  A supercurrent transistor is a superconductor-semiconductor hybrid device in
which the Josephson supercurrent is switched on and off using a gate voltage.
While such devices have been studied using DC transport, radio-frequency
measurements allow for more sensitive and faster experiments. Here a
supercurrent transistor made from a carbon nanotube is measured simultaneously
via DC conductance and radio-frequency reflectometry. The radio-frequency
measurement resolves all the main features of the conductance data across a
wide range of bias and gate voltage, and many of these features are seen more
clearly. These results are promising for measuring other kinds of hybrid
superconducting devices, in particular for detecting the reactive component of
the impedance, which a DC measurement can never detect.
