Observation of Floquet prethermalization in dipolar spin chains*

Periodically driven (Floquet) quantum systems provide a promising platform to study physics out of equilibrium, such as time crystalline phase and Floquet topological structure. However, the drive generically heats up the system to infinite temperature.
Still, it was shown theoretically that the heating rate is exponentially small in the driving frequency, giving rise to a long-lived prethermal stage that exhibits all the intriguing properties of Floquet systems.
Here we present nuclear magnetic resonance observation of Floquet prethermalization in dipolar spin chains. We first show that the system quickly converges to a prethermal state that agrees with the equilibrium statistics of a time-independent “prethermal” Hamiltonian (PTH). We then observe the exponentially slow heating of quasi-conserved quantities, by measuring the time-autocorrelation of the PTH itself. Intriguingly, we find that at timescale when the PTH is no longer conserved, the system may still possess other symmetries.
The results improve our understanding of thermalization in driven quantum systems and demonstrate the possibility to realize novel Floquet phases of matter and robust Floquet engineering in the prethermal regime.