GrapheneMetrology - Improved precision and stability (GraM)

Important results from the project

The aim of the project was to reduce the measurement uncertainty in the realisation of the resistance unit, primarily by reducing the noise associated with the measurements. The improvements made during the course of the project have minimized the type-A uncertainty and improved the uncertainty resulting from the quantisation on the resistance plateau used for the realisations. The project has enabled participation in future international comparison measurements which in turn is a key point for further reduction of the type-B uncertainty.

Expected long term effects

The project has led to a reduction of the measurement uncertainty of the resistance realisation that meets the requirements for the Kibble balance. Some improvements of the type-B uncertainty remain, but the requirements for the Kibble balance have been eased since the start of the project and we currently fulfil the expected uncertainty levels for the Kibble balance measurements. The improved type-A uncertainty has made possible a study on quantum Hall arrays based on graphene, which in the future may replace the Kibble balance resistor with a direct realisation of 100 ohms.

Approach and implementation

The seemingly complex noise pattern was handled by dividing the measurement system into several uncertainty contributions which were each examined in a systematic way. For every detected and solved uncertainty contribution, the nature of the noise changed, and new conclusions could be drawn from the remaining noise pattern. The new dry cryostat from 2018 has been a necessary condition for the success of the project. It has been the enabler of long series of measurements under relatively stable conditions, which in turn allowed for the deeper analysis of the noise in question.