Abstract
Far-from-equilibrium dynamics that lead to self-organization are highly relevant to complex dynamical systems not only in physics but also in life, earth, and social sciences. However, it is challenging to find systems with sufficiently controllable parameters that allow quantitatively modeling of emergent properties. Here, we study a nonequilibrium phase transition and observe signatures of self-organized criticality in a dilute thermal vapor of atoms optically excited to strongly interacting Rydberg states. Electromagnetically induced transparency provides excellent control over the population dynamics and enables high-resolution probing of the driven-dissipative dynamics, which also exhibits phase bistability. Increased sensitivity compared to previous work allows us to reconstruct the complete phase diagram, including in the vicinity of the critical point. We observe that interaction-induced energy shifts and enhanced decay only occur in one of the phases above a critical Rydberg population. This case limits the application of generic mean-field models; however, a modified, threshold-dependent approach is in qualitative agreement with experimental data. Near threshold, we observe self-organized dynamics in the form of population jumps that return the density to a critical value.
4 More- Received 9 February 2019
- Revised 29 January 2020
- Accepted 17 March 2020
DOI:https://doi.org/10.1103/PhysRevX.10.021023
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
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Rydberg Atoms on Fire
Published 29 April 2020
A new experiment reveals unexpected connections between a nonequilibrium phase transition in Rydberg gases and the way fires spread through a burning forest.
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Popular Summary
Self-organization arises in a vast range of complex nonequilibrium systems in physics, biology, economics, and other fields. A particularly intriguing example is self-organized criticality (SOC), where the system is attracted toward a critical point—a sort of tipping point at which the overarching behavior of the system changes dramatically. SOC is at the heart of many examples of complexity in nature such as the spread of forest fires and viruses. However, it is difficult to test such models in experimental settings with a high degree of control over the system parameters. Here, we present a new experimental platform for exploring SOC: a dilute room-temperature vapor of rubidium atoms optically excited to Rydberg states.
The strong interactions between Rydberg atoms (where one or more electrons are highly excited) allow a laser-excited atomic gas to exist in either a high or low excitation phase. By changing the laser’s parameters, we can map out the phase diagram in the vicinity of the system’s critical point. Near the phase transition, we observe self-organized dynamics in the form of excitation avalanches that lead to jumps in the Rydberg density as it returns to a critical value. The measured dynamics resemble other well-known examples of SOC such as forest fires, where trees near to burning trees are more likely to catch fire as well, thus facilitating the spread of fire throughout a forest.
The observed dynamics suggest that Rydberg atoms could provide a model system for further studies of criticality in biology, economics, and condensed-matter physics.