Speaker: Eduardo Lee
Affiliation: Departamento de Física de la Materia Condensada and Condesed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid
Date: Monday, 25 May 2026 at 12:00
Location: Seminar Room, Serrano 121 (CFMAC)
We implement a gate-tunable transmon (gatemon) qubit based on an InAs nanowire
Josephson junction and identify distinct features in its microwave spectra that provide clear
evidence of ultrastrong light–matter hybridization with a probing resonator [1]. These
signatures include deviations of the measured anticrossing from the predictions of the
Jaynes–Cummings model. Furthermore, we observe photon-number-dependent transitions
whose energies deviate markedly from the JC ladder expected in the strong coupling limit.
We interpret these observations using extended theoretical models that incorporate both
counter-rotating interaction terms and the multilevel, non-conventionally anharmonic
structure of the gatemon. Beyond establishing USC, we achieve time-resolved coherent
control of the gatemon. We extract relaxation and decoherence times that are comparable to
those of gatemons operating outside the USC regime, suggesting that coherence is not
predominantly limited by the enhanced Purcell losses expected in this limit. These results
establish hybrid semiconductor-superconductor circuits as a viable platform for exploring
time-resolved quantum dynamics and new device concepts in the ultrastrong coupling
regime.
[1] I. Casal Iglesias et al., arXiv:2603.19438