Gate-tunable dissipation and "superconductor-insulator" transition in carbon nanotube josephson junctions

Dissipation is ubiquitous in quantum systems, and its interplay with fluctuations is critical to maintaining quantum coherence. We experimentally investigate the dissipation dynamics in single-walled carbon nanotubes coupled to superconductors. The voltage-current characteristics display gate-tunable hysteresis, with sizes that perfectly correlate with the normal state resistance R_{N}, indicating the junction undergoes a periodic modulation between the underdamped and overdamped regimes. Surprisingly, when a device's Fermi level is tuned through a local conductance minimum, we observe a gate-controlled transition from superconductinglike to insulatinglike states, with a "critical" R_{N} value approximately 8-20 kOmega.