Storage capabilities of a four-junction single-electron trap with an on-chip resistor

We report on the operation of a single-electron trap comprising a chain of four Al/AlOx/Al tunnel junctions attached, at one side, to a memory island and, at the other side, to a miniature on-chip Cr resistor (R≈50 kΩ), which served to reduce cotunneling. At appropriate voltage bias, the bistable states of the trap, with the charges differing by the elementary charge e, were realized. At low temperature, spontaneous switching between these states was found to be very infrequent. For instance, at T=70 mK the system was capable of holding an electron for more than 2 h, this time being limited by the time of the measurement.