  We have employed a tunable Cooper-pair transistor, the sluice, with radio
frequency control to pump current over a resistive circuit. We find that the
charge transferred per pumping cycle can be controlled with the resolution of a
single Cooper-pair up to hundreds of pairs. The achieved nanoampere current
features more than an order of magnitude improvement over the previously
reported results and it is close to the theoretical maximum value for the
measured sample.
