Two-body Wigner molecularization in asymmetric quantum dot spin qubits

TL;DR

This paper investigates how anisotropic confinement potentials in quantum dots enhance Coulomb-driven Wigner molecule formation, impacting spin qubit performance by suppressing exchange interactions and complicating readout mechanisms.

Contribution

It provides analytical and numerical analysis of two-particle states in anisotropic quantum dots, revealing the exponential suppression of the singlet-triplet gap due to molecularization effects.

Findings

Anisotropy significantly enhances Wigner molecule formation.

The singlet-triplet gap decreases exponentially with anisotropy.

Molecularization hampers Pauli spin blockade and reduces exchange interactions.

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.