Fluxonium Qubit Readout Using Its Josephson Junction Array Mode

To achieve non-demolition, high-fidelity measurement of a fluxonium qubit, dispersive readout using a coplanar waveguide (CPW) resonator is commonly employed. However, this approach has two major drawbacks: it requires a large footprint, limiting circuit design flexibility, and introduces an additional degree of freedom that couples to the fluxonium qubit, forming a complex composite system. These challenges make CPW-based readout a potential bottleneck for scalable fluxonium-based quantum processors.

As an alternative, we propose a dispersive readout approach that exploits an internal degree of freedom of the fluxonium qubit, namely its Josephson junction array mode. This array mode exhibits strong coupling to the qubit, enabling a large dispersive shift [1]. Importantly, this method eliminates the need for an external resonator mode, reducing both footprint and system complexity. In this talk, we present our theoretical framework for array-mode-based readout and share preliminary experimental results.

[1] G. Viola et al., Phys. Rev. B 92, 224511 (2015).