  Coherent optical driving in quantum solids is emerging as a new research
frontier, with many demonstrations of exotic non-equilibrium quantum phases.
These are based on engineered band structures, and on stimulated nonlinear
interactions between driven modes. Enhanced functionalities like
ferroelectricity, magnetism and superconductivity have been reported in these
non-equilibrium settings. In high-Tc cuprates, coherent driving of certain
phonon modes induces a transient state with superconducting-like optical
properties, observed far above T$_c$ and throughout the pseudogap phase.
Questions remain not only on the microscopic nature of this phenomenon, but
also on the macroscopic properties of these transient states, beyond the
documented optical conductivities. Crucially, it is not clear if driven
cuprates exhibit Meissner-like diamagnetism. Here, the time-dependent
magnetic-field amplitude surrounding a driven YBa$_2$Cu$_3$O$_{6.48}$ sample is
probed by measuring Faraday rotation in a GaP layer adjacent to the
superconductor. For the same driving conditions that result in
superconducting-like optical properties, an enhancement of magnetic field at
the edge of the sample is detected, indicative of induced diamagnetism. The
dynamical field expulsion measured after pumping is comparable in size to the
one expected in an equilibrium type II superconductor of similar shape and size
with a volume susceptibility $\chi_v$ of order -0.3. Crucially, this value is
incompatible with a photo-induced increase in mobility without
superconductivity. Rather, it underscores the notion of a pseudogap phase in
which incipient superconducting correlations are enhanced or synchronized by
the optical drive.
