Scalable quantum circuit and control for a superconducting surface code

TL;DR

This paper proposes a scalable quantum control scheme for superconducting surface codes using fixed-frequency transmon qubits, enabling efficient error correction with spatial multiplexing and pipelined stabilizer measurements.

Contribution

It introduces a scalable, multiplexed control architecture for surface-code quantum computing with fixed-frequency transmons, avoiding unwanted interactions.

Findings

Enables spatial multiplexing of control signals.

Pipelined stabilizer measurement improves efficiency.

Avoids second-order transmon interactions except for controlled-phase gates.

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.