Long-Range Gates in Superconducting Dual-Rail Qubits (Part2 - Design)

The ability to perform simultaneous two-qubit gates between many pairs of more-than-nearest-neighbor qubits is a significant advantage for quantum processors, affording efficient routing of information, flexibility in gate compilation, and implementation of non-local check operators for quantum error correction codes such as qLDPC codes that have encoding rate advantages over local codes like the surface code. Existing superconducting quantum processors have implemented nearest-neighbor coupling architectures which have been practically limited to local quantum error correction codes. We report on the design of a superconducting device intended to implement simultaneous long-range two-qubit gates between many pairs of dual-rail transmon (DRT) qubits coupled to a multi-mode one-dimenisional coupled-resonator array bus by using a cross-resonance interaction between the qubits and the long-range modes of the bus. We discuss parameter regime tradeoffs and how the architecture can reduce unwanted cross-Kerr couplings between pairs of qubits and between qubits and bus modes and how it mitigates gate crosstalk, making the implementation of simultaneous long-range gates feasible. We comment on scaling challenges and future directions.