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Single-charge Circuits

Working Group 2.42

Research:

Single-charge Detectors

Development and fabrication of single-charge electrometers for the detection of pumping errors in single electron pumps

Single electron pumps are an essential part of a future quantum standard of the electrical current, which will attribute the electrical current to the electron charge and frequency. Practical applications require quantum currents larger than 100 pA corresponding to a pump frequency of the order of 1 GHz. Previous experiments with single electron pumps resulted in a strong decrease of the attainable accuracy with increasing pump frequency.
One possibility to increase the accuracy is to use several electron pumps connected in series and monitoring the charge of the island capacitors between the pumps. This charge is constant if the pumps are working correct, but it will change by an electron charge if one of the neighboring pumps produces a pumping error. Because such pumping errors are quite rare, they can be detected at high pumping frequencies.
The charge on of the capacitors between the pumps can be monitored with the necessary resolution by means of single electron transistors. In this way pumping errors can be recognized and counted, and the actual quantum current can be corrected.

The Al based single electron transistors are fabricated using the shadow evaporation technique together with the electron pumps on a single chip.

This research was supported within the scope of the EMRP-Project „Quantum Ampere“ from May 2012 to April 2015.