Engineering, control and longitudinal readout of Floquet qubits

TL;DR

This paper explores the control and readout of Floquet qubits using many-mode Floquet theory, demonstrating enhanced robustness and a faster measurement protocol for time-periodic Hamiltonian systems.

Contribution

It introduces a longitudinal readout method for Floquet qubits and applies many-mode Floquet theory to improve qubit control and measurement speed.

Findings

Floquet states provide enhanced dynamical protection.

The proposed readout protocol speeds up measurement times.

Analytical framework applicable to multi-tone driven Hamiltonians.

Abstract

Properties of time-periodic Hamiltonians can be exploited to increase the dephasing time of qubits and to design protected one and two-qubit gates. Recently, Huang et al. [Phys. Rev. Applied 15, 034065 (2021)] have shown that time-dependent Floquet states offer a manifold of working points with dynamical protection larger than the few usual static sweet spots. Here, we use the framework of many-mode Floquet theory to describe approaches to robustly control Floquet qubits in the presence of multiple drive tones. Following the same approach, we introduce a longitudinal readout protocol to measure the Floquet qubit without the need of first adiabatically mapping back the Floquet states to the static qubit states, which results in a significant speedup in the measurement time of the Floquet qubit. The analytical approach developed here can be applied to any Hamiltonian involving a small number of distinct drive tones, typically the study of standard parametric gates for qubits outside of the rotating-wave approximation.