  The ultimate spatial limit to establish a Josephson coupling between two
superconducting electrodes is an atomic-scale junction. The Josephson effect in
such ultrasmall junctions has been used to unveil new switching dynamics, study
coupling close to superconducting bound states or unveil non-reciprocal
effects. However, coupling is weak and thermal smearing reduces the Cooper pair
current magnitude. Here we show that a feedback element induces a
time-dependent bistable regime which consists of periodic oscillations between
two different Cooper pair tunneling states (corresponding to the DC and AC
Josephson regimes respectively). The amplitude of the time-averaged current
within the bistable regime is robust against thermal smearing. By tracing the
periodic oscillations in the new bistable regime as a function of the position
in a Scanning Tunneling Microscope (STM), we obtain atomic scale map of the
critical current in 2H-NbSe$_2$ and find spatial modulations due to a pair
density wave. Our results fundamentally improve our understanding of atomic
size Josephson junctions and provide a promising new route to study
superconducting materials through atomic scale maps of the Josephson coupling.
