Physicists discover what controls the speed of quantum time

Physicists at the École Polytechnique Fédérale de Lausanne (EPFL) have developed a novel method to measure the duration of ultrafast quantum events without relying on external clocks. Their research reveals that quantum transitions, such as electrons shifting energy states after photon absorption, are not instantaneous but depend on the atomic structure of the material involved. This breakthrough addresses a longstanding challenge in quantum mechanics: accurately determining the timescale of quantum processes that occur within attoseconds (10⁻¹⁸ seconds). Traditional approaches to measuring such fleeting events have struggled because external timing devices can interfere with the quantum system, potentially altering the very phenomena under study. The EPFL team overcame this by exploiting the intrinsic properties of electrons emitted from materials when excited by light. Specifically, they analyzed changes in the electron’s spin—a quantum property that encodes information about the transition’s dynamics. By using spin- and angle-resolved photoemission spectroscopy (SARPES), the researchers could infer the duration of the quantum transition from the interference patterns created by multiple quantum pathways. This method eliminates the need for an external clock, relying instead on the electron’s wavefunction evolution from an initial to a final state. The findings demonstrate that the timing of quantum events is closely linked to the material’s atomic structure, offering new insights into the fundamental nature of time at the quantum level. This could have significant implications for the development of quantum technologies and deepen our understanding of quantum mechanics, where the concept of time remains a complex and debated topic. The research not only advances experimental techniques in ultrafast physics but also contributes to the theoretical framework by clarifying how time manifests in quantum transitions. As quantum systems become increasingly central to emerging technologies, such as quantum computing and ultrafast electronics, precise knowledge of quantum time scales will be crucial for optimizing performance and control.