"There Is No Perfect Isolation"... DGIST Solves 10-Year Mystery of Quantum Collapse [Reading Science]

Cause of Electron Coherence Collapse in Open Quantum Systems Identified
Published in the International Journal Advanced Science

The fundamental cause of "decoherence," long considered a core challenge in quantum technology, has been identified for the first time by a team of Korean researchers. Decoherence refers to the phenomenon where the quantum property of maintaining multiple states simultaneously collapses due to interactions with the external environment. Experts say that this discovery could bridge the gap between conventional quantum theory—which assumes an ideally isolated state—and the realities of the physical world.

On March 25, the Daegu Gyeongbuk Institute of Science and Technology (DGIST) announced that a research team led by Professor Jae-dong Lee from the Department of Chemical Physics has, for the first time in the world, uncovered the microscopic mechanism by which quantum states collapse in an “open quantum system” in nature.

Light Emission Process: Broadband Emission and Superradiance. A Schematic of Broadband Emission. B Schematic of Superradiance. Provided by the Research Team

Quantum technologies assume a "perfectly isolated state" free from external interference, but in reality, all materials and devices constantly interact with their surroundings. During this process, the orderliness of quantum systems deteriorates. The precise cause of this phenomenon has remained an unsolved issue for more than a decade.

In particular, in the process known as high-harmonic generation, which occurs when intense light is shone on a solid, an "ultrafast decoherence" phenomenon is observed in which electron coherence collapses rapidly within just 1 to 2 femtoseconds. However, the reasons for such rapid decoherence have not been clearly explained until now.

Interaction with the Environment Determines Collapse

The research team solved the problem by newly implementing a computational method based on the "Lindblad master equation," which goes beyond the limitations of traditional quantum master equations. Through this, they established a precise theoretical model that simultaneously accounts for both electron-electron interactions and interactions between electrons and their surrounding environment.

The study found that, in solids, interference occurs between two phenomena—superradiance and broadband emission—that offset each other.

This interference effect shortens the scattering time of electrons and, as a result, is a key factor that drives quantum decoherence to occur rapidly, within just a few femtoseconds. In other words, the study revealed for the first time that the essence of quantum state collapse is not simply due to internal interactions, but is determined by "interactions with the environment."

From left, Jae-dong Lee, Professor of Chemistry and Physics at DGIST, Dr. Ki-min Bae. Provided by DGIST

This research is significant because it not only resolves the longstanding challenge of ultrafast electron decoherence in solids, but also provides the physical foundation necessary to expand quantum theory into practical technology.

Professor Jae-dong Lee of the Department of Chemical Physics at DGIST commented, "This study moves beyond the previous concept of isolated quantum systems, highlighting the need to design quantum technologies that account for real-world environments," adding, "It can be used in the development of next-generation quantum technologies, such as the search for new qubit candidates with long coherence times."

This research was supported by the Mid-Career Researcher Program of the National Research Foundation of Korea and DGIST's International Joint Research Program. The findings were published in the international journal Advanced Science.

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