Discovery of energy landscapes towards optimized quantum transport: Environmental effects and long-range tunneling

Carrier transport in quantum networks is governed by a variety of factors, including network dimensionality and connectivity, on-site energies, couplings between sites and whether they are short- or long-range, leakage processes, and environmental effects. In this work, we identify classes of quasi-one-dimensional chains with energy profiles that optimize carrier transport under such influences. Specifically, we optimize on-site energies using Optax’s optimistic gradient descent and AdaMax algorithms, enabled by the JAX automatic differentiation framework. Focusing on nonequilibrium steady-state transport, we study the system’s behavior under combined unitary and nonunitary (dephasing and dissipative) effects using the Lindblad quantum master equation. After validating our optimization scheme on short chains, we extend the study to larger systems where we identify systematic patterns in energy profiles. Our analysis reveals that different types of energy landscapes enhance transport, depending on whether inter-site tunneling couplings in the chain are short- or long-range, the existence of environmental interactions, and the temperature of the environment. Our classification and insights of optimal energy landscapes offer guidance for designing efficient transport systems for electronic, photovoltaic and quantum communication applications.

💡 Research Summary

This paper investigates how to engineer on‑site energy landscapes in quasi‑one‑dimensional quantum chains so that carrier transport is maximized under realistic unitary and dissipative influences. The authors model the chain with a tight‑binding Hamiltonian H = ∑ₙεₙ|n⟩⟨n| + ∑_{n≠m}J|n‑m||n⟩⟨m|, where the tunneling amplitude follows a power‑law J|n‑m| = J_max |n‑m|^{‑α}. By choosing α = 3 they obtain a short‑range (nearest‑neighbor) coupling, while α = 1 yields an all‑to‑all long‑range coupling.

Two open‑quantum‑system (OQS) models are considered. Model I implements local pure dephasing on each site with Lindblad operators Lₙ = |n⟩⟨n| and a uniform rate Γ. This corresponds to an effectively infinite‑temperature bath and reproduces the well‑known environment‑assisted quantum transport (ENAQT) peak when Γ/J_max ≈ 1. Model II treats a finite‑temperature bosonic environment in the global (energy‑eigenbasis) Lindblad form. Transition rates W_{ab}=Γ₀|ω_{ab}|