Protected Qubit Subspace within a Fluxonium Molecule

Qubits with inherent immunity to depolarization and pure dephasing processes are desirable for fault tolerant quantum processors, as both a complement and supplement to quantum error correction schemes. Such “protected” qubits in superconducting circuits have been proposed theoretically [1], and recently realized in the first experimental demonstration of the 0-π qubit [2]. The hunt for new species of protected qubits within the reach of current superconducting technologies is underway. Here we detail work towards a new flavour of protected qubit based on a fluxonium molecule circuit [3] using a non-traditional subspace which exhibits disjoint support and is to first order insensitive to flux noise. We present preliminary work towards realizing this protected qubit and detail its theoretical framework.

[1] A. Kitaev, https://arxiv.org/abs/cond-mat/0609441 (2006)
[2] A. Gyenis, P. S. Mundada, A. Di Paolo, T. Hazard, X. You, D. Schuster, J. Koch, A. Blais and A. A. Houck, https://arxiv.org/abs/1910.07542 (2020)
[3] 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, 03137 (2017)