Extensible circuit-QED architecture via amplitude- and frequency-variable microwaves

TL;DR

This paper proposes an extensible circuit-QED architecture with tunable microwave-driven couplers, enabling high-fidelity two-qubit gates over a broad frequency range, and introduces a Floquet-theory-based framework for modeling and pulse shaping.

Contribution

It introduces a novel circuit-QED architecture with tunable microwave controls and develops a Floquet-theory-based method for modeling driven interactions and optimizing gate fidelity.

Findings

Achieves average gate fidelities above 99.9% for controlled-phase gates.

Demonstrates gate operation times between 50-120 ns.

Shows that the architecture allows for large drive-frequency bandwidths.

Abstract

We introduce a circuit-QED architecture combining fixed-frequency qubits and microwave-driven couplers. In the appropriate frame, the drive parameters appear as tunable knobs enabling selective two-qubit coupling and coherent-error suppression. We moreover introduce a set of controlled-phase gates based on drive-amplitude and drive-frequency modulation. We develop a theoretical framework based on Floquet theory to model microwave-activated interactions with time-dependent drive parameters, which we also use for pulse shaping. We perform numerical simulations of the gate fidelity for realistic circuit parameters, and discuss the impact of drive-induced decoherence. We estimate average gate fidelities beyond $99.9\%$ for all-microwave controlled-phase operations with gate times in the range $50-120\,\mathrm{ns}$. These two-qubit gates can operate over a large drive-frequency bandwidth and in a broad range of circuit parameters, thereby improving extensibility. We address the frequency allocation problem for this architecture using perturbation theory, demonstrating that qubit, coupler and drive frequencies can be chosen such that undesired static and driven interactions remain bounded in a multi-qubit device. Our numerical methods are useful for describing the time-evolution of driven systems in the adiabatic limit, and are applicable to a wide variety of circuit-QED setups.