Optimizing fluxonium readout fidelity and non-demolition character using quantum optimal control

The heavy fluxonium qubit has recently received significant attention due to its long coherence time and high-fidelity quantum gates. However, these properties typically lead to a small dispersive shift making standard readout approaches slow and error-prone. Flux tuning the fluxonium can increase its dispersive shift but leads to a loss of QNDness due to the presence of resonances with the resonator transitions. Here, we use an open-system quantum optimal control approach to optimize this tradeoff while considering the full quantum system of a fluxonium coupled to its dissipative readout resonator. We combine gradient-based and gradient-free optimisations to investigate the full control parameter space and find novel time dependent charge-drive and flux-drive based control schemes that improve the duration and fidelity of fluxonium readout while preserving its QND character. We focus on developing experimentally realistic controls by using comprehensive numerical simulations and exploring protocols that would be straightforward to calibrate on an actual quantum device.

This work is supported by a collaboration between the US DOE and other Agencies. This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Quantum Systems Accelerator. Additional support is acknowledged from NSERC, the Canada First Research Excellence Fund, the Ministère de l’Économie et de l’Innovation du Québec.