Laser-field detuning assisted optimization of valley dynamics in monolayer WSe2

Optimizing valley dynamics serves as an effective tool for facilitating the coherent control within the framework of two-dimensional semiconductors. In this study, we develop a comprehensive model that encompasses both intravalley and intervalley exciton channels in monolayer WSe2, and simultaneously takes the light-matter interaction into account. This model allows us to investigate the optimal control of valley dynamics starting from an initial coherent excitonic state. Drawing upon the quantum speed limit (QSL) theory, we propose two optimal control schemes with the goal of reducing the evolution time required for valley dynamics to reach the final state, and of enhancing the evolution speed over a period of time. We emphasize that the implementation of dynamical optimization is associated with the detuning difference, the variance in exciton-laser field detunings between the K and K' ' valleys, dictated by the optical excitation mode and magnetically induced valley splitting. Specifically, to minimize the evolution time, we find that a small detuning difference drives the actual dynamical path to converge toward the geodesic length from the initial state to final state, enabling the system to evolve in the shortest time. In particular, in the presence of valley coherence, the actual evolution time closely aligns with the calculated QSL time, facilitating high-fidelity quantum system evolution. Conversely, we illustrate a remarkable enhancement in the evolution speed of valley dynamics by using a large detuning difference, which induces emerging valley polarization even without initial polarization. Our work has important theoretical implications for facilitating coherent valley manipulations, and could also serve as a guide for searching optimal evolution path in relevant experiments.