Basis-independent coherence and quantum correlations in two dipole-dipole-coupled electrons in double quantum-dot molecules

This paper investigates how the interplay of four key Hamiltonian parameters—inter-dot tunneling (Γ), energy detuning (ε), Coulomb repulsion (J), and dipole-dipole coupling (K)—governs the thermal stability of quantum resources in a system of two dipole-dipole-coupled electrons confined in spatially separated double quantum-dot (DQD) molecules. The authors aim to identify which parameters protect or destroy quantum coherence and correlations as temperature increases.

The researchers model the system as two DQD molecules, each hosting a single electron. They analyze the thermal dynamics of the Gibbs state by calculating several metrics: localized and collective coherence, Bures distance entanglement, local quantum uncertainty (LQU), and local quantum Fisher information (LQFI). By varying the Hamiltonian parameters, they map how these quantum resources evolve from zero temperature up to T=10 (in energy units), providing a comprehensive view of how structural design choices impact the robustness of quantum information in solid-state architectures.

The study reveals that dipole-dipole coupling (K) is the most critical parameter for preserving quantum resources; it effectively extends the temperature range of entanglement and enhances collective coherence. Coulomb repulsion (J) acts as a reinforcing mechanism, projecting the system into a more stable entangled subspace. Conversely, while inter-dot tunneling (Γ) enhances localized coherence at low temperatures, it is detrimental to collective coherence and entanglement. Similarly, energy detuning (ε) promotes localized coherence but paradoxically accelerates the decay of entanglement and nonclassical correlations, effectively quenching the system's metrological utility.

As semiconductor quantum-dot molecules are a leading platform for charge-qubit implementations, understanding the thermal stability of these systems is essential for practical quantum computing. This work provides a clear hierarchy of parameter influence, helping designers of Si/SiGe-based quantum devices optimize their architectures to maintain quantum correlations at higher operating temperatures.