarithmic growth saturates at a finite value (J / γ)² even for rare measurements, implying existence of a single area-law phase. The crossover between logarithmic growth and saturation, however, happens at an exponentially large scale, ln(l_corr) ∼ J/γ, thus making it easy to confuse with a transition in a finite-size system. Furthermore, utilizing ε-expansion, we demonstrate that the "critical" phase is stabilized for d>1 with a transition to the area-law phase at a finite value of γ / J. The analytical calculations are supported by and are in excellent agreement with the extensive numerical simulations for d=1,2.

Keywords: measurement-induced transitions; quantum entanglement; non-linear sigma-model