Compilation and scaling strategies for a silicon quantum processor with sparse two-dimensional connectivity

Abstract: Inspired by the challenge of scaling up existing silicon quantum hardware, we investigate compilation strategies for sparsely-connected 2d qubit arrangements and propose a spin-qubit architecture with minimal compilation overhead. Our architecture is based on silicon nanowire split-gate transistors which can form finite 1d chains of spin-qubits and allow the execution of two-qubit operations such as Swap gates among neighbors. Adding to this, we describe a novel silicon junction which can couple up to four nanowires into 2d arrangements via spin shuttling and Swap operations. Given these hardware elements, we propose a modular sparse 2d spin-qubit architecture with unit cells consisting of diagonally-oriented squares with nanowires along the edges and junctions on the corners. We show that this architecture allows for compilation strategies which outperform the best-in-class compilation strategy for 1d chains, not only asymptotically, but also down to the minimal structure of a single square. The proposed architecture exhibits favorable scaling properties which allow for balancing the trade-off between compilation overhead and co-location of classical control electronics within each square by adjusting the length of the nanowires. An appealing feature of the proposed architecture is its manufacturability using complementary-metal-oxide-semiconductor (CMOS) fabrication processes. Finally, we note that our compilation strategies, while being inspired by spin-qubits, are equally valid for any other quantum processor with sparse 2d connectivity.