  The interfacial coupling of two materials with different ordered phases, such
as a superconductor (S) and a ferromagnet (F) is driving new fundamental
physics and innovative applications. For example, the creation of spin-filter
Josephson junctions and the demonstration of triplet supercurrents have
suggested the potential of a dissipationless version of spintronics based on
unconventional superconductivity. Here we demonstrate evidence for active
quantum applications of S-F-S junctions, through the observation of macroscopic
quantum tunneling in Josephson junctions with GdN ferromagnetic insulator
barriers. We prove a clear transition from thermal to quantum regime at a
crossover temperature of about 100 mK at zero magnetic field in junctions which
demonstrate a clear signature of unconventional superconductivity. Following
previous demonstration of passive S-F-S phase shifters in a phase qubit, our
result paves the way to the active use of spin filter Josephson systems in
quantum hybrid circuits.
