[Reporter Dabin Jeong of Veritas Alpha] Seoul National University's College of Engineering announced on the 18th that Professor Sunkyu Yoo and Professor Namkyu Park’s research team of the Department of Electrical and Computer Engineering (ECE) has implemented a three-dimensional topological pump that can modulate the frequency of light on a two-dimensional plane. The system utilizes the frequency space as a virtual synthetic dimension, allowing the implementation of complex three-dimensional phenomena on a two-dimensional plane. The research achievement was made through international collaboration with Professor Shanhui Fan of Stanford University in the United States and was published in the prestigious physics journal 'Physical Review Letters' on the 17th. Currently, semiconductor/optoelectronic manufacturing technology fundamentally relies on 2D structures and their stacking. In this case, there are limitations in exploiting the high degree of freedom in design that 3D structures such as cylinders and polyhedra can provide, making it challenging to control signals such as electricity or light as desired.

Recently in the scientific community, there has been active research on the concept of synthetic dimensions, which involves substituting spatial dimensions with other physical quantities to overcome such limitations. One approach is to redefine dimensions by associating spatial information with the unique frequency information that a component possesses. Through this technique, implementing physical phenomena of dimensions higher or equal to 3 become possible on a more easily manufacturable two-dimensional plane. Professor Sunkyu Yoo and Namkyoo Park's research team introduced the concept of synthetic dimensions and achieved the world's first implementation of Robert Laughlin's "topological pump" of a 3D cylindrical structure in a two-dimensional photonic circuit system. The implemented component utilizes the principles of topological physics, possessing robust characteristics against process errors during component fabrication. This is a significant advantage when dealing with optical components, where manufacturing processes are sensitive to errors down to the order of tens of nanometers (1 billionths of a meter).

The research team focused on the frequency axis of light, to extend the two-dimensional flow of light which is easily implementable in integrated circuits, to three dimensional domains. They achieved this by manipulating the medium through which light flows in space & time, demonstrating that light can flow as if on a three-dimensional cylinder. Furthermore, the space & time manipulation allowed the implementation of the topological characteristics of Laughlin's proposed pump by making light perceive a virtual magnetic field. Kim Ji-sung, the first author of the paper, stated, "While Laughlin pumps have been implemented in ultracold atomic systems before, there were no previous instances of implementations at room temperature with scalability. Additionally, by utilizing the frequency synthetic dimension, we succeeded in implementing high-dimensional topological phenomena that are difficult to observe in a lower-dimensional space."

The co-corresponding authors of the paper, Professors Sunkyu Yoo and Namkyoo Park, conveyed that based on this research, they can now control the color of light (i.e., frequency) very stably. They emphasized that this characteristic can be directly applied to devices such as topologically protected photon memory and photonic computing components. This research was led by undergraduate researchers Kim Ji-sung (first author; currently a Ph.D. candidate at the University of California, Berkeley) and Kim Kyung-hoon, while the project was conducted through the Basic Research Lab program funded by the Ministry of Science and ICT (BRL, Basic Research Lab for Electronics-Photonics Hybrid Memristic Devices), the Mid-Career Researcher program and the Young Researcher program at Seoul National University for Creative Leading in Science and Technology.

(From the left) Professor Sunkyu Yoo, Professor Namkyoo Park, Undergraduate Researcher Jiseong Kim(Currently a Ph.D. Candidate at UC Burkeley), Undergraduate Researcher Gyunghun Kim, Ph.D. Researcher Hyungchul Park / Picture from SNU

Source: https://www.veritas-a.com/news/articleView.html?idxno=491606

Translated by: Jiyong Yoo, English Editor of the Department of Electrical and Computer Engineering, cyoo7@snu.ac.kr