2023 James Joule Medal and Prize

Professor Jan-Theodoor Janssen has made world-leading contributions to the field of single-electron transport and the quantum Hall effect (QHE) for electrical metrology. The international system of units (the SI) was redefined in May 2019. The system has moved from units based on artefacts and difficult-to-realize definitions to one based on fundamental constants of nature. This is the most important change to the SI in a century and has been preceded by many decades of intense research. Janssen has led ground-breaking research on two important SI units: the ampere and the ohm. In both these cases, his work has been highly original and world leading, resulting in several orders of magnitude improvement in accuracy, thereby enabling the long-held ambition of redefining the SI. The impact of Janssen’s research stretches well beyond the immediate metrology sphere and also benefits applications based on quantum technology and graphene.

The new definition of the ampere is based on the elementary charge, e. In 2007, Janssen developed a new technique to transport electrons with his long-term collaborator Professor Sir Michael Pepper. Over subsequent years, Janssen and his team have made this type of electron pumping more and more accurate through several ingenious improvements. The technique of tuneable barrier pumping has been adopted by many other laboratories around the world and has become the de-facto method for realizing the new definition of the ampere. Highly accurate electron pumps are now used in a variety of quantum technology applications; for example, electron quantum optics.

Janssen’s research on the QHE in graphene has transformed the field of primary resistance metrology with most leading metrology laboratories following his lead. In 2010, Janssen and his group succeeded in achieving an astonishingly accurate QHE (parts in 10¹¹) in graphene. The importance of this result was recognized by its inclusion in the 2012 Committee on Data of the International Science Council evaluation of fundamental constants. He has developed a tabletop QHE system that is being commercialized for other metrology laboratories and high-end electronics manufacturers, giving them direct access to quantum standards.