Localizing quantum phase slips in one-dimensional Josephson junction chains

We studied quantum phase-slip (QPS) phenomena in long one-dimensional Josephson junction series arrays with tunable Josephson coupling. These chains were fabricated with as many as 2888 junctions, where one sample had a separately tunable link in the middle of the chain. Measurements were made of the zero-bias resistance, R 0 , as well as current–voltage characteristics (IVC). The finite R 0 is explained by QPS and shows an exponential dependence on with a distinct change in the exponent at R 0 = R Q = h /4 e 2 . When R 0 > R Q , the IVC clearly shows a remnant of the Coulomb blockade, which evolves to a zero-current state with a sharp critical voltage as E J is tuned to a smaller value. The zero-current state below the critical voltage is due to coherent QPSs and we show that these are enhanced when the central link is weaker than all other links. Above the critical voltage, a negative, differential resistance is observed, which nearly restores the zero-current state.