2026-02-09 スイス連邦工科大学ローザンヌ校（EPFL）
＜関連情報＞
- https://actu.epfl.ch/news/measuring-time-at-the-quantum-level/
- https://www.cell.com/newton/fulltext/S2950-6360(25)00366-4
量子時間スケールの対称性への依存性 Dependence of quantum timescales on symmetry
Fei Guo ∙ Dmitry Usanov ∙ Eduardo B. Guedes ∙ … ∙ Arnaud Magrez ∙ Michele Puppin ∙ J. Hugo Dil
Newton Published:February 6, 2026
DOI:https://doi.org/10.1016/j.newton.2025.100374
Accessible overview
The concept of time has troubled philosophers and physicists for thousands of years, and the advent of quantum mechanics has not simplified the problem. The central problem, which can be broken down into several aspects, is the role of time in quantum mechanics. An important open question is the timescale associated with a quantum transition. Energy conservation dictates that such transitions cannot be instantaneous, and their timescale is expected to be in the attosecond (10−18 s) range. The challenges of experimentally accessing such timescales lie not only in the fact that they are extremely short but also that using an external timescale risks inducing artifacts. Both challenges can be resolved using quantum interference methods, based on the connection between accumulated phase and time. Here we use the spin of electrons emitted in the photoemission process as an observable of this phase and thus of the timescale of the process itself. These experiments do not require an external reference or clock and yield the timescale required for the wave function to evolve from an initial to a final state at a higher energy upon photon absorption. This time interval is measured for materials with different dimensionality and correlation strength, and a direct link between this dimensionality, or rather symmetry, and the transition timescale is found. Besides yielding fundamental information for understanding what determines the time delay in photoemission, our experimental results provide further insight into what factors influence time on the quantum level and to what extent quantum transitions can be considered instantaneous; they serve as an important piece in the puzzle of time in quantum mechanics.
Highlights
- The absolute quantum transition timescale is accessed via the photoelectron spin
- An absolute time duration is experimentally estimated without any time reference
- The attosecond transition timescale increases with reduced dimensionality
- This method yields an alternative to characterize interaction strength in materials
Summary
The role of time in quantum mechanics and the timescale associated with quantum transitions remains an open question in physics, especially on an experimental level. Here we use an experimental method based on spin- and angle-resolved photoemission spectroscopy from spin-degenerate dispersive states to determine the Eisenbud-Wigner-Smith time delay of photoemission. This timescale of the quantum transition is measured for materials with different dimensionality and correlation strength. A direct link is found between the dimensionality, or rather the symmetry, of the system and the attosecond timescale of the quantum transition. The quasi 2-dimensional transition metal dichalcogenides 1T-TiSe2 and 1T-TiTe2 show timescales around 150 as, whereas in quasi 1-dimensional CuTe, the transition takes more than 200 as. This is in stark contrast with the 26 as obtained for 3-dimensional pure Cu. These results provide new insights into the role of symmetry in quantum timescales and may provide a route to understanding the role of time in quantum mechanics.
