  We have 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 tunable
weak link in the middle. 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 $\sqrt{E_J/E_C}$ with a
distinct change in the exponent at $R_0=R_Q=h/4e^2$. 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 QPS
and we show that these are enhanced at the central weak link. Above the
critical voltage a negative differential resistance is observed which nearly
restores the zero-current state.
