Control of the electromagnetic environment for single Josephson junctions using arrays of dc SQUIDs

We have measured the current–voltage characteristics of small-capacitance single Josephson junctions at low temperatures T ≤ 0.04 K, where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. When the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e 2 ≈ 26 kΩ, a transition to a clear Coulomb blockade of Cooper-pair tunnelling is induced in the single junction. The measured blockade voltage agrees with the theoretical prediction.