KPZ Growth Law Confirmed in 2D After 40 Years
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- University of Würzburg researchers from the Cluster of Excellence ctd.qmat achieved the first experimental confirmation of the 1986 Kardar–Parisi–Zhang (KPZ) equation in two-dimensional systems, publishing the result in Science (Widmann et al., DOI: 10.1126/science.aeb4154).
- The team injected polaritons—hybrid light-matter particles—into a gallium arsenide semiconductor cooled to −269.15°C, exploiting the particles' picosecond-scale non-equilibrium lifetimes to track spatial and temporal growth dynamics simultaneously.
- A 2022 Paris experiment had previously confirmed KPZ behavior only in one-dimensional systems; the Würzburg result extends the universality class to 2D surfaces and interfaces for the first time.
- Sebastian Diehl of the University of Cologne, a member of the research team, developed the theoretical concept of testing KPZ universality in a polariton quantum system, with the underlying theoretical groundwork dating to 2015.
- Researchers used molecular beam epitaxy to engineer atomically precise mirror layers that confine photons into a central quantum film, enabling the laser to excite the sample with micrometer precision.
- The KPZ framework governs growth processes across physics, mathematics, biology, and computer science—from crystal formation, bacterial colonies, and flame fronts to machine-learning algorithm development—wherever nonlinear, random surface growth occurs.
- Postdoctoral researcher Siddhartha Dam and doctoral researcher Simon Widmann conducted the experiments at the University of Würzburg's Chair of Technical Physics, with Dam noting that controlling a non-equilibrium quantum system in the lab has only recently become technically feasible.
Why it matters: By experimentally confirming KPZ universality in 2D—after 40 years of the equation's existence—this result validates a single theoretical framework for surface growth across crystals, bacterial colonies, and flame fronts, giving researchers a reliable experimental handle on non-equilibrium quantum systems that was previously restricted to 1D models.
