Creating photonic time crystals presents major opportunities but also significant challenges. The biggest challenge is the need for substantial changes in material properties to make a noticeable momentum bandgap. Achieving this in optics is very difficult with current and possibly future materials because their ability to change properties is generally small.
A new study from the University of Eastern Finland investigates how photons, the particles of light, behave when they encounter rapidly changing material boundaries. This research reveals amazing quantum optical phenomena that could advance quantum technology and lead to a new field: four-dimensional quantum optics.
Four-dimensional optics studies how light interacts with structures that change in time and space. This field can improve microwave and optical technologies by enabling functions like frequency conversion and amplification, which is why many researchers are interested in it.
Researchers showed how adding optical features like resonances can significantly affect the interaction of electromagnetic fields with time-varying two-dimensional structures, opening new ways to control light.
Based on their past work in classical optics, UEF researchers have explored quantum optics. They studied how quantum light interacts with a material whose properties suddenly change over time, creating a single time-based interface between two media (like an air-water boundary but in time).
Dr. Mirmoosa, the lead researcher, said that four-dimensional quantum optics allows them to explore its effects on quantum technology. Their study revealed interesting phenomena like photon-pair creation, vacuum state generation, and quantum state freezing, which could be helpful to for quantum technology.
The researchers see this as just the beginning. Four-dimensional quantum optics is emerging and will likely attract more attention. For example, studying how quantum light interacts with repeating time interfaces, called photonic time crystals, is exciting.
Dr. Mirmoosa noted that their paper didn’t consider dispersion. Real materials have delays in their responses, which requires a more complete theory. He believes that addressing dispersion could lead to new ways to control quantum light states and is eager to explore it.
Journal Reference:
- Wang, X., Garg, P., Mirmoosa, M.S. et al. Expanding momentum bandgaps in photonic time crystals through resonances. Nat. Photon. 19, 149–155 (2025). DOI: 10.1038/s41566-024-01563-3
