Extending quantum coherence lifetimes in nonadiabatic dissipative molecular systems with chirped pulses.

Quantum coherences play a central role in a broad range of fields, including functional energy materials, biological systems, and molecular quantum information science. Coherences encode critical information about the phase and dynamics of a system, and their interaction with its environment. Particularly, the ultrafast charge transfer process between electron donor and acceptor species in functional energy materials is influenced by vibronic coherences. A key limitation arises from the dephasing of coherences due to dissipation, causing loss of information and limiting applications of molecular systems. Extending and controlling coherence lifetimes would enable the rational design of smarter materials with optimised properties. Here we introduce a novel idea using chirped excitations as a pathway to extend quantum coherence lifetimes, enhancing their robustness against dissipation. A detailed analysis of the light-induced molecular quantum dynamics and wave packet evolution from first-principles models constructed at the donor-acceptor heterojunction of an organic photovoltaic blend is discussed. We demonstrate that tuning the chirp of the excitation pulse, vibronic coherence lifetimes can be extended up to the picosecond timescale. Chirped excitations also enable tunable spatial localisation of the induced wave packet, with localisation controlled by the chirp intensity. These effects are observed consistently across different donor-acceptor adducts selected from the molecular dynamics structure of the blend. Our results introduce a new degree of freedom for coherent control in molecular systems, offering a promising pathway toward the development of advanced functional energy materials and applications in molecular quantum information science.