  In the strongly interacting limit of the Hubbard model localized
double-occupancies form effective hard-core bosonic excitations, called a
doublons, which are long-lived due to energy conservation. Using time-dependent
density-matrix renormalisation group we investigate numerically the dynamics of
doublons arising from the sudden expansion of a spatially confined
band-insulating state in one spatial dimension. By analysing the occupation
scaling of the natural orbitals within the many-body state, we show that
doublons dynamically quasicondense at the band edges, consistent with the
spontaneous emergence of an eta-quasicondensate. Building on this, we study the
effect of periodically driving the system during the expansion. Floquet
analysis reveals that doublon-hopping and doublon-repulsion are strongly
renormalised by the drive, breaking the eta-SU(2) symmetry of the Hubbard
model. Numerical simulation of the driven expansion dynamics demonstrate that
the momentum in which doublons quasicondense can be controlled by the driving
amplitude. These results point to new pathways for engineering non-equilibrium
condensates in fermionic cold-atom experiments and are potentially relevant to
driven solid-state systems.
