Talk by Julien Renard
Graphene superconducting circuits: from Josephson junctions to qubits and functional devices
Talk by Julien Renard, Institut Néel, CNRS, Université Grenoble Alpes, France
ABSTRACT
About 10 years ago, it was shown that semiconductor-based Josephson junctions could be integrated into functional superconducting devices such as qubits [1]. Among other characteristics that I will discuss during this seminar, such junctions can be tuned with a simple electric field effect. These original demonstrations were made with InAs nanowires but, in the last 10 years, many other platforms have been used, for instance two-dimensional electron gases.
In my group, we use graphene to fabricate high-quality Josephson junctions. We have achieved the first realization of a gate-tunable Josephson parametric amplifier with such junctions [2]. More recently, we focused on the properties of qubits. While the performances are still very far from that of qubits made with tunnel junctions, we showed that the peculiar characteristics of the junctions lead to original effects, for example, in terms of anharmonicity [3,4]. Finally, I will discuss our ongoing work in this field, leveraging the gate tunability of the Josephson junctions to demonstrate three-wave mixing amplification but also focusing on the intrinsic losses of such junctions or exploring the possibility of realizing a protected qubit [5].
[1] T. W. Larsen et al., Phys. Rev. Lett. 115, 127001 (2015) and G. De Lange et al. Phys. Rev. Lett. 115, 127002 (2015)
[2] G. Butseraen et al., A gate-tunable graphene Josephson parametric amplifier, Nature Nanotech. 17, 1153 (2022)
[3] S. Messelot et al., Direct Measurement of a sin(2phi) Current Phase Relation in a Graphene Superconducting Quantum Interference Device, Phys. Rev. Lett. 133, 106001 (2024)
[4] N. Aparicio et al., Gate-tunable spectrum and charge dispersion mitigation in a graphene superconducting qubit, Phys. Rev. Lett. 135, 266001 (2025)
[5] S. Messelot et al., Coherence limits in interference-based cos (2φ) qubits, arXiv:2601.10209, Phys. Rev. Appl, in press (2026)
Host: Jesper Nygård, NBI