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arXiv:2602.12340 · Physical review. B./Physical review. B

Controlled Zeno-Induced Localization of Free Fermions in a Quasiperiodic Chain

Pinaki Singha, Nilanjan Roy, Marcin Szyniszewski, Auditya Sharma

cond-mat.stat-mechcond-mat.dis-nnquant-phSubmitted Feb 12, 2026• Announced Feb 16, 2026• 0 citations• Revised May 11, 2026 (v2)
v1 · Feb 12, 2026v2 · May 11, 2026
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Abstract

We investigate measurement-induced localization in a continuously monitored one-dimensional Aubry--André--Harper model, focusing on the quantum Zeno regime in which the measurements dominate coherent dynamics. The presence of a quasiperiodic potential renders the problem analytically tractable and enables a controlled study of the interplay between monitoring and disorder. We develop an analytical description based on an instantaneous Schrödinger equation with a measurement-induced effective potential constructed self-consistently from individual quantum trajectories, without relying on postselection. In the quantum Zeno regime, an emergent dominant energy scale reduces the problem to a transfer-matrix formulation of an effective non-Hermitian Hamiltonian, which allows direct computation of the Lyapunov exponent. Complementarily, we extract the localization length numerically from long-time steady-state quantum state diffusion trajectories by reconstructing the intrinsic localized single-particle wave functions and analyzing their spatial decay. These numerical results show quantitative agreement with the effective theory predictions, with controlled corrections of order $J^2/[λ^2+(γ/2)^2]$ (where $J$ is the hopping amplitude, $γ$ the measurement strength, and $λ$ the quasiperiodic potential). Our results underscore the connection between the effective non-Hermitian description and the stochastic monitored dynamics, showing the interplay between Zeno-like localization, coherent hopping, and quasiperiodic-disorder-induced localization, while also laying the groundwork for understanding and exploiting measurement-induced localization as a tool for quantum control and state preparation.

Journal reference
Phys. Rev. B 113, 235122 (2026)
DOI
10.1103/27g7-tvqh
Comments
19 pages, 5 figures, 1 table

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We investigate measurement-induced localization in a continuously monitored one-dimensional Aubry--André--Harper model, focusing on the quantum Zeno regime in which the measurements dominate coherent dynamics. The presence of a quasiperiodic potential renders the problem analytically tractable and enables a controlled study of the interplay between monitoring and disorder. We develop an analytical description based on an instantaneous Schrödinger equation with a measurement-induced effective potential constructed self-consistently from individual quantum trajectories, without relying on postselection. In the quantum Zeno regime, an emergent dominant energy scale reduces the problem to a transfer-matrix formulation of an effective non-Hermitian Hamiltonian, which allows direct computation of the Lyapunov exponent. Complementarily, we extract the localization length numerically from long-time steady-state quantum state diffusion trajectories by reconstructing the intrinsic localized single-particle wave functions and analyzing their spatial decay. These numerical results show quantitative agreement with the effective theory predictions, with controlled corrections of order J2/[λ2+(γ/2)2]J^2/[λ^2+(γ/2)^2]J2/[λ2+(γ/2)2] (where JJJ is the hopping amplitude, γγγ the measurement strength, and λλλ the quasiperiodic potential). Our results underscore the connection between the effective non-Hermitian description and the stochastic monitored dynamics, showing the interplay between Zeno-like localization, coherent hopping, and quasiperiodic-disorder-induced localization, while also laying the groundwork for understanding and exploiting measurement-induced localization as a tool for quantum control and state preparation.
Monitored quantum systems undergo measurement-induced phase transitions (MiPTs) stemming from the interplay between measurements and unitary dynamics. When the detector readout is postselected to match a given value, the dynamics is generated by a non-Hermitian Hamiltonian with MiPTs characterized by different universal features. Here, we derive a stochastic Schrödinger equation based on a microscopic description of continuous weak measurement. This formalism connects the monitored and postselected dynamics to a broader family of stochastic evolution. We apply the formalism to a chain of free fermions subject to partial postselected monitoring of local fermion parities. Within a two-replica approach, we obtain an effective bosonized Hamiltonian in the strong postselected limit. Using a renormalization group analysis, we find that the universality of the non-Hermitian MiPT is stable against a finite (weak) amount of stochasticity. We further show that the passage to the monitored universality occurs abruptly at finite partial postselection, which we confirm from the numerical finite size scaling of the MiPT. Our approach establishes a way to study MiPTs for arbitrary subsets of quantum trajectories and provides a potential route to tackle the experimental postselected problem.
We study continuously monitored dynamics of a quasiperiodic free-fermion chain defined on a Fibonacci lattice. We focus on fluctuations of the local particle number, which exhibit a spatially uniform distribution in the unitary limit. Remarkably, we demonstrate that they exhibit a nonuniform spatial pattern originating from the quasiperiodic long-range order under continuous measurement. Furthermore, employing both physicaland perpendicular-space analyses, we elucidate that measurement-induced crossover emerges in fluctuations due to the interplay between the incommensurate modulation and the continuous measurement. While weak measurement yields a distribution reflecting the long-range spatial structure of the quasiperiodic system, an increase in measurement strength alters the distribution into one dominated by the local environment of each site. We also elucidate that the measurement-induced crossover emerges in other physical quantities such as connected correlation functions. These findings offer insights into nonequilibrium quasiperiodic phenomena emerging in continuously monitored dynamics.
We study the dynamics under continuous measurements for free fermions in a quasiperiodic potential by using the Aubry-Andr\'e-Harper model with hopping rate JJJ and potential strength VVV. On the basis of the quantum trajectory method, we obtain the phase diagram for the steady-state entanglement entropy and demonstrate that robust logarithmic system-size scaling emerges up to a critical potential strength ${V}_{c}/J\ensuremath{\sim}2.3$. Moreover, we find that the measurement induces entanglement phase transitions from the logarithmic-law phase to the area-law phase for the potential strength V<VcV<{V}_{c}V<Vc​, while any finite measurement stabilizes the area-law phase for V>VcV>{V}_{c}V>Vc​. This result is distinct from the entanglement scaling in the unitary limit, where volume-law and area-law phases undergo a transition at V/J=2V/J=2V/J=2. To further support the phase diagram, we analyze the connected correlation function and find that it shows algebraic decay in the logarithmic-law phase, while it decays quickly in the area-law phase. Our results can be tested in ultracold atoms by introducing quasiperiodic potentials and continuously monitoring the local occupation number with an off-resonant probe light.
Abstract We present a numerical study of measurement-induced suppression of coherent tunneling in a two-level quantum system subject to re peated projective monitoring. The dynamics are simulated using a stochastic quantum-trajectory (Monte-Carlo) unraveling which repro duces the dephasing dynamics of a continuously monitored system. We introduce an effective measurement rate γ ≈ pmeas/dt and demon strate a monotonic reduction of the escaped population as a function of γ/∆, where ∆ is the coherent tunneling amplitude. For a fixed evolution time T = π/2, we observe a clear transition to the quantum Zeno regime for γ ≫ ∆. A log–log analysis of the large-γ data re veals an asymptotic scaling close to Pesc ∝ γ−1, in agreement with the strong-measurement limit of the corresponding Lindblad master equation. Our results provide a compact and programmable numerical platform for investigating measurement-controlled tunneling dynamics and Zeno-based control using gate-level quantum simulation frame works.
We show that the entanglement entropy (EE) of one-dimensional (1d) non-interacting fermions with U(1)U(1)U(1) symmetry in the presence of a disordered or quasi-periodic potential in which the occupation number is being monitored by homodyne or projection protocols is always in an area-law phase so no measurement induced phase transition (MIPT) occurs. The reason for the previously claimed MIPT in these systems was a finite size effect related to the fact that the maximum lattice size L≃500L \simeq 500L≃500 was of the order of the correlation length. By increasing the system size up to L≃18000L \simeq 18000L≃18000, employing Graphics Processing Units (GPUs), and performing a careful finite-size scaling analysis, we find that the critical monitoring strength is consistent with zero, so no MIPT occurs. For the disordered case, these numerical results are fully supported by an analytical calculation based on mapping the problem onto a nonlinear sigma model (NLSM) that confirms the absence of the MIPT for any monitoring or disorder strength. The effect of disorder is captured by a change of symmetry from BDI to AIII, which results in an enhanced correlation length in the weak disorder limit, and by an effective monitoring strength that increases linearly with disorder.
We present a theoretical and numerical study of measurement-induced phase transitions and quantum Zeno dynamics in continuously monitored open many-body systems. Moving beyond closed unitary systems, we investigate the competition between chaotic unitary evolution and continuous weak measurements by employing the stochastic Schrödinger equation (quantum jump Monte Carlo) formalism and non-hermitian effective Hamiltonians. Our analysis examines the transition from area-law to volume-law entanglement scaling, mutual information properties, and the critical scaling hypothesis near the measurement-rate threshold. Furthermore, we derive original analytical estimates for the quantum correlation damping decrement in the regime of strong Zeno suppression and validate the theoretical findings using stochastic trajectory numerical simulation protocols with finite-size scaling.