We report observations of transitions between excited states in the Jaynes-Cummings ladder of circuit quantum electrodynamics with electron spins (spin circuit QED). We show that unexplained features in recent experimental work correspond to such transitions and present an input-output framework that includes these effects. In new experiments, we first reproduce previous observations and then reveal both excited-state transitions and multiphoton transitions by increasing the probe power and using two-tone spectroscopy. This ability to probe the Jaynes-Cummings ladder is enabled by improvements in the coupling-to-decoherence ratio, and shows an increase in the maturity of spin circuit QED as an interesting platform for studying quantum phenomena.
@article{arxiv.2203.05668,
title = {Probing the Jaynes-Cummings Ladder with Spin Circuit Quantum Electrodynamics},
author = {Tobias Bonsen and Patrick Harvey-Collard and Maximilian Russ and Jurgen Dijkema and Amir Sammak and Giordano Scappucci and Lieven M. K. Vandersypen},
journal= {arXiv preprint arXiv:2203.05668},
year = {2023}
}