Présenté par Dr. Cesare TRONCI
University of Surrey, Royaume-Uni
Résumé : How does a classical particle interact with a quantum particle? After its appearance in measurement theory, quantum-classical coupling has represented a long-standing question in ab-initio methods for molecular dynamics. Conventional approaches beyond BornOppenheimer theory are often based on Born-Huang expansions invoking the existence of appropriate classical limits that are difficult to implement. On the other hand, mean-field methods generally possess a solid mathematical ground, but their applicability is very limited. Recently, we have proposed a new perspective in which challenging aspects related to classical limits are overcome by regarding part of a hybrid system as entirely classical from the start. This picture requires an unprecedented approach combining Koopman’s theory of classical wavefunctions with minimal coupling methods. Koopman wavefunctions on phasespace are little known in the community and Sudarshan’s first suggestion in 1976 of using them in quantum-classical coupling led to several issues. We solved these issues through a modification of Koopman’s original theory that retains information on the classical phase. Here, we will show how a new type of quantum-classical wave equation is capable of reproducing essential features in hybrid dynamics, thereby leading to a new quantum-classical density operator. Finally, we shall discuss the exact solutions for the spin-boson model in the pure dephasing approximation.
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