Experimental observation of controllable kinetic constraints in a cold atomic gas

Abstract

Many-body systems relaxing to equilibrium can exhibit complex dynamics even if their steady state is trivial. In situations where relaxation requires highly constrained local particle rearrangements, such as in glassy systems, this dynamics can be difficult to analyze from first principles. The essential physical ingredients, however, can be captured by idealized lattice models with so-called kinetic constraints. While so far constrained dynamics has been considered mostly as an effective and idealized theoretical description of complex relaxation, here we experimentally realize a many-body system exhibiting manifest kinetic constraints and measure its dynamical properties. In the cold Rydberg gas used in our experiments, the nature of the kinetic constraints can be tailored through the detuning of the excitation lasers from resonance. The system undergoes a dynamics which is characterized by pronounced spatial correlations or anticorrelations, depending on the detuning. Our results confirm recent theoretical predictions, and highlight the analogy between the dynamics of interacting Rydberg gases and that of certain soft-matter systems. DOI: 10.1103/PhysRevA.93.040701 Complex collective relaxation in many-body systems is often accompanied by a dramatic slowdown of diffusion processes and the emergence of nonergodic and glassy phases [1][2][3][4]. At low temperatures or high densities their evolution is often dominated by steric hindrances affecting particle motion. Local rearrangements are highly constrained, giving rise to collective-and often slow-relaxation. These features can be seen to be the consequence of effective kinetic constraints in the dynamics [5]. A kinetic constraint is a condition on the rate for a local transition dependent on the local environment: The transition and its reverse-irrespective of whether they are energetically favorable or unfavorable-can only occur if the constraint is satisfied. Kinetic constraints [6] can severely restrict relaxation in situations where local particle arrangements make satisfying them unlikely, which is typical of fluid systems with excluded volume interactions such as dense colloids or supercooled liquids [1][2][3][4]. When a constraint is satisfied, however, the transition is allowed and a local rearrangement is "facilitated" [5,6]. Kinetic constraints naturally give rise [7] to collective and spatially heterogeneous relaxation, and are used to describe situations where the correlation properties of the dynamics go beyond those of the static stationary state, a salient feature of glassy systems [4].Steric hindrances and dynamic facilitation are argued to play a central role in the behavior of glass formers [5]. However, it can be difficult [8] to establish unambiguously the relation between microscopic processes and emerging kinetic constraints, or between idealized models with explicit kinetic constraints and actual physical systems. In this Rapid Communication we establish such a direct connection by reporting the experimental observation of correlated...

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Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations

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