  Graphene and bilayer graphene quantum dots are promising hosts for spin
qubits with long coherence times. Although recent technological improvements
make it possible to confine single electrons electrostatically in bilayer
graphene quantum dots, and their spin and valley texture of the single particle
spectrum has been studied in detail, their relaxation dynamics remains still
unexplored. Here, we report on transport through a high-frequency gate
controlled single-electron bilayer graphene quantum dot. By transient current
spectroscopy of single-electron spin states, we extract a lower bound of the
spin relaxation time of 0.5~$\mu$s. This result represents an important step
towards the investigation of spin coherence times in graphene-based quantum
dots and the implementation of spin-qubits.
