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From financial markets and neuronal activity in the brain to the way forest fires and diseases spread, the dynamics of complex systems are governed by critical events and emergent phenomena that are exceedingly difficult to understand or predict from underlying principles. We recently discovered that a gas of ultracold atoms continuously driven to strongly-interacting Rydberg states by an off-resonant laser field displays all the hallmarks of complex systems dynamics in a highly-controllable experimental system: (i) At early times we observe rapid growth of Rydberg excitations that has a striking correspondence with the spreading of diseases empirically observed in epidemics [1]; (ii) At later times we find that the system evolves toward a self-organised critical (SOC) state [2], a phenomenon that has been conjectured to explain the abundance of scale-invariant systems found in nature. I will discuss how these experiments can be understood in terms of an emergent atomic network that bridges the gap between mathematical models and empirical observations. This provides the opportunity to identify general principles governing non-equilibrium dynamics and to learn how seemingly universal properties emerge from microscopic physical details.
References:
[1] T. M. Wintermantel et al., Epidemic growth and Griffiths effects on an emergent network of excited atoms. Nature Communications 12, 103 (2021)
[2] S. Helmrich et al., Signatures of self-organized criticality in an ultracold atomic gas. Nature 577, 481-486 (2020)
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