Experimental Investigation of a Protected Qubit Subspace Within a Fluxonium Molecule*

Protection against depolarization and pure dephasing processes is desirable for long coherence times in qubits. The disjoint support of the logical wavefunctions and sweet spots in the qubit energy landscape protect against spontaneous qubit relaxation and pure dephasing, respectively. We employ a fluxonium molecule [1] circuit to engineer protection against noise within a novel subspace. This subspace has disjoint support of the logical wavefunctions and a sweet spot in the energy spectrum. Here we present our recent progress, including working towards accessing full flux quanta along both control axes.

[1] A. Kou, W. C. Smith, U. Vool, R. T. Brierley, H. Meier, L. Frunzio, S. M. Girvin, L. I. Glazman, and M. H. Devoret, Phys. Rev. X 7, 031037 (2017)