Brennan Undseth

After completing his Bsc in Engineering Physics at the University of Alberta (Canada), he moved to QuTech/TU Delft in The Netherlands to pursue a Msc and PhD in the group of Lieven Vandersypen working on silicon spin qubits for quantum information processing. Notable projects include the characterization and mitigation of crosstalk in multi-spin systems, the control of single-spins at low magnetic fields with baseband-frequency signals, and the implementation of parity checks in a spin-shuttling architecture. Brennan has recently joined Quantum Motion as a Senior Quantum Engineer based in San Sebastián, Spain.

Title: TBC

Recent advances in coherent spin shuttling have made sparse semiconductor spin qubit arrays an appealing solid-state platform to realize quantum processors. The dynamic and long-range connectivity enabled by shuttling is also essential for many quantum error-correction schemes. In a recent work (arXiv:2601.23267, accepted for publication in Nature), we demonstrate a silicon spin-qubit device that comprises a shuttling bus for coherently transporting qubits that can interact at four isolated locations we call bus stops. We dynamically populate the array and tune all single- and two-qubit operations using shuttling and quantum non-demolition spin measurements, without access to charge sensing in most of the device. We achieve universal control of the effective five-qubit processor and select the connectivity required to form a surface-code stabilizer plaquette that supports X- and Z-type parity checks up to weight-four. We use the parity checks to generate multi-qubit entanglement between all qubit combinations in the array and report the genuine entanglement of a five-qubit Greenberger-Horne-Zeilinger state, constituting the largest such state ever constructed with gate-defined semiconductor spins. I will discuss what these results mean for encoding logical qubits in silicon and how the techniques developed in this work can be deployed for more ambitious sparse spin qubit architectures in the future.