Optimization of Floquet fluxonium qubits with commensurable two-tone drives

TL;DR

This paper investigates how two-tone Floquet drives can enhance the coherence and control of fluxonium qubits, offering more tunability and improved phase gate performance through theoretical and numerical analysis.

Contribution

It introduces a novel two-tone drive scheme for fluxonium qubits, demonstrating increased coherence time tunability and improved phase gate implementation over single-tone drives.

Findings

Two-tone drives create higher and wider peaks of dephasing time.

Optimal drive parameters are identified via perturbation theory and numerical methods.

Second commensurable tone improves phase gate performance.

Abstract

Protecting superconducting qubits from low-frequency noise by operating them on dynamical sweet-spot manifolds has proven to be a promising setup, theoretically as well as experimentally . These dynamical sweet spots are induced by an externally applied Floquet drive, and various drive forms have been studied in different types of qubits. In this work we study the effects of using two-tone drives on the applied magnetic flux of the form $\phi_{ac}(t)=\phi_m\cos(m\omega_\mathrm{d} t)+\phi_n\cos(n\omega_\mathrm{d} t+\varphi)$, where $m,n \in \mathbb{N}_{>0}$, on the coherence times of fluxonium qubits. The optimal drive parameters are found through analysis using perturbation theory and numerical calculations. We show that this type of drive allows for more tunability of the quasi-energy spectrum, creating higher and wider peaks of the dephasing time without affecting the relaxation times too strongly. Further we show that the second commensurable drive tone can be used to implement an improved phase gate compared to implementations with a single tone, supported by Monte Carlo simulations.