  Ultrafast stimuli can stabilize metastable states of matter inaccessible by
equilibrium means. Establishing the spatiotemporal link between ultrafast
excitation and metastability is crucial to understanding these phenomena. Here,
we use single-shot optical-pump, X-ray-probe measurements to provide snapshots
of the emergence of a persistent polar vortex supercrystal in a heterostructure
that hosts a fine balance between built-in electrostatic and elastic
frustrations by design. By perturbing this balance with photoinduced charges, a
starting heterogenous mixture of polar phases disorders within a few
picoseconds, resulting in a soup state composed of disordered ferroelectric and
suppressed vortex orders. On the pico-to-nanosecond timescales, transient
labyrinthine fluctuations form in this soup along with a recovering vortex
order. On longer timescales, these fluctuations are progressively quenched by
dynamical strain modulations, which drive the collective emergence of a single
supercrystal phase. Our results, corroborated by dynamical phase-field
modeling, reveal how ultrafast excitation of designer systems generates
pathways for persistent metastability.
