Floquet-engineered enhancement of coherence times in a driven fluxonium qubit

TL;DR

This paper demonstrates that Floquet engineering can significantly enhance the coherence times of a fluxonium qubit by creating dynamical sweet spots insensitive to flux noise, achieving a 40-fold improvement.

Contribution

The study introduces a Floquet-based method to identify and utilize dynamical sweet spots for fluxonium qubits, improving coherence times beyond static biasing.

Findings

40-fold increase in coherence times at the dynamical sweet spot

Insensitivity to flux and amplitude noise at the optimal working point

Flexible control of qubit parameters via Floquet engineering

Abstract

We use the quasienergy structure that emerges when a fluxonium superconducting circuit is driven periodically to encode quantum information with dynamically induced flux-insensitive sweet spots. The framework of Floquet theory provides an intuitive description of these high-coherence working points located away from the half-flux symmetry point of the undriven qubit. This approach offers flexibility in choosing the flux bias point and the energy of the logical qubit states as shown in [\textit{Huang et al., 2020}]. We characterize the response of the system to noise in the modulation amplitude and DC flux bias, and experimentally demonstrate an optimal working point which is simultaneously insensitive against fluctuations in both. We observe a 40-fold enhancement of the qubit coherence times measured with Ramsey-type interferometry at the dynamical sweet spot compared with static operation at the same bias point.