Long hold times in a two-junction electron trap
  The hold time $\tau$ of a single-electron trap is shown to increase significantly due to suppression of environmentally assisted tunneling events. Using two rf-tight radiation shields instead of a single one, we demonstrate increase of $\tau$ by a factor exceeding $10^3$, up to about 10 hours, for a trap with only two superconductor (S) -- normal-metal (N) tunnel junctions and an on-chip resistor $R$ (R-SNS structure). In the normal state, the improved shielding made it possible to observe $\tau\sim$ 100 s, which is in reasonable agreement with the quantum-leakage-limited level expected for the two-electron cotunneling process. 
A. Kemppinen, S. V. Lotkhov, O.-P. Saira, A. B. Zorin, J. P. Pekola,   and A. J. Manninen
cond-mat.mes-hall cond-mat.supr-con