Abstract
A comprehensive description of molecular electron transfer reactions is essential for our understanding of fundamental phenomena in bio-energetics and molecular electronics. Experimental studies of molecular systems in condensed-phase environments, however, face difficulties to independently control the parameters that govern the transfer mechanism with high precision. We show that trapped-ion experiments instead allow to reproduce and continuously connect vastly different regimes of molecular charge transfer through precise tuning of, e.g., phonon temperature, electron-phonon interactions, and electronic couplings. Such a setting allows not only to reproduce widely-used transport models, such as Marcus theory. It also provides access to transfer regimes that are unattainable for molecular experiments, while controlling and measuring the relevant observables on the level of individual quanta. Our numerical simulations predict an unconventional quantum transfer regime, featuring a transition from quantum adiabatic- to resonance-assisted transfer as a function of the donor-acceptor energy gap, that can be reached by increasing the electronic coupling at low temperatures. Trapped ion-based quantum simulations thus promise to enhance our microscopic understanding of molecular electron transfer processes, and may help to reveal efficient design principles for synthetic devices.
Highlights
Molecular electron-transfer (ET) reactions are the fundamental steps in many chemical and biological processes [1,2,3,4,5,6]
Our numerical simulations predict an unconventional quantum transfer regime, featuring a transition from quantum adiabatic to resonance-assisted transfer as a function of the donor-acceptor energy gap, which can be reached by increasing the electronic coupling at low temperatures
More flexibility in tuning the electronic transfer properties of the system is offered by engineered electronic coupling between different ions with a tunable interaction range, which can be controlled via an effective spin-spin coupling using additional motional modes [58,59]
Summary
Molecular electron-transfer (ET) reactions are the fundamental steps in many chemical and biological processes [1,2,3,4,5,6]. An experimental platform that offers precisely this kind of continuous tunability consists of arrays of electrostatically interacting ions trapped by harmonic external potentials [21,22,23,24], with an accuracy of individual parameter control evidenced by their performance among the best atomic clocks [25] These systems are currently considered among the leading architectures for the realization of quantum simulators and computers [22,23,24,26,27]. We predict the crossover from conventional nonadiabatic molecular ET to a quantum transfer regime where rates are limited by phonon lifetimes in the normal regime and heavily modulated by resonances in the inverted regime These modulations can be understood as a consequence of trapped excited-state populations that do not participate in the adiabatic transport and only contribute to the transport on resonance.
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