Flux-Insensitive Fluxonium Qubit with Flux-Tunable Coupling

With its intrinsic charge noise protection and demonstrated long coherence times, a fluxonium qubit is a promising building block for quantum information processing in superconducting systems. In a fluxonium, the qubit Josephson junction is shunted by a large linear inductance which, in practice, is realized using a chain of Josephson junctions. In this study, we explore the limit of the fluxonium qubit when the value of shunt inductance is pushed to higher values, from roughly one hundred nanohenry (for a typical fluxonium device) to more than a microhenry. Such an order of magnitude increase in shunting inductance makes the 0-1 qubit transition nearly flux-insensitive, thereby substantially reducing the qubit dephasing due to flux noise. However, the transitions to and between higher, non-computational qubit states still remain flux-sensitive yielding a direct way to control coupling between the qubits with flux as a tunning knob while also maintaining the qubit protection from flux noise. In this talk, we report our progress towards experimental realization of a flux-insensitive fluxonium qubit.