Predicting measurement-induced state transitions in fluxonium readout.

The dispersive readout scheme facilitates quantum non-demolition measurement of superconducting qubits. However, while an increased readout power can shorten the integration time and reduce the state discrimination error, it can promote qubit transitions into higher noncomputational states, destroying the quantum non-demolition character of the readout protocol and complicating qubit reset. In this talk, we discuss the physics behind such measurement-induced state transitions (MIST) in a superconducting fluxonium circuit during resonator ring-up. Our explanation of MIST for fluxonium is based on multi-photon resonances between energy levels of the interacting qubit-resonator system corresponding to different qubit states. The ability to predict the onset of MIST can aid the optimization of fluxonium parameters to realize high-fidelity qubit readout.