A new study published in Physical Review Research by the University of Eastern Finland (UEF) investigates the behavior of photons, the fundamental particles of light, as they approach boundaries where material properties change rapidly over time. This study discovers amazing quantum optical phenomena that may improve quantum technology and pave the way for a promising new field: four-dimensional quantum optics.
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Four-dimensional optics is a scientific field that studies light scattering from structures that alter in time and space. It has enormous potential for developing microwave and optical technology by enabling features like frequency conversion, amplification, polarization engineering, and asymmetric scattering. This has piqued the interest of numerous researchers worldwide.
Previous years saw substantial progress in this area. For example, this recent international study, which also involved UEF, demonstrates how integrating optical properties such as resonances can significantly alter the interaction of electromagnetic fields with time-varying two-dimensional structures, opening up new options for controlling light.
Building on their previous study in classical optics, UEF researchers have now expanded their examination into quantum optics. The researchers thoroughly analyzed quantum light interaction with a material whose macroscopic properties change suddenly across time, resulting in a single temporal interface between two separate media.
Four-dimensional quantum optics is the next logical step, allowing us to explore the implications of this area for quantum technology. Our research has taken this initial step and now provides a foundational tool for us to examine complex structures, changing in time and space, for uncovering novel quantum optical effects.
Dr Mohammad Mirmoosa, Study Lead Researcher and Project Researcher, University of Eastern Finland
The investigation found and demonstrated various exciting phenomena, including photon-pair creation and annihilation, vacuum state generation, and quantum state freezing, all of which could have uses in quantum technology.
The researchers realize that this is only the beginning. Four-dimensional quantum optics is emerging as an area that will receive much attention in the next years. For example, studying how quantum light fields interact with regularly repeating time interfaces, known as photonic time crystals, is particularly intriguing.
Dr Mirmoosa added, “In our paper, we did not take into account dispersion. Real materials are nonetheless dispersive in nature, meaning that responses have a delay relative to the excitations. To address such an intrinsic feature necessitates the development of a more comprehensive theory.”
“Incorporating dispersion may lead to new possibilities for controlling the quantum states of light, and I am very motivated to explore that,” Dr Mirmoosa concluded.
Journal Reference:
Mirmoosa, M. S. et. al. (2025) Quantum state engineering and photon statistics at electromagnetic time interfaces. Physical Review Research. doi.org/10.1103/PhysRevResearch.7.013120