Abstract
Isolated quantum many-body systems with integrable dynamics generically do not thermalize when taken far from equilibrium. As one perturbs such systems away from the integrable point, thermalization sets in, but the nature of the crossover from integrable to thermalizing behavior is an unresolved and actively discussed question. We explore this question by studying the dynamics of the momentum distribution function in a dipolar quantum Newton's cradle consisting of highly magnetic dysprosium atoms. This is accomplished by creating the first one-dimensional Bose gas with strong magnetic dipole-dipole interactions. These interactions provide tunability of both the strength of the integrability-breaking perturbation and the nature of the near-integrable dynamics. We provide the first experimental evidence that thermalization close to a strongly interacting integrable point occurs in two steps: prethermalization followed by near-exponential thermalization. Exact numerical calculations on a two-rung lattice model yield a similar two-timescale process, suggesting that this is generic in strongly interacting near-integrable models. Moreover, the measured thermalization rate is consistent with a parameter-free theoretical estimate, based on identifying the types of collisions that dominate thermalization. By providing tunability between regimes of integrable and nonintegrable dynamics, our work sheds light both on the mechanisms by which isolated quantum many-body systems thermalize, and on the temporal structure of the onset of thermalization.
Highlights
In classical physics, chaos and the approach to thermal equilibrium are intimately related: The irregular spacefilling trajectories of a chaotic system sample all of phase space
Rather than exhibiting thermalization or revivals [1], a nonthermal momentum distribution persisted to long times
We explore the onset of thermalization in a nearly integrable, strongly interacting system—an array of dipolar quantum Newton’s cradles consisting of dysprosium atoms—subject to an integrability-breaking perturbation of tunable strength, namely, the magnetic dipole-dipole interaction (DDI); see Fig. 1(a) [31]
Summary
Chaos and the approach to thermal equilibrium are intimately related: The irregular spacefilling trajectories of a chaotic system sample all of phase space. Rather than exhibiting thermalization or revivals [1], a nonthermal momentum distribution persisted to long times Such long-lived, nonthermal states are often termed prethermal states and are naturally present in nearly integrable systems; they have been experimentally observed in weakly interacting, quasi-1D quantum gases [28,29,30]. There is no theoretical consensus even on the basic question of whether relaxation involves two distinct timescales or three [13,14,17,18,19] Motivated by these findings, we explore the onset of thermalization in a nearly integrable, strongly interacting system—an array of dipolar quantum Newton’s cradles consisting of dysprosium atoms—subject to an integrability-breaking perturbation of tunable strength, namely, the magnetic dipole-dipole interaction (DDI); see Fig. 1(a) [31]. Based on our experimental observations, we argue that the thermalization rate depends on the strength of the integrability-breaking perturbation, but on the parameters of the integrable model itself
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