Fluxonium as a control qubit for bosonic quantum information (part II)

Bosonic codes in superconducting resonators are a hardware-efficient avenue for quantum error correction and benefit from favorable error hierarchies provided by long-lived cavities compared to typical superconducting qubits. The required coupling to an ancillary control qubit, however, can negate these benefits by inducing highly detrimental effects such as excess decoherence and undesired nonlinearities. An important question is thus whether a cavity-qubit coupling can be realized that offers readout and control capabilities without spoiling the cavity.  Here, to complement the results of part 1 of this talk, we use the predictability of the resonator’s inherited nonlinearities to show numerically that the fluxonium can reach cavity-coupling regimes that eliminate undesirable cavity nonlinearities.  We present our work towards experimentally realizing a system with a vanishing cavity-self kerr.  We plan to incorporate this almost-purely dispersive interaction in a system with long coherence to achieve a bosonic memory with a low error rate.  These results demonstrate the potential of the fluxonium as a high-performance bosonic control qubit for superconducting cavities.