Scalable Quantum Circuit and Control for a Superconducting Surface Code

TLDR

We present a scalable scheme for executing the error‑correction cycle of a monolithic surface‑code fabric of fast‑flux‑tuneable transmon qubits with nearest‑neighbor coupling. An eight‑qubit unit cell repeats the hardware and coherent control, employing three fixed single‑qubit gate frequencies and a unique detuning pattern per qubit; by pipelining interaction and readout steps of ancilla‑based X‑ and Z‑type stabilizer measurements, the scheme avoids all unwanted second‑order transmon‑transmon interactions except those used in controlled‑phase gates, making it applicable to defect‑based and planar logical qubits, including lattice surgery.

Abstract

We present a scalable scheme for executing the error-correction cycle of a monolithic surface-code fabric composed of fast-flux-tuneable transmon qubits with nearest-neighbor coupling. An eight-qubit unit cell forms the basis for repeating both the quantum hardware and coherent control, enabling spatial multiplexing. This control uses three fixed frequencies for all single-qubit gates and a unique frequency detuning pattern for each qubit in the cell. By pipelining the interaction and readout steps of ancilla-based $X$- and $Z$-type stabilizer measurements, we can engineer detuning patterns that avoid all second-order transmon-transmon interactions except those exploited in controlled-phase gates, regardless of fabric size. Our scheme is applicable to defect-based and planar logical qubits, including lattice surgery.