  Microscopic studies on thin film superconductors play an important role for
probing non-equilibrium phase transitions and revealing dynamics at the
nanoscale. However, magnetic sensors with nanometer scale spatial and
picosecond temporal resolution are essential for exploring these. Here, we
present an all-optical, microwave-free method, that utilizes the negatively
charged nitrogen-vacancy (NV) center in diamond as a non-invasive quantum
sensor and enables the spatial detection of the Meissner state in a
superconducting thin film. We place an NV implanted diamond membrane on a
superconducting LSCO thin film. The strong B-field dependence of the NV
photoluminescence (PL) allows us to investigate the Meissner screening in LSCO
under an externally applied magnetic field in a non-resonant manner.
