ADVANTAGES OF SUPERCONDUCTING COULOMB-BLOCKADE ELECTROMETERS

We have measured the current-voltage-gate charge characteristics and n oise in superconducting Coulomb-blockade electrometers from 50 mK to 1 .05 K. The Al-AlOx-Al junctions in our devices have capacitances which range from 0.3 fF to 1 fF and tunneling resistances from 20 k Ohm to 200 k Ohm. We find that our normal and superconducting electrometers h ave comparable Charge noise but that the latter have much larger modul ation which persists to significantly higher temperatures. The maximum operating temperature in the superconducting state is close to T-c. T his behavior is consistent with a simple model and makes the supercond ucting electrometer preferable for many applications.