Quantum mechanics and relativity are the two pillars of modern physics. However, for over a century, their treatment of space and time has remained fundamentally disconnected. Relativity unifies space and time into a single fabric called spacetime, describing it seamlessly. In contrast, traditional quantum theory employs different languages: quantum states (density matrix) for spatial systems and quantum channels for temporal evolution.

A recent breakthrough by Assistant Professor Seok Hyung Lie from the Department of Physics at UNIST offers a way to describe quantum correlations across both space and time within a single, unified framework. Assistant Professor Lie is first author, with Professor James Fullwood from Hainan University serving as the corresponding author. Their collaboration creates new tools that could significantly impact future studies in quantum science and beyond. The study has been published in Physical Review Letters.

In this study, the team developed a new theoretical approach that treats the entire timeline as one quantum state. This concept introduces what they call the multipartite quantum states over time. In essence, it allows us to describe quantum processes at different points in time as parts of a single, larger quantum state. This means that both spatially separated systems and systems separated in time can be analyzed using the same mathematical language.