Spin-Valley Protected Kramers Pair in Bilayer Graphene

Abstract

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 two-fold 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 both quantum numbers. Here, we fabricate a tunable QD device in Bernal BLG and measure a spin-valley relaxation time for the Kramers states of $38\mathrm{s}$, which is two orders of magnitude longer than the $0.4\mathrm{s}$ 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.

Supplementary Information is included in the .pdf

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Cited by in corpus (7)

• Spin-Valley Protected Kramers Pair in Bilayer Graphene
• Tunable spin-orbit splitting in bilayer graphene/WSe${}_2$ quantum devices
• Phonon-limited valley life times in single-particle bilayer graphene quantum dots
• The role of antisymmetric orbitals and electron-electron interactions on the two-particle spin and valley blockade in graphene double quantum dots
• Increasing the proximity induced spin-orbit coupling in bilayer graphene/WSe${}_2$ heterostructures with pressure
• Spin-photon coupling using circular double quantum dots
• Unprecedented Spin-Lifetime of Itinerant Electrons in Natural Graphite Crystals