  In the emergent field of quantum technology, the ability to manage heat at
the nanoscale and in cryogenic conditions is crucial for enhancing device
performance in terms of noise, coherence, and sensitivity. Here, we demonstrate
the active cooling and refrigeration of the electron gas in a graphene thermal
transistor, by taking advantage of nanoscale superconductive tunnel contacts
able to pump or extract heat directly from the electrons in the device. Our
prototypes achieved a top cooling of electrons in graphene of about 15 mK at a
bath temperature of about 450 mK, demonstrating the viability of the proposed
device architecture. Our experimental findings are backed by a detailed thermal
model that accurately replicated the observed device behavior. Alternative
cooling schemes and perspectives are discussed in light of the reported
results. Finally, our graphene thermal transistor could find application in
superconducting hybrid quantum technologies.
