Floquet-engineered fast SNAP gates in weakly coupled circuit-QED systems

TL;DR

This paper introduces a method to significantly speed up SNAP gates in weakly coupled circuit-QED systems by using Floquet engineering and optimal control, enabling high-fidelity operations in high-coherence cavities.

Contribution

The authors develop a Floquet-based protocol combined with optimal control to achieve ultra-fast, high-fidelity SNAP gates in weakly coupled superconducting cavity-transmon systems, surpassing traditional speed limits.

Findings

Achieved SNAP gate speeds orders of magnitude faster than standard methods.

Demonstrated high fidelity in simulations of weakly coupled, high-coherence cavities.

Provided a theoretical framework explaining gate acceleration and decoherence.

Abstract

Superconducting cavities with high quality factors, coupled to a fixed-frequency transmon, provide a state-of-the-art platform for quantum information storage and manipulation. The commonly used selective number-dependent arbitrary phase (SNAP) gate faces significant challenges in ultra-high-coherence cavities, where the weak dispersive shifts necessary for preserving high coherence typically result in prolonged gate times. Here, we propose a protocol to achieve high-fidelity SNAP gates that are orders of magnitude faster than the standard implementation, surpassing the speed limit set by the bare dispersive shift. We achieve this enhancement by dynamically amplifying the dispersive coupling via sideband interactions, followed by quantum optimal control on the Floquet-engineered system. We also present a unified perturbation theory that explains both the gate acceleration and the associated benign drive-induced decoherence, corroborated by Floquet-Markov simulations. These results pave the way for the experimental realization of high-fidelity, selective control of weakly coupled, high-coherence cavities, and expanding the scope of optimal control techniques to a broader class of Floquet quantum systems.