Research
We are theorists who like to work next to experiments. Most of our projects start from a device that someone in Delft or elsewhere can build, and end with a prediction that they can test, or with a tool that makes the next calculation easier. Our current work falls into four connected themes.
Majoranas in quantum-dot chains
Instead of looking for Majorana states in long, disordered nanowires, one can assemble a Kitaev chain from a few quantum dots coupled through superconductors, tuning every parameter separately. We design these minimal chains together with the experimental groups that build them, find how they scale to longer chains, and ask how to make them robust to disorder and interactions and use them as qubits.
Examples: three-site Kitaev chain, Majorana parity qubit, Pareto-optimal Majoranas.
Superconducting hybrids and Andreev qubits
Josephson junctions made from semiconductors and superconductors host Andreev states whose energy, spin, and parity can be controlled with gates. We study how to turn these states into qubits and couplers, how multiterminal circuits behave, and what transport and spectroscopy reveal about the underlying superconductor.
Examples: Kramers-protected error correction with Andreev spin qubits, strain engineering of Andreev spin qubits in germanium, loopless multiterminal circuits.
Topology beyond periodic crystals
Band theory needs a perfect lattice, but real materials and devices are disordered, finite, quasiperiodic, or strongly interacting. We develop ways to identify topological phases directly from scattering, from statistical symmetries of disordered systems, and from many-body models of engineered lattices.
Examples: scattering theory of higher-order topology, statistical topological matter, weak universality with quantum dots.
Computational methods
Numerical simulations are a central instrument in our work, and whenever a method is useful beyond one project, we turn it into a package. We develop algorithms for quantum transport, perturbation theory, and scattering networks, and maintain Kwant, Pymablock, and other packages.
Examples: computational quantum transport review, Pymablock, ScatterWorks.
Earlier work
The group grew out of work on Majorana bound states in nanowires, topological insulators and superconductors, and quantum transport in graphene. Much of that background is covered in our online course Topology in condensed matter. For a complete overview, see our publications. Some of our results were also good-looking enough for a small gallery.