Two-body Wigner molecularization in asymmetric quantum dot spin qubits

Abstract

Coulomb interactions strongly influence the spectrum and the wave functions of few electrons or holes confined in a quantum dot. In particular, when the confinement potential is not too strong, the Coulomb repulsion triggers the formation of a correlated state, the Wigner molecule, where the particles tend to split apart. We show that the anisotropy of the confinement potential strongly enhances the molecularization process and affects the performances of quantum-dot systems used as spin qubits. Relying on analytical and numerical solutions of the two-particle problem -both in a simplified single-band approximation and in realistic setups -we highlight the exponential suppression of the singlet-triplet gap with increasing anisotropy. We compare the molecularization effects in different semiconductor materials and discuss how they specifically hamper Pauli spin blockade readout and reduce the exchange interactions in two-qubit gates.

Non-reciprocal Pauli Spin Blockade in a Silicon Double Quantum Dot

“…Additionally, spin, valley, and orbital degrees of freedom may all be mixed on a wide energy range by spin-orbit and valley-orbit couplings, which together with Coulomb interactions provide efficient paths for decoherence. In particular, it has been shown in [49] that anisotropic QDs such as the ones characterised in this work are prone to Wigner-like localization: The electrons split apart in the charged dots due to Coulomb repulsion, which results in a significant compression of the energy spectrum [29] and mixing of the different degrees of freedom in the presence of spin-orbit and valley-orbit coupling mechanisms [50][51][52]. Although the observed γ Dq at the anti-crossing is large, one may expect a reduction away from the anticrossing where the energy difference of intradot transitions is ε-independent, thus encouraging coherent EDSR experiments for electron spins in silicon corner dots.…”