UNDERSTANDING THE BEHAVIOR OF SUPERCONDUCTING COULOMB-BLOCKADE ELECTROMETERS

We report measurements and quantum mechanical simulations of the behav ior of superconducting two-junction Coulomb-blockade electrometers bia sed near the superconducting gap, Our quantum model allows coherent su perpositions of states with different number of charges on the island, It predicts maximum current modulation delta I for devices with tunne ling resistance R-Sigma = 64 pi Delta (h) over bar(2)C(Sigma)(2)/(e(6) tau), where tau is the time for which the system maintains quantum co herence, C-Sigma is the total island capacitance and Delta is the supe rconducting energy gap, For comparison, we built Al-AlOx-Al electromet ers with R-Sigma from 61 k Omega to 1.7 M Omega and C-Sigma ranging fr om 0.9 fF to 8 fF, We find good agreement for tau approximate to 0.35 nsec.