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Measurement-induced phase transitions in informational active matter
Bryan VanSaders1, Michel Fruchart2, Vincenzo Vitelli1,3,4
1James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
PNAS Nexus
|April 13, 2026
Summary
This study introduces adaptive particles that use local measurements to process environmental noise, creating collective behaviors like flocking without external work. This "informational activity" drives active states and offers new applications in self-organizing systems.
Area of Science:
- Statistical Mechanics
- Active Matter Physics
- Information Theory
Background:
- Non-equilibrium systems often function as many-ratchet systems, processing environmental noise via local measurements and information processing, akin to Maxwell's demon.
- These systems challenge traditional coarse-graining methods due to their reliance on decision-making protocols rather than simple force laws.
Purpose of the Study:
- To investigate a many-body generalization of the Maxwell demon problem using a fluid of adaptive particles.
- To elucidate how microscopic decision-making protocols, rather than forces, generate macroscopic active states sustained by measurements.
Main Methods:
- Utilized a combination of information-theoretic, kinetic, and hydrodynamic tools.
- Analyzed collective behavior in adaptive particles that bias noise-driven scattering events based on local measurements.
Main Results:
- Demonstrated the emergence of macroscopic active states driven by microscopic decision-making protocols and continuous measurements.
- Observed an informational flocking phenomenon where the order parameter is information-bounded, potentially indicating a measurement-induced phase transition.
- Identified "informational activity" that compresses phase space without work, leading to deviations from equilibrium scaling with noise magnitude.
Conclusions:
- Microscopic decision-making protocols are key drivers of active states in non-equilibrium systems.
- Measurement-induced phase transitions and informational activity offer novel mechanisms for self-organization and pattern formation.
- Potential applications include noise-induced patterning in microrobot swarms and programmable colloids in turbulent environments.
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