Inductively read superconducting SET (L-SET)

P. Hakonen, L. Roschier, and M. Sillanpää

Rf-SET electrometry, previously performed successfully on MWNTs, has been extended towards inductive read-out schemes in superconducting Cooper pair transistors (SSET). In our setup, the charge-induced change of SSET inductance was determined using reflection measurements at frequencies around 700 MHz. The back action of this kind of electrometer is basically governed by the preamplifier, the contribution of which we reduced by using a circulator at mixing chamber temperature. The best charge sensitivity, ~ 10-4 e/, was achieved in an operation mode which took advantage of the nonlinearity of the Josephson potential. According to our simulations, quantum limited performance (~ 10-6 e/), should be within reach using samples where the ratio of Josephson and Coulomb energies is reduced down to 0.3.