Hardware-Efficient Microwave-Activated Tunable Coupling Between Superconducting Qubits

TL;DR

This paper demonstrates a microwave-driven, tunable $ZZ$ interaction between fixed-frequency transmon qubits, enabling high-fidelity quantum gates with reduced control complexity and noise, suitable for scalable quantum processors.

Contribution

It introduces a novel method for tunable qubit interactions using off-resonant driving, eliminating the need for flux-tunable elements and enhancing scalability.

Findings

Achieved tunable $ZZ$ interaction over an order of magnitude larger than static coupling.

Implemented a controlled phase (CZ) gate with 99.43% fidelity.

Interaction is resilient to microwave crosstalk and adaptable to large quantum processors.

Abstract

Generating high-fidelity, tunable entanglement between qubits is crucial for realizing gate-based quantum computation. In superconducting circuits, tunable interactions are often implemented using flux-tunable qubits or coupling elements, adding control complexity and noise sources. Here, we realize a tunable $ZZ$ interaction between two transmon qubits with fixed frequencies and fixed coupling, induced by driving both transmons off-resonantly. We show tunable coupling over one order of magnitude larger than the static coupling, and change the sign of the interaction, enabling cancellation of the idle coupling. Further, this interaction is amenable to large quantum processors: the drive frequency can be flexibly chosen to avoid spurious transitions, and because both transmons are driven, it is resilient to microwave crosstalk. We apply this interaction to implement a controlled phase (CZ) gate with a gate fidelity of $99.43(1)\%$ as measured by cycle benchmarking, and we find the fidelity is limited by incoherent errors.