Prethermal rotating-frame solid echo in a dipolar nuclear-spin network.

Floquet prethermalization can endow interacting quantum solids with long-lived, approximately conserved quantities, enabling Hamiltonian engineering and new dynamical probes. Using a hyperpolarized network of dipolar-coupled 13C nuclear spins in diamond driven by pulsed spin-locking, we access a rotating-frame prethermal plateau with quasi-conserved transverse magnetization and cycle-resolved inductive readout. Within this prethermal manifold we observe a robust rotating-frame solid echo: after an apparent decay of the rotating-frame free-induction signal over a delay τ, the magnetization revives at time 2τ following a single (α)y pulse, with maximum amplitude near α≃π/2. The echo envelope decays as a stretched exponential with characteristic time T2'≈13ms. Analytical arguments and toy-model simulations attribute the revival to Floquet micromotion that transfers coherences between operator subspaces, so that only a subset of the many-body dephasing dynamics is inverted by the y pulse. These results translate classic echo physics into the prethermal rotating frame and point to continuously interrogated prethermal spin ensembles as a versatile platform for high-throughput spectroscopy, Hamiltonian engineering, and long-duration quantum sensing.