Magnetic Phases of Bilayer Quantum-Dot Hubbard Model Plaquettes

TL;DR

This paper explores the magnetic phases in a bilayer quantum dot Hubbard model, revealing diverse magnetic states and phase diagrams influenced by Coulomb interactions, with implications for quantum simulation and material design.

Contribution

It introduces a detailed phase diagram for bilayer quantum dot systems with long-range Coulomb interactions, highlighting complex magnetic phases and their dependence on interaction strengths.

Findings

Multiple magnetic phases including ferromagnetic and antiferromagnetic states were identified.

The phase diagram shows how inter- and intra-layer Coulomb interactions influence magnetic order.

Predictions include distinct behaviors in electron, hole, and electron-hole bilayer systems.

Abstract

It has been demonstrated that small plaquettes of quantum dot spin qubits are capable of simulating condensed matter phenomena which arise from the Hubbard model, such as the collective Coulomb blockade and Nagaoka ferromagnetism. Motivated by recent materials developments, we investigate a bilayer arrangement of quantum dots with four dots in each layer which exhibits a complex ground state behavior. We find using a generalized Hubbard model with long-range Coulomb interactions, several distinct magnetic phases occur as the Coulomb interaction strength is varied, with possible ground states that are ferromagnetic, antiferromagnetic, or having both one antiferromagnetic and one ferromagnetic layer. We map out the full phase diagram of the system as it depends on the inter- and intra-layer Coulomb interaction strengths, and find that for a single layer, a similar but simpler effect occurs. We also predict interesting contrasts among electron, hole, and electron-hole bilayer systems arising from complex correlation physics. Observing the predicted magnetic configuration in already-existing few-dot semiconductor bilayer structures could prove to be an important assessment of current experimental quantum dot devices, particularly in the context of spin-qubit-based analog quantum simulations.