A recent study from the University of Eastern Finland (UEF) examines how photons—the fundamental particles of light—behave when they encounter sudden changes in a material’s properties over time. This research reveals intriguing quantum optical effects that could advance quantum technology and help establish an emerging field known as four-dimensional quantum optics.

Four-dimensional optics is a field of research that explores how light interacts with structures that change both in time and space. This emerging area has the potential to revolutionize microwave and optical technologies by enabling capabilities such as frequency conversion, amplification, polarization control, and asymmetric scattering. Because of these possibilities, it has drawn significant interest from researchers worldwide.

In recent years, substantial progress has been made in this field. For example, a recent international study published in Nature Photonics, which included researchers from the University of Eastern Finland (UEF), demonstrated how adding optical features like resonances can dramatically affect the interaction of electromagnetic fields with time-varying two-dimensional structures. This breakthrough opens new possibilities for controlling light in novel ways.

Extending Research into the Quantum Realm

Building on their previous work in classical optics, UEF researchers have now expanded their focus to quantum optics. Their latest study examines how quantum light interacts with a material that undergoes a sudden change in its macroscopic properties, creating a single temporal interface between two different media. This is similar to the boundary between air and water, but instead of occurring in space, it happens in time.

Dr. Mirmoosa, the lead researcher in this study, explains: “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.”

Unveiling Strange and Exciting Quantum Phenomena

The investigation showed and revealed several intriguing phenomena, including photon-pair creation and annihilation, vacuum state generation and quantum state freezing, all of which may have potential applications in quantum technology.

The researchers acknowledge that this is just the beginning. Four-dimensional quantum optics becomes an emerging field poised to attract significant attention in the near future. For instance, exploring how quantum light fields interact with periodically repeating time interfaces, known as photonic time crystals, is particularly exciting.

Future Challenges and Expanding the Theory

Dr. Mirmoosa adds: “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.”
He continues: “Incorporating dispersion may lead to new possibilities for controlling the quantum states of light, and I am very motivated to explore that.”

The study was published recently in Physical Review Research.

Reference: “Quantum state engineering and photon statistics at electromagnetic time interfaces” by M. S. Mirmoosa, T. Setälä and A. Norrman, 31 January 2025, Physical Review Research.
DOI: 10.1103/PhysRevResearch.7.013120