Coulomb blockade electrometer based on single cooper pair tunneling

We have studied the electrometric characteristics of the Bloch transistor, i.e. the structure comprising a double small-capacitance superconductor junction (where both the Josephson and the charging energies, E(J1,2)similar to E(C1,2)much greater than k(B)T) and an adjacent gate electrode polarizing its island. The transistor bias is realized through small-sized high-ohmic resistors (much greater than R-Q = h/4e(2)approximate to 6.5 k Ohm) to ensure a high electromagnetic impedance of the transistor environment. At low bias current, a coherent flow of single Cooper pairs occurs and the average voltage across the transistor shows a 2e-periodic dependence on the polarization charge Q(0). The sensitivity of such an electrometer has been evaluated and found to be comparable to that of the single-electron counterpart. The device has been fabricated with Al/AlOx/Al junctions and two miniature on-chip Cr resistors (each of 80 k Ohm and 10 mu m long) which were located very close to the junctions. We used this device to measure 1/f noise of the background charge and found it to be about 9 x 10(-4) e/Hz(1/2) at 10 Hz. (C) 1999 Elsevier Science Ltd. All rights reserved.