How Peking University Engineers Control Prethermalization via Band Structure

Researchers at Peking University and collaboration institues are University of Cambridge and Technical University of Munich, have uncovered a family of many-body periodic orbits within a periodically driven spin system, challenging expectations about how these systems behave outside of traditionally studied high-frequency conditions. The team, led by Jianan Wang and Yang Hou, reports demonstrating that perturbations to these stable orbits exhibit a description akin to a quasiparticle band structure, a concept more commonly associated with static materials. This work aims to resolve the tension between predictions of stable orbits and established thermodynamic principles. In particular, the researchers show that perturbations away from the stable periodic orbits feature a description akin to a quasiparticle band structure. A long-lived prethermal regime appears when modes around the gapless point are slowly populated. While linear stability analysis predicts that perturbed many-body trajectories remain close to stable periodic orbits, thermodynamic principles dictate that Floquet heating will ultimately set in.

Floquet Systems and Many-Body Periodic Orbits

The stability of complex systems hinges on the discovery of repeating patterns within seemingly chaotic dynamics. This work, detailed in recent findings, moves beyond simply observing prethermalization, a temporary slowing of heating in driven systems, to dissecting the underlying mechanisms that allow for such stability. Researchers at Peking University, along with collaborators, aimed to resolve a fundamental tension in the field. Linear stability analysis suggests that perturbed many-body trajectories remain close to stable periodic orbits, but thermodynamic principles dictate that Floquet heating will ultimately set in. “Our work aims to resolve the tension between these two expectations,” the researchers state, seeking to understand the crossover point between order and chaos. Their approach revealed that perturbations around these orbits exhibit behavior remarkably similar to quasiparticle band structures, a concept typically associated with simpler, static systems. A long-lived prethermal regime appears when modes around the gapless point are slowly populated.

Crucially, the dispersion, or how energy varies with momentum, of these quasiparticles dictates how long this prethermal state lasts. The researchers discovered a parametric dependence of the prethermal lifetime, expressed as R^-W, where R represents the width of the quasiparticle distribution and W is the exponent of the dispersion around the gapless point. This means that both the spread of the quasiparticles and the shape of their energy-momentum relationship can be manipulated to extend the system’s stability.

The pursuit of stable, non-equilibrium states in driven many-body systems has long been hampered by the expectation of Floquet heating, a tendency for energy absorption to lead to thermalization. However, recent investigations into periodically driven spin systems are revealing unexpected pathways to circumvent this fate, moving beyond the established understanding of high-frequency drives and prethermalization. Researchers at Peking University, including Yang Hou, Jianan Wang, Hongzheng Zhao, and others, have uncovered a family of many-body periodic orbits and demonstrated that perturbations away from these orbits can be described using a quasiparticle band structure. The analysis demonstrates that a long-lived prethermal regime appears when modes around the gapless point are slowly populated. The dispersion determines the prethermal lifetime, and tailored further-range interactions can systematically flatten the band minima and further suppress heating. This suggests a powerful route toward stabilizing non-equilibrium phases of matter in driven many-body systems.

Researchers at Peking University are charting the lifespan of prethermalization in driven quantum systems, moving beyond simplistic high-frequency approximations to explore more nuanced behaviors. Their work focuses on the delicate balance between stability and eventual heating, a central question in understanding non-equilibrium physics. The team, comprised of Jianan Wang, Yang Hou, Andrea Pizzi, Johannes Knolle, Roderich Moessner, and Hongzheng Zhao, are contributing equally to this work. Their analysis reveals a surprising connection between the stability of these orbits and the emergence of quasiparticle behavior. Linear stability analysis predicts that perturbed many-body trajectories remain close to stable periodic orbits, but thermodynamic principles dictate that Floquet heating will ultimately emerge at long times. This work aims to resolve the tension between these two expectations, showing that perturbations away from the stable periodic orbits feature a description akin to a quasiparticle band structure. A long-lived prethermal regime appears when modes around the gapless point are slowly populated.

Stabilizing Non-Equilibrium Phases with Band Engineering

Maintaining order within systems constantly bombarded with energy has long been a central challenge in physics, with implications ranging from materials science to fundamental understanding of complex dynamics. Recent work by researchers at Peking University and colleagues offers a novel approach to stabilizing these non-equilibrium phases, not by suppressing energy absorption entirely, but by carefully engineering the way energy disperses within the system. These authors contributed equally to this work. The team uncovered a family of many-body periodic orbits in a periodically driven (Floquet) spin system, operating outside the traditionally assumed high-frequency limit. This is significant because high-frequency drives are typically invoked to avoid complex dynamics, whereas this research actively explores stability at lower frequencies. Crucially, the analysis revealed that perturbations around these stable orbits do not behave chaotically but instead exhibit characteristics remarkably similar to quasiparticles moving within a band structure.

A long-lived prethermal regime appears when modes around the gapless point are slowly populated. This dependence offers a pathway to actively control the system’s stability; by manipulating the band structure, specifically by tailoring further-range interactions to flatten the band minima, researchers can systematically suppress heating. The results demonstrate that the lifetime of these prethermal states can be significantly extended through band-structure engineering, providing a practical route to maintaining stable non-equilibrium phases without relying on extreme driving frequencies. Beyond advancing the theoretical understanding of Floquet many-body dynamics, the framework opens new possibilities for controlling driven quantum systems and could inform the design of future quantum simulators and other quantum technologies that depend on robust, long-lived coherent states.