OREANDA-NEWS. Nippon Telegraph and Telephone Corp. (NTT) in UK have performed high-accuracy measurements of a single-electron transfer device comprising silicon transistors and demonstrated single-electron transfer at 1 GHz (109 Hz) with a world-record accuracy in the gigahertz regime: an error rate of less than 9.2 ? 10-7.

Since high-accuracy single-electron transfer leads to a current with high accuracy, our result is an important step toward the realization of a current standard, which corresponds to a ruler to measure electric current. A current standard based on the single-electron transfer would be one that could most directly realize the ampere (the base unit of electric current), which, according to a recent proposal, should be redefined. Furthermore, it could be used for the quantum metrology triangle experiments, which check the consistency of fundamental physical constants. This would significantly contribute to the field of the fundamental physics.

This work will be published in the online version of “Applied Physics Letters” on the 5th of July, 2016 (EST).

It was proposed in 2011 that the International System of Units (SI) be redefined using invariants of nature such as the Planck constant h and the elementary charge e . In the redefinition, the definition of the ampere (the base unit of electric current) will be changed. The new ampere will be set by generating a current e? (?: frequency) using a current standard, with the numerical value of e fixed (e is now a measured value). Since a single-electron transfer device, which can convey electrons one by one using clock control, connects e to the ampere), it is attracting much attention as a device that could be used for the most direct current standard. Furthermore, if a high-accuracy current standard based on single-electron transfer is realized, it could be used for the quantum metrology triangle experiments. Since such experiments will enable us to check the consistency of fundamental physical constants, they will contribute to the field of fundamental physics.

A practical current standard must operate at high speed, corresponding to a high current level, with high accuracy. Toward this goal, NTT Basic Research Laboratories have been studying single-electron transfer devices using silicon transistors. Silicon nanofabrication techniques accumulated over time have succeeded in greatly reducing the size of silicon devices. This is important for achieving high-accuracy operation suitable for the current standard. To show the expected high-accuracy operation, we needed a detailed evaluation of the transfer accuracy, but the measurement condition had not been optimized. In addition, gallium arsenide-based single-electron transfer devices, in which high accuracy was previously reported, have not been able to operate at more than 1 GHz without a significant loss of accuracy.

NTT Performed high-accuracy measurements of a current generate using a silicon single-electron transfer device comprising silicon transistors at 1 GHz and achieved a world-record accuracy in the gigahertz regime: a transfer error rate of less than 9.2 ? 10-7 . The silicon single-electron transfer device was fabricated by NTT, and the measurements were performed by using high-accuracy current measurement system at National Physical Laboratory (NPL) in UK. The value is about two orders magnitude better than that obtained from conventional measurements of silicon single-electron transfer devices. In addition, we performed a similar experiment at 2 GHz, which shows an error rate of about 3 ? 10-6. This indicates that our device breaks the 1-GHz barrier and is suitable for high-speed operation.