2024-09-20 06:40:17
In quantum mechanics, particles can exist in multiple states at the same time, defying the logic of our everyday lives. This property, known as quantum superposition, is the basis of new quantum technologies that promise to transform computing, telecommunications and sensing systems.
But quantum superpositions face a major challenge: quantum decoherence. During this process, the delicate superposition of quantum states breaks down as it interacts with its surrounding environment.
Harnessing the power of chemistry to build complex molecular architectures for practical quantum applications requires understanding and controlling quantum decoherence so that molecules with specific quantum coherence properties can be designed. This requires knowing how to modify the chemical structure of a molecule to modulate or mitigate quantum decoherence. This requires knowing the “spectral density,” a value that indicates how fast the environment is moving and how strongly it interacts with the quantum system.
Traditionally, quantifying this spectral density in a way that accurately reflects the intricacies of molecules has been beyond the reach of theory and experiment. However, now a team comprising, among others, Ignacio Gustin and Ignacio Franco, both from the University of Rochester in the United States, has developed a method to determine the spectral density in the case of molecules located in a solvent.
Thanks to the determined spectral density, it is not only possible to determine how fast decoherence occurs, but also to know which part of the chemical environment is primarily responsible for it. Scientists can thus trace decoherence pathways to connect molecular structure to quantum decoherence in the least problematic way possible.
The team used their method to show, for the first time, how electron superpositions in thymine, one of the building blocks of DNA, unravel in just 30 femtoseconds after absorbing ultraviolet light. A femtosecond is one-millionth of a billionth of a second.
They found that a few vibrations of the molecule dominate the initial steps of the decoherence process, while the solvent dominates the later stages. Furthermore, they discovered that chemical modifications of thymine can significantly alter the rate of decoherence, with hydrogen bonding interactions near the thymine ring leading to faster decoherence.
The study is titled “Mapping electronic decoherence pathways in molecules” and has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS).