Spin–valley protected Kramers pair in bilayer graphene
The intrinsic valley degree of freedom makes bilayer graphene (BLG) a unique platform for semiconductor qubits. The single-carrier quantum dot (QD) ground state exhibits a twofold degeneracy, where the two states that constitute a Kramers pair have opposite spin and valley quantum numbers. Because of the valley-dependent Berry curvature, an out-of-plane magnetic field breaks the time-reversal symmetry of this ground state and a qubit can be encoded in the spin-valley subspace. The Kramers states are protected against known spin- and valley-mixing mechanisms because mixing requires a simultaneous change of the two quantum numbers. Here, we fabricate a tunable QD device in Bernal BLG and measure a spin-valley relaxation time for the Kramers states of 38 s at 30 mK, which is two orders of magnitude longer than the 0.4 s measured for purely spin-blocked states. We also show that the intrinsic Kane-Mele spin-orbit splitting enables a Kramers doublet single-shot readout even at zero magnetic field with a fidelity above 99%. If these long-lived Kramers states also possess long coherence times and can be effectively manipulated, electrostatically defined QDs in BLG may serve as long-lived semiconductor qubits, extending beyond the spin qubit paradigm.
Authors
- Hadrien Duprez (ORCID: https://orcid.org/0000-0003-0506-126X)
- Artem O. Denisov (ORCID: https://orcid.org/0000-0001-9095-1579)
- Max J. Ruckriegel (ORCID: https://orcid.org/0000-0002-4776-699X)
- Christoph Adam (ORCID: https://orcid.org/0000-0001-9408-6439)
- Takashi Taniguchi (ORCID: https://orcid.org/0000-0002-1467-3105)
- Kenji Watanabe (ORCID: https://orcid.org/0000-0003-3701-8119)
- Thomas Ihn (ORCID: https://orcid.org/0000-0002-5587-6953)
- Chuyao Tong (ORCID: https://orcid.org/0000-0003-4947-6002)
- W. Huang (ORCID: https://orcid.org/0000-0001-9996-6371)
- Michele Masseroni (ORCID: https://orcid.org/0000-0003-1663-8239)
- K. Ensslin (ORCID: https://orcid.org/0000-0001-7007-6949)
- Jonas D. Gerber (ORCID: https://orcid.org/0000-0002-4164-8765)
- Solenn Cances
- Veronika Reckova
Institutions
- Solid State Physics Laboratory (IN)
- National Institute for Materials Science (JP)
- ETH Zurich (CH)
Publication Details
- Journal
- Nature Nanotechnology
- Published
- 2025-02-10
- DOI
- https://doi.org/10.1038/s41565-025-01858-8
- Citations
- 18
- Primary Topic
- Quantum and electron transport phenomena
- Type
- article
- Field-Weighted Citation Impact
- 22.44
Funders
- National Science Foundation
- Graphene Flagship
- Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
- Eidgenössische Technische Hochschule Zürich
- Horizon 2020 Framework Programme
- Japan Society for the Promotion of Science
- National Center of Competence in Research Quantum Science and Technology
- H2020 European Research Council
- HORIZON EUROPE European Innovation Council