Experimental mitigation of readout-induced leakage by Floquet-based optimization of the readout frequency

Readout-induced spurious excitations impose an ultimate limit on the speed and accuracy of qubit readout in superconducting circuits. In particular, readout induced leakage out of the computational subspace introduces correlated errors, which present a significant challenge for applications such as quantum error correction. In this work, we first characterize readout-induced leakage in a Purcell-protected qubit embedded within a multi-mode circuit. We then investigate the underlying physical dynamics responsible for the leakage and show that parasitic multiphoton excitations are accurately predicted by the Floquet steady-state simulation of the physical system. Finally, we demonstrate that optimizing the readout frequency based on these Floquet steady-state simulations can significantly suppress readout-induced leakage, enhancing both speed and accuracy in qubit readout.