Microscopic Origin of the Effective Spin-Spin Interaction in a Semiconductor Quantum Dot Ensemble

Area of Science:

• Condensed Matter Physics
• Quantum Information Science
• Materials Science

Background:

• Understanding electron spin interactions in quantum dots (QDs) is crucial for quantum computing.
• Previous models struggled to explain the observed long-range effective interactions between spins in QD ensembles.

Purpose of the Study:

• To develop a microscopic model explaining the origin of long-range effective interactions between electron spins in singly charged QDs.
• To investigate the role of the wetting layer in mediating these spin-spin interactions.

Main Methods:

• Utilized Wilson's numerical renormalization group (NRG) to calculate the spin-spin interaction.
• Incorporated growth-induced wetting layer properties and particle-hole asymmetry.
• Employed semiclassical simulations for large QD ensembles using NRG results.

Main Results:

• Identified an unexpected antiferromagnetic Heisenberg coupling at very short inter-QD distances.
• Attributed this short-range interaction to particle-hole asymmetry in the wetting layer band at low filling.
• Successfully reproduced experimentally observed phase shifts in coherent spin dynamics.

Conclusions:

• The microscopic model successfully explains the origin of inter-QD electron spin-spin interactions.
• The wetting layer's properties, particularly its asymmetry, are key to understanding these interactions.
• This work resolves a long-standing open problem in quantum dot spin dynamics.