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  • Open Access

Active Quantum Matter from Monitored Pure-State Dynamics

Jacob F. Steiner1, Felix von Oppen2, and Reinhold Egger3

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Phys. Rev. Lett. 137, 120403 – Published 16 September, 2026

DOI: https://doi.org/10.1103/zhdk-kgzx

Abstract

Quantum many-body systems coupled to out-of-equilibrium reservoirs can behave as active matter and exhibit signs of flocking. However, the resulting steady states are highly mixed and carry only weak quantum signatures. We show that signatures of active matter also arise in ensembles of pure states undergoing monitored quantum dynamics. We consider a spinful Luttinger liquid subject to measurement processes that shuffle spin-up particles to the left and spin-down particles to the right. For weak monitoring strengths and ferromagnetic spin interactions, we find power-law quantum correlations between spin density and charge current, which we identify as a hallmark of active quantum matter. The monitoring plays a dual role, generating the quantum active correlations for weak strengths while driving a Berezinskii-Kosterlitz-Thouless phase transition to a short-range correlated state at larger strengths.

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Phys. Rev. Lett. 137, 120403– Published 16 September, 2026
  • Received 12 March 2026
  • Revised 7 July 2026
  • Accepted 3 September 2026
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