Pauli Blockade of Tunable Two-Electron Spin and Valley States in Graphene Quantum Dots

TL;DR

This paper demonstrates Pauli blockade phenomena involving spin and valley states in tunable bilayer graphene quantum dots, revealing new control mechanisms for quantum information applications.

Contribution

It reports the first observation of combined spin and valley Pauli blockade in bilayer graphene quantum dots with tunable ground states.

Findings

Observation of valley blockade with spin-triplet--valley-singlet ground state.

Robust spin blockade with spin-singlet--valley-triplet ground state.

Gate and magnetic field tuning switches ground states and selection rules.

Abstract

Pauli blockade mechanisms -- whereby carrier transport through quantum dots is blocked due to selection rules even when energetically allowed -- are a direct manifestation of the Pauli exclusion principle, as well as a key mechanism for manipulating and reading out spin qubits. Pauli spin blockade is well established for systems such as GaAs QDs, but is to be further explored for systems with additional degrees of freedom, such as the valley quantum numbers in carbon-based materials or silicon. Here we report experiments on coupled bilayer graphene double quantum dots, in which the spin and valley states are precisely controlled, enabling the observation of the two-electron combined blockade physics. We demonstrate that the doubly occupied single dot switches between two different ground states with gate and magnetic-field tuning, allowing for the switching of selection rules: with a spin-triplet--valley-singlet ground state, valley-blockade is observed; and with the spin-singlet--valley-triplet ground state, robust spin blockade is shown.