Majorana-Spin Coupling in Planar Germanium

Objective

MaSC (Majorana-Spin Coupling in Planar Germanium) aims to combine Majorana bound states (MBSs) and spin qubits (SQs) in a single, scalable platform: planar Ge/SiGe quantum wells. Such a semiconductor stack is ideal to form gate-defined quantum dots (QDs) hosting state-of-the-art SQs. QD arrays can also host fine-tuned MBSs when coupled by superconductors, implementing a Kitaev chain (KC). This was recently demonstrated in InSb nanowires and planar InSbAs; however, those platforms are not readily compatible with state-of-the-art SQs due to nuclear spins. Therefore, MaSC aims to port KCs to planar germanium and couple MBSs and SQs. To build up to this, MaSC sets three objectives: (1) realise a first, minimal KC in planar germanium; (2) integrate high-impedance on-chip resonators to enable fast, single-shot dispersive readout of the chain; (3) resolve coherent coupling between MBSs and an additional QD hosting one SQ. The approach combines design, nanofabrication, and cryogenic measurements, using established platinum annealing to pattern superconducting PtSiGe to proximitise the QDs and realise a KC, and NbN or NbTiN superconducting strips to integrate field-resilient on-chip resonators, all on the same platform. These deliverables advance the Work Programme by strengthening European capability in quantum nanoelectronics and by establishing a concrete basis for a hybrid quantum computation platform that combines fast SQs with robust MBS memories.