Abstract
The theory of continuous phase transitions predicts the universal collective properties of a physical system near a critical point, which for instance manifest in characteristic power-law behaviours of physical observables. The well-established concept at or near equilibrium, universality, can also characterize the physics of systems out of equilibrium. The most fundamental instance of a genuine non-equilibrium phase transition is the directed percolation (DP) universality class, where a system switches from an absorbing inactive to a fluctuating active phase. Despite being known for several decades it has been challenging to find experimental systems that manifest this transition. Here we show theoretically that signatures of the DP universality class can be observed in an atomic system with long-range interactions. Moreover, we demonstrate that even mesoscopic ensembles—which are currently studied experimentally—are sufficient to observe traces of this non-equilibrium phase transition in one, two and three dimensions.
Highlights
Long range correlations can lead to the emergence of collective behaviours which can be distinctively different from the single-body physics governing the constituents
At a so-called critical point, the correlation length of the system diverges and the overall behaviour is fundamentally determined by certain properties — such as dimensionality, range of interactions and symmetries — that do not depend on the specific scale
Phase transitions can take place in the properties of the steady state; this typically leads to an enrichment of the stationary phase diagram which depends upon the coarse-grained aspects of the dynamics, such as symmetries and conservation laws
Summary
Long range correlations can lead to the emergence of collective behaviours which can be distinctively different from the single-body physics governing the constituents. At a so-called critical point, the correlation length of the system diverges and the overall behaviour is fundamentally determined by certain properties — such as dimensionality, range of interactions and symmetries — that do not depend on the specific scale. All systems sharing these few coarse-grained features display the same qualitative macroscopic physics [4] and form a universality class, which is in turn characterized by the corresponding critical exponents and ratios [1, 2, 3, 5].
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