  Graphene double quantum open the possibility to use charge or spin degrees of
freedom for storing and manipulating quantum information in this new electronic
material. However, impurities and edge disorders in etched graphene
nano-structures hinder the ability to control the inter-dot tunnel coupling,
tc,the most important property of the artificial molecule. Here we report
measurements of tc in an all-metal-gates-tuned graphene DQD. We find that tc
can be controlled continuously about a factor of four by employing a single
gate. Furthermore, tc, can be changed monotonically about another factor of
four as electrons are gate-pumped into the dot one by one. The results suggest
that the strength of tunnel coupling in etched DQDs can be varied in a rather
broad range and in a controllable manner, which improves the outlook to use
graphene as a base material for qubit applications.
