QuSoft is pleased to announce that John van de Wetering, assistant professor at the University of Amsterdam, has received a KNAW Early Career Award from the Royal Netherlands Academy of Arts and Sciences.
The award goes to early career researchers who have made valuable and innovative contributions to science. Van de Wetering receives it for his work on the ZX-calculus, a visual language for describing quantum computations. He helped turn it into a practical tool for making quantum programs smaller, checking that they are correct, and simulating them on ordinary computers. Van de Wetering is one of this year’s laureates, announced today by the KNAW. The awards will be presented at a ceremony on 1 December.
Quantum computers run programs written as circuits: sequences of operations on qubits. The same computation can be written as many different circuits, and some are much shorter than others. On today’s error-prone hardware every operation you remove counts. The ZX-calculus replaces circuits with diagrams of connected nodes. A small set of rules lets you redraw a diagram without changing the computation it describes. Van de Wetering showed how to use these rules to make quantum programs smaller, to check that a simplified program still does the same thing, and to simulate quantum computations on ordinary computers.
From foundations to software
Van de Wetering did his PhD at Radboud University Nijmegen (2016–2020) under the supervision of Aleks Kissinger. His research had two strands. One asked whether the structure of quantum theory follows from basic principles about information, and it produced new results in the mathematics of Jordan operator algebras and effectus theory. The other, with Kissinger, developed the ZX-calculus into a general-purpose tool. Dr. Van de Wetering developed ways to use this language for optimising quantum computations, verifying the correctness of optimisations, and classically simulating quantum computations. Together they built PyZX, an open-source quantum compiler that can rewrite large quantum computations using ZX diagrams. PyZX is now the backbone of several software tools in academia and industry.
With an NWO Rubicon grant and a Marie Skłodowska-Curie fellowship, Van de Wetering then moved to the University of Oxford. There he and Kissinger began writing the textbook Picturing Quantum Software: An Introduction to the ZX-calculus and Quantum Compilation. A free version has been available online since 2024 (github.com/zxcalc/book), and Cambridge University Press will publish it in 2027.
Simulation, AI and a new Master’s programme
Since joining the University of Amsterdam in 2022, Van de Wetering has worked on using ZX diagrams to simulate quantum computations on classical computers. That work is important for testing quantum hardware and for finding where quantum computers really start to outperform classical ones. In Kissinger & Van de Wetering, Quantum Science and Technology, 2022, they showed that ZX-based rewriting can greatly reduce the cost of such simulations. That cost still grows exponentially for the hardest circuits, but ZX methods push back the point where simulation becomes impossible. In 2024 he received an NWO Veni grant to continue this line of research. (Read more in QuSoft’s news item on this work and in the reference articles at the bottom.)
Alongside his research, Van de Wetering coordinated the setup of the University of Amsterdam’s new Master’s programme in Quantum Computer Science. The programme started in September 2024 with him as programme director, and its first students have now graduated.
About the KNAW Early Career Award
The KNAW Early Career Award encourages the further development of a diverse range of early career scientists and scholars who have made valuable and innovative contributions to science or scientific practice. These contributions may relate to the themes identified in the Recognition & Rewards programme: research, education, impact, patient care (in university medical centres), or leadership. Read the KNAW announcement of this year’s laureates and more about the award.
The award looks beyond research alone, and Van de Wetering’s work reaches in several directions: new theory, open-source software used in academia and industry, a textbook, and a Master’s programme that has just seen its first graduates.
References and further reading
QuSoft article on John’s Veni grant
https://www.nature.com/articles/s42256-025-01001-1
