  We have measured a graphene double quantum dot device with multiple
electrostatic gates that are used to enhance control to investigate it. At low
temperatures the transport measurements reveal honeycomb charge stability
diagrams which can be tuned from weak to strong interdot tunnel coupling
regimes. We precisely extract a large interdot tunnel coupling strength for
this system allowing for the observation of tunnel-coupled molecular states
extending over the whole double dot. This clean, highly controllable system
serves as an essential building block for quantum devices in a
nuclear-spin-free world.
