We have fabricated a double quantum dot device with two lateral gates, and measured to electrical transport properties at low temperature. Previous work on single hole charging in trench isolated single quantum dot structures has been shown to exhibit clear Coulomb blockade effects (1,2). Here we observe a change in the period of the Coulomb oscillations in conductance, which strongly suggests that a tunnel barrier can be lowered completerly by application of a suitable gate voltage. A large reduction in the noise on the oscillation current is also observed when all tunnel barriers are restored. This is explained by a filtering effect due to the discrete levels in each dot.
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