Fast fluxonium readout with photon pumping and bath engineering

Circuit quantum electrodynamics with fluxonium qubits, a leading platform for quantum computation, continues to face the key challenge of achieving rapid and high-fidelity qubit readout. In this work, we propose an innovative, experimentally feasible readout scheme that relies on photon pumping. The geometric pumping transfers energy between an external periodic flux drive and resonant photonic output states via a higher-order filter, with the direction of energy transfer determined by the fluxonium qubit's basis state. Using Floquet adiabatic perturbation theory, we show that when initialized near a Floquet eigenstate, the qubit remains nearly perfectly confined to a single Floquet band throughout the pumping cycle. By filtering out the leakage transition while preserving the qubit transition frequency, we investigate the possibility of improving the readout process while maintaining the robustness central to quantum geometry. Furthermore, as the large photon numbers and ultra-strong coupling are desirable for readout with geometric pumping to make sure the qubit does not become highly entangled during readout, our scheme enables multiple photon frequencies to simultaneously measure the qubit while maintaining the high purity of the qubit subspace. We comment on the possibility of using this readout scheme to pave the way for fast, high-fidelity readout in future quantum computing applications.