Long hold times in a two-junction electron trap

The hold time τ of a single-electron trap is shown to increase significantly due to suppression of photon assisted tunneling events. Using two rf-tight radiation shields instead of a single one, we demonstrate increase of τ by a factor exceeding 103, up to about 10 h, for a trap with only two superconductor (S)—normal-metal (N) tunnel junctions and an on-chip resistor R ∼ 100 kΩ (R-SNS structure). In the normal state, the improved shielding made it possible to observe τ ∼ 100 s, which is in reasonable agreement with the quantum-leakage-limited level expected for the two-electron cotunneling process.