Gate-tunable transmon qubits are based on quantum conductors used as weak links within hybrid Josephson junctions. These gatemons have been implemented in just a handful of systems, all relying on extended conductors, namely epitaxial semiconductors or exfoliated graphene. Here we present the coherent control of a gatemon based on a single molecule, a one-dimensional carbon nanotube, which is integrated into a circuit quantum electrodynamics architecture. The measured qubit spectrum can be tuned with a gate voltage and reflects the quantum dot behaviour of the nanotube. Our ultraclean integration, using a hexagonal boron nitride substrate, results in record coherence times of 200ns for carbon nanotube-based qubits. Furthermore, we investigate its decoherence mechanisms, thus revealing a strong gate dependence and identifying charge noise as a limiting factor. On top of positioning carbon nanotubes as contenders for future quantum technologies, our work paves the way for studying microscopic fermionic processes in low-dimensional quantum conductors.
@article{arxiv.2503.01978,
title = {The carbon nanotube gatemon qubit},
author = {H. Riechert and S. Annabi and A. Peugeot and H. Duprez and M. Hantute and K. Watanabe and T. Taniguchi and E. Arrighi and J. Griesmar and J. -D. Pillet and L. Bretheau},
journal= {arXiv preprint arXiv:2503.01978},
year = {2025}
}