Orthogonal frequency-division multiplexing for simultaneous gate operations on multiple qubits via a shared control line

TL;DR

This paper proposes an FDM-based microwave control scheme for simultaneous multi-qubit gate operations, addressing scalability challenges in quantum processors by reducing control line complexity and maintaining high fidelity.

Contribution

It introduces a novel frequency-division multiplexing approach with design guidelines for scalable, high-fidelity multi-qubit control using shared microwave lines.

Findings

Orthogonal microwave signals suppress interference between qubits.

Drive frequency spacing affects gate fidelity.

Design parameters like pulse length and number of signals are critical.

Abstract

The increasing number of qubits in quantum processors necessitates a corresponding increase in the number of control lines between the processor, which is typically operated at cryogenic temperatures, and external electronics. Scaling poses significant challenges in terms of the thermal loads, forming a major bottleneck in the realization of large-scale quantum computers. In this study, we analyze simultaneous gate operations on multiple qubits using microwaves transmitted via a single cable in a frequency-division multiplexing (FDM) scheme. By employing rectangular control microwave pulses, we reveal the contribution of drive frequency spacing to gate fidelity. Through theoretical and numerical analyses, we demonstrate that orthogonal and quasi-orthogonal microwave signals suppress interference in simultaneously driven qubits, thereby ensuring high gate fidelity. Additionally, we provide design guidelines for key parameters, including pulse length, number of multiplexed microwave signals, and rotation angle, to achieve precise qubit operations. Our findings enable a scalable FDM-based microwave control scheme suitable for quantum processors with a large number of qubits.