Quantum Dynamics of Incoherently Driven Systems

D. C. Hutcgings

Suyesh Koyu, Timur V. Tscherbul

We present a theoretical study of quantum coherent dynamics in a three-level $\Lambda$ system driven by a thermal environment. By solving the nonsecular Bloch-Redfield master equations, we obtain analytical results for the ground-state population and coherence dynamics and classify the dynamical regimes of the incoherently driven $\Lambda$-system as underdamped and overdamped depending on whether the ratio $\Delta/[r f(p)]$ is greater or less than one, where $\Delta$ is the ground-state energy splitting, $r$ is the incoherent pumping rate, and $f(p)$ is a dimensionless function of the transition dipole alignment parameter $p$. In the underdamped regime, we observe long-lived coherent dynamics that lasts for $\tau_c\simeq 1/r$, even though the initial state of the $\Lambda$-system contains no coherences in the energy basis. In the overdampled regime for $p = 1$, we observe the emergence of coherent quasi-steady states with the lifetime $\tau_{c} = 1.34 (r/\Delta^{2})$, which have low von Neumann entropy compared to the conventional thermal states. Our results suggest that thermal excitations can enhance the lifetimes of initially created coherent superpositions, making thermal driving a potentially useful coherence-enhancing tool for quantum information science.

Suyesh Koyu, Timur V. Tscherbul

Xiang Ying Sun

Geoffrey L. Price, Baker, B. Mitchell, Palle E. T. Jørgensen +1 more

Suyesh Koyu, Timur V. Tscherbul

We present a theoretical study of quantum coherent dynamics of a three-level Λ-system driven by a thermal environment (such as blackbody radiation), which serves as an essential building block of photosynthetic light-harvesting models and quantum heat engines. By solving nonsecular Bloch–Redfield master equations, we obtain analytical results for the ground-state population and coherence dynamics and classify the dynamical regimes of the incoherently driven Λ-system as underdamped and overdamped depending on whether the ratio Δ/[rf(p)] is greater or less than one, where Δ is the ground-state energy splitting, r is the incoherent pumping rate, and f(p) is a function of the transition dipole alignment parameter p. In the underdamped regime, we observe long-lived coherent dynamics that lasts for τc ≃ 1/r, even though the initial state of the Λ-system contains no coherences in the energy basis. In the overdamped regime for p = 1, we observe the emergence of coherent quasi-steady states with the lifetime τc = 1.34(r/Δ2), which have a low von Neumann entropy compared to conventional thermal states. We propose an experimental scenario for observing noise-induced coherent dynamics in metastable He* atoms driven by x-polarized incoherent light. Our results suggest that thermal excitations can generate experimentally observable long-lived quantum coherent dynamics in the ground-state subspace of atomic and molecular Λ-systems in the absence of coherent driving.