  Magic-angle twisted bilayer graphene (MATBG) hosts a number of correlated
states of matter that can be tuned by electrostatic doping. Superconductivity
has drawn considerable attention and the mechanism behind it is a topic of
active discussion. MATBG has been experimentally characterized by numerous
transport and scanning-probe experiments. The material has also emerged as a
versatile platform for superconducting electronics, as proven by the
realization of monolithic Josephson junctions. However, even though
phase-coherent phenomena have been measured, no control of the superconducting
phase has been demonstrated so far. Here, we present a Superconducting Quantum
Interference Device (SQUID) in MATBG, where the superconducting phase
difference is controlled through the magnetic field. We observe
magneto-oscillations of the critical current, demonstrating long-range
coherence agreeing with an effective charge of 2e for the superconducting
charge carriers. We tune to both asymmetric and symmetric SQUID configurations
by electrostatically controlling the critical currents through the junctions.
With this tunability, we study the inductances in the device, finding values of
up to 2{\mu}H. Furthermore, we directly observe the current-phase relation of
one of the Josephson junctions of the device. Our results show that
superconducting devices in MATBG can be scaled up and used to reveal properties
of the material. We expect this to foster a more systematic realization of
devices of this type, increasing the accuracy with which microscopic
characteristics of the material are extracted. We also envision more complex
devices to emerge, such as phase-slip junctions or high kinetic inductance
detectors.
