2026/03/27(Fri) 10:30 -12:00 七樓研討室 7F, P7A Seminar Room
Title
Non-adiabaticity as a source of coherence and decoherence in quantum matter
Speaker
Dr. Matisse Wei-Yuan Tu (Max Planck Institute for structure and dynamics of matter)Abstract
Adiabatic dynamics provides a central reference framework across many branches of quantum science, underpinning both the geometric description of quantum evolution and the effective separation of electronic and nuclear motion in atomistic systems. The former is represented by the quantum adiabatic theorem, which forms the basis of physical realisations of Berry phase and curvature effects in quantum materials. For the latter, the Born–Oppenheimer approximation (also called adiabatic approximation) underlies first-principles electronic structure studies and practical molecular dynamics, and provides the conceptual basis for interpreting ultrafast lattice excitations, such as coherent phonons and related spectroscopies. These two adiabatic scenarios share the defining feature: the presence of slowly varying parameters. The essential difference lies in whether these parameters are externally controlled, such as the Bloch momentum in quantum materials, or they are themselves dynamical variables, namely, the nuclear degrees of freedom in atomistic considerations. This distinction naturally sets the stage for qualitatively distinct manifestations of non-adiabatic effects.
In this talk, I will present our results on two distinct manifestations of non-adiabatic effects, integrating insights from different theoretical approaches into a cohesive perspective.
The first work concerns laser-driven electronic systems in which band geometry plays an essential role in the resulting electronic response. Using a non-adiabatic wave-packet transport theory, we identify how non-adiabatic driving gives rise to band-geometric effects associated with interband coherence beyond those accessible in strictly adiabatic regimes. In particular, we find experimental support for the theoretically proposed distinction between spin-mediated contributions, relevant for spin-geometric effects, and non-spin-mediated components of the photocurrent [1].
The second work focuses on generic electron–nuclear correlated systems. Common belief holds that one must perform an ensemble average over the nuclear degrees of freedom in order to describe electronic decoherence. Using the exact factorisation method, we show that, contrary to this belief, non-adiabaticity can act as an intrinsic source of electronic decoherence even along a single classical nuclear trajectory [2].
Taken together, these results illustrate how non-adiabaticity provides a useful lens for advancing our understanding of coherence and decoherence dynamics in quantum matters.
[1] M. W.-Y. Tu, L.-S. Lin, C.-Y. Wang, J.-P. Chou, S.-Y. Wei, C.-M. Tu, C.-N. Kuo, C. S. Lue, and C.-W. Luo. Phys. Rev. B 112, 035417 (2025).
[2] M. W.-Y. Tu and E.K. U. Gross. Phys. Rev. Research 7, 043075 (2025).
Language
演講語言 (Language): in English