A sparse quantum dot crossbar with sublinear scaling of interconnects at cryogenic temperature*

A practical spin-based quantum computer will require millions of qubits that operate at cryogenic temperature and interface to room temperature with only a few electrical wires. Sublinear scaling of interconnects is also required for a high-throughput fabrication-measurement cycle of quantum devices. We demonstrate a 36x36 gate electrode crossbar that supports 648 narrow-channel field effect transistors (FET) for gate-defined quantum dots and enables a quadratic increase in quantum dot device count with a linear increase in control lines. The multi-gate FET are fabricated on industrial ²⁸Si-MOS stacks and integrate two tunable tunnel barriers per device, with interleaved ohmic contacts and cryo-CMOS control circuitry to measure each device independently from all others. Electrical characterisation at 1.7 K of a grid with geometry variations demonstrates 100% device yield and shows a decreasing threshold voltage for narrow channel devices. Statistical data obtained in this way provide means for device optimisation by design as a stepping stone towards large quantum dot spin-qubit arrays.