A composite Floquet flux qubit with long coherence*

High-coherence qubits, which can store and manipulate quantum states for long times with low error rates, are an important building block for eventual fault-tolerant quantum computers. We propose a superconducting qubit architecture that uses Floquet physics to achieve long coherence times for bit and phase flip errors, leaving erasures as the dominant (albeit still small) type of logical error. Using a periodic flux drive, we modify the spectrum of a static fluxonium molecule at half flux and obtain computational eigenstates which have two key properties: bit flips minimized by largely disjoint wavefunctions, and dephasing which vanishes at second order in perturbation theory for flux noise. We estimate the rate of all three error types with numerical simulations. Our results extend prior work on both dual-rail qubits and Floquet single-fluxonium qubits, and indicate that AC-driven qubits may be able to outperform their static counterparts.